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TBM and Lining - Essential Interfaces

Nguyen Duc Toan

Prof. Daniele Peila

Dr. Harald Wagner



TBM and Lining

Essential Interfaces

Student:

Nguyen Duc Toan

Dissertation submitted to the

Politecnico di Torino,Consortium for the Research and Permanent Education (COREP), and

D2 Consult Dr. Wagner Dr. Schulter GmbH & Co. KG

in partial fulfillment of the requirements

for the degree of

Master

in

Tunnelling and Tunnel Boring Machines

Academic Tutor:

Prof. Daniele Peila

Company Tutor:

Dr. Harald Wagner

Turin, Italy

October 2006



Abstract

Optimization of segmental lining design and construction, in close relation with proper

selection and operation of the tunnel boring machine (TBM), are the two among major

concerns for the owners, designers and contractors, in all tunnelling areas. The main

task of this work is to deal with this subject, using both qualitative and quantitative

approaches.

It is challenging to achieve the attractive and effective mechanized tunnelling

alternatives in saving both time and cost without a comprehensive and interdisciplinaryconsideration. The Parties involved should be aware of the proper approaches in

adopting the mechanized tunnelling technology for a given tunnel project. Every TBM

tunnel project needs to be feasible from both operational and engineering points of view, environmentally acceptable and value for money.

A significant scrutiny on the critical cases of TBM excavation has been conducted to

identify and rectify the obscure aspects that are often associated with TBM tunnelling,

in terms of risk management and project management. Difficult or critical cases of

excavation in various mechanized tunnelling techniques (with certain kinds of TBMs)

are analysed in connection with face stability and ground reinforcement issues.

The report identifies and describes both the technical aspects and the economic impact

of the critical interaction between the TBM and the tunnel lining. The interaction

between the soil and the TBM tunnelling process and a number of essential loadingcases for the segmental concrete lining has been investigated to comprehend the lining

behaviour, the risk of ground failure and the risk of surface subsidence. The parametricstudy was restrictively applied to the hydroshield tunnelling technique.



Acknowledgement

I would like to express my sincere appreciation to the following people who have helped

make this master thesis materialized:

Politecnico di Torino:

I would like to sincerely thank my academic tutor, Prof. Daniele Peila for his nicely

arranging a good placement for my internship, for his kindly keeping track of my Stage

work in Linz, and for his support in writing of this thesis. Prof. Sebastiano Pelizza is

always an inspiration to my striving and achievements. The two of them, as being the

Director and Assistant Director of the master program, make the most contribution to its

successfully realization and accomplishment.

I would like to express my thankfulness to Prof. Pier Paolo Oreste and Prof. ClaudioOggeri for the technical materials, for their help in exploring the university library and

their input in modelling. I would like to thank Prof. Marilena Cardu for the books on the

blasting technology. I would also like to thank other professors of Politecnico di Torino

for their useful lectures.

International Tunnelling Association (ITA) and Sponsor Companies/Societies:

I would like to gratefully acknowledge the ITA for its initiative and endeavour to activate

and sponsor this unique study course. The lectures at the master course in Turin are a good

source of reference for my work. I would like to convey my deep gratefulness to all mylecturers from a good deal of companies/societies/universities (as shown on the back cover

of this report) and from different nationalities who have dedicated their time and efforts to

come to Turin and teach us international students very high-quality lessons.

Consortium for the Research and Permanent Education (Corep):

Special thanks are due to Ms. Irene Miletto and Ms. Giusy Favasuli the Corep’s

Organizational Coordinators of the Master course in Turin.

My sincere thanks are delivered to Mrs. Luisa Rosano the COREP Secretariat who always

ensures the insurance coverage for my movement within and outside Italy, as well a goodadministration in general.

Master class:

I would like to thank all colleagues in the master tunnelling course in Turin, academic year

2005-2006, for maintaining a comfortable and pleasant atmosphere, and for their support

in my studying in terms of discussions and material exchange, particularly, Mr. Daniele

De Lazzari, Mr. Nick Chittenden, Mr. Kim Jin Ha, Mr. Bang Gyu Min, Mr. Nicola

Donadoni, Mr. Marco Della Casa, Mr. Ciprian Eduard Partenie, Miss Katia Efpraxia

Demirtzoglou, and Miss Lamprini Goli.



D2-Consult Team in Linz:

I would like to thank Ms. Katrin Pesendorfer, Ms. Margarete Prendl and Ms. Michaela

Zellner the D2-Consult secretariat, for their valuable assistance during the whole process

of my internship in Linz, Austria from beginning of May to mid-July 2006.

I would like to thank Mr. Ulrich Horny for allowing citations from his technical paper, andfor his wholehearted and effective guidance on numerical modelling during my Stage.

Thanks are due to Mr. Walter Pointner, without his explanation I could be hardly to

interpret the technical drawings of the BEG railway tunnel project which are presented

only in German language. I also highly appreciate his high sense of humour, which makes

my stay in the Danube city worth remembering.

Mr. Peter Ertl and Mr. Horst Wöger, who helped me to find and explore the necessary

contract documents and drawings, deal with computer problems and everyday life

difficulties. Accompanying them to the BEG Project in Innsbruck - Southern Austria is a

good memory of mine.

Finally, heartfelt gratitude is conveyed to Mr. Andreas Beil, Dr. Harald Wagner and Dr.Alfred Schulter, Managing Directors of D2 Consult for their availability to any help I

need. Their partly but valuably covering for the living cost is indispensable to my Stage

period. A special point I would like to be grateful to them is that, they kindly allowed me

to freely utilize all the company resources, such as a rich library, photocopy machine,

scanner, printer, and limitless access to the Internet. The technical documents I collected in

Linz are much helpful to my thesis finalization in Turin and will be greatly beneficial to

my future career. The constant input through consultation with Dr. Wagner together with

his writings is a never-ending source for my work. And I am very proud of being a "close

friend of D2 Consult team" as allowed by Dr. Wagner and inspired from Mr. Martin Srb.

Thanks are also due to the Brenner Eisenbahn GmbH (BEG) for the kind permission to use

the company's respective information. Prof. Gunter Swoboda of the Innsbruck University

(Austria) is appreciated for the nice talking at his Laboratory and for his helpful input on

the analysis of the settlement induced by tunnelling, as well as other modelling aspects.

Institute of Transport Science and Technology (ITST):

My leaders in the Institute of Transport Science and Technology in Hanoi deserve my

sincere thanks for their support in the first steps of enrolling in this master course. I am

also thankful to my colleagues in the ITST’s Underground Structures Department for their

consistently being kind and willing to help me.

My family:

I am deeply grateful to my parents, who have provided most of finance for my stay in

Europe. I am greatly indebted to my wife Tran Thi Linh Chi for her support,

understanding and patience. Much love and thank is due to my son Nguyen Ung Bach for

his constantly missing me and passionately wanting me being back home. I would like to

dedicate this thesis to my parents, my wife and my son.



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Contents

Abstract

Acknowledgement

Table of Contents

1. INTRODUCTION .................................................................... ............................................................. 1

1.1 BACKGROUND................................................................................................................................1 1.2 OBJECTIVES...................................................................................................................................3 1.3 CONTENTS OF THE THESIS ............................................................................................................4

2. CONSTRAINTS OF A NEW RAILWAY LINE....................................................................... .........6

2.1 BEG COMPANY APPROACHING THE PROJECT ............................................................................6 2.2 THE PROJECT ALIGNMENT ...........................................................................................................6 2.3 TBM CONTRACT LOT H3-4 AND H-8 ...........................................................................................9

3. ESSENTIAL INTERFACES OF EXCAVATION............................................................................12

3.1 OVERVIEW ON DIFFERENT TUNNELLING METHODS .................................................................12 3.1.1. General ...................................................................................................................................12 3.1.2. Classif ication of Mechanized Tunnell ing Techniques ..........................................................13

3.2 GLOBAL VIEW OF TBM TUNNELLING .......................................................................................15 3.2.1 TBM Types ..............................................................................................................................15 3.2.2 Operation of TBMs .................................................................................................................21 3.2.3 Conventional Tunnell ing Versus TBM Tunnelli ng ..............................................................28

3.3 CRITICAL CASES OF TBM EXCAVATION ...................................................................................32

3.3.1. Risk Management for Tunnels ...............................................................................................32 3.3.2. Criti cal Cases of TBM Tunnelli ng in Soil .............................................................................37 3.3.3. Criti cal Cases of TBM Tunnelli ng in Rock ...........................................................................41 3.3.4. TBM Tunnelli ng in M ixed Face Conditions .........................................................................51

3.4 GROUND R EINFORCING ..............................................................................................................52 3.4.1. General ...................................................................................................................................52

3.4.1.1 Face Support ...............................................................................................................................52 3.4.1.2 Failure Mechanism .....................................................................................................................52 3.4.1.3 Countermeasures to Ground Failure ........................................................................................60 3.4.1.4 Grouted Bodies ...........................................................................................................................61

3.4.2. Case History: Metro of Turi n .................................................................................................65 3.4.2.1 Subsoil Conditions ......................................................................................................................66 3.4.2.2 Shield Machines ..........................................................................................................................67 3.4.2.3 Tunnel Lining and Excavation ..................................................................................................69 3.4.2.4 Ground Improvement.................................................................................................................70

4. INTERFACE BETWEEN TBM AND LINING ................................................................... ............75

4.1 TYPES OF LININGS .......................................................................................................................75 4.1.1 General ...................................................................................................................................75 4.1.2 Rein for ced Concrete L in ings .................................................................................................80 4.1.3 Steel F iber Rein forced Linings ..............................................................................................82

4.2 LINING DESIGN PROCEDURE ......................................................................................................82 4.2.1 Design Steps ............................................................................................................................83 4.2.2 Loading Conditions ................................................................................................................85

4.2.2.1 Geostatical Loads........................................................................................................................88 4.2.2.2 Thrust Jacking Loading .............................................................................................................89 4.2.2.3 Trailer Loading...........................................................................................................................90 4.2.2.4 Grouting Loads ...........................................................................................................................91 4.2.2.5 Storage Loads..............................................................................................................................92 4.2.2.6 Erection Loads ............................................................................................................................93



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4.2.2.7 Fire Loads....................................................................................................................................93 4.2.2.8 Other Loads ................................................................................................................................93

4.3 CONCEPT OF INTERFACE ............................................................................................................94 4.3.1 Contractual I nterf ace .............................................................................................................95

4.3.1.1 General Aspects ..........................................................................................................................95 4.3.1.2 Segmental Lining Optimization.................................................................................................97

4.3.2 Physical Interface .................................................................................................................101 4.3.2.1 General ......................................................................................................................................101 4.3.2.2 Machine Operation ...................................................................................................................103 4.3.2.3 Guidance System.......................................................................................................................105 4.3.2.4 Lining Ring Building ................................................................................................................106 4.3.2.5 Backfill Grouting ......................................................................................................................113 4.3.2.6 Back-up System.........................................................................................................................115 4.3.2.7 Monitoring and Instrumentation.............................................................................................116

5. INFORMATION FOR SETTLEMENT STUDY ...................................................... .....................118

5.1 GROUND CONDITIONS ...............................................................................................................118 5.2 EXCAVATION AND SUPPORT......................................................................................................120

5.2.1 Shield Machine .....................................................................................................................120 5.2.2 Ring Configuration ..............................................................................................................121

5.2.3 Li ning Material .....................................................................................................................123 5.3 NUMERICAL ANALYSIS TOOL ...................................................................................................124 5.3.1 Soil Models in Plaxis ............................................................................................................124 5.3.2 Hardening Soil M odel ..........................................................................................................125

5.4 FLOWCHART OF CALCULATION ...............................................................................................127

6. TUNNEL INDUCED GROUND DEFORMATION.......................................................................129

6.1 SETTLEMENT INDUCED BY TUNNELLING .................................................................................129 6.1.1 Volume Loss and Settlement ................................................................................................129 6.1.2 Settlement Calcul ation Approaches .....................................................................................132 6.1.3 Settlement Contr ol Approach ...............................................................................................134

6.2 EMPIRICAL CALCULATION FOR SETTLEMENT.........................................................................135 6.2.1 Formulae ..............................................................................................................................135

6.2.2 Calculated Resul ts ................................................................................................................144 6.3 FINITE ELEMENT MODELLING .................................................................................................149 6.3.1 Introduction ..........................................................................................................................149 6.3.2 FE Analysis by Plaxi s 2D Pr ofessional ...............................................................................150

6.3.2.1 Geometry ...................................................................................................................................151 6.3.2.2 Calculations ...............................................................................................................................153

6.3.3 Face Stabili ty by Plaxis 3D Tunnel .....................................................................................160 6.3.3.1 Geometry ...................................................................................................................................161 6.3.3.2 Calculations ...............................................................................................................................164

6.4 SUMMARY ..................................................................................................................................171

7. CONCLUSIONS AND FUTURE WORK.......................................................................................173

List of Acronyms

References

Appendixes

Curriculum Vitae



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Chapter 1

1. Introduction

1.1 Background

Placement of the Internship

The Master course in Tunnelling and Tunnel Boring Machines Edition V 2005/2006 isheld by the Turin University of Technology (Politecnico di Torino) in partnership withthe Consortium for the Research and Permanent Education (Corep) in Turin, Italy. Theintense study period has brought rich and fruitful knowledge to all the internationalstudents, including the author.

After that, the author has had a fruitful master trainee period (or internship/stage) in theHeadquarter of the D2 Consult Dr. Wagner Dr. Schulter GmbH & Co. KG, located inLinz, Austria. The internship lasted more than two months. The author's host company

tutor is Dr. Harald Wagner - Managing Director of the D2 Consult GmbH, and hisacademic tutor is Prof. Daniele Peila of the Politecnico di Torino.

The host company profile

D2 Consult Dr. Wagner Dr. Schulter GmbH & Co. KG

Hirschgasse 32

4020 Linz, Austria

Managing Directors: Harald Wagner, Ph.D., P.E.Alfred Schulter, Ph.D., P.E.

Established: 1985

Natural Duality is the founding concept of D2 Consult. D2 Consult Linz is the Headoffice of D2 Consult. Most projects have been being handled in Linz.

Branch Offices: 1986 - Foundation of Branch Office "USA"

1996 - Foundation "D2 Consult Colombia"

1998 - Foundation "D2 Consult Prague"



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2000 - Foundation "D2 Consult Berlin

Activities:

• Design and analysis of underground structures

• Tender documentation

• Technical assistance

• Construction supervision

• Project management

• Cost estimation

In the fields of Transportation, Energy, and Environment, with reference projects in allover the world.

In connection with the purpose of the internship, two projects using tunnel boringmachines (TBM) and reinforced concrete segments completed in Paris and Boston areintroduced in the Appendix 1 and 2, respectively.

Jobsites

From Linz the author also went to visit the BEG (Brenner Eisenbahn GmbH) RailwayProject in Innsbruck, southern Austria. While gaining knowledge of the BEG project,under the guidance of the persons responsible for the checking of the project design,

i.e. D2 Consult Linz Team, the author could have a thorough grasp of the upgradingwork of the railway line on the Brenner Railway Axis. The upgrading focuses on theconstruction of the new high capacity line in the Lower Inn Valley in the Tyrol

province of Austria. The author has also found background information about the project’s history and milestones as well as the data on the BEG company.

- Project Name: BEG (Brenner Eisenbahn GmbH) Railway Project

- Location: Lower Inn Valley, Tyrol province, Austria (between Kufstein andInnsbruck)

- TBM (Tunnel Boring Machine) Tunnel Sections:

i) Contract Lot H3-4 from Münster at Km 33.1 to Wiesing at Km 38.9, length L =5.818 km.

ii) Contract Lot H8 in Jenbach from Km 39.6 to Km 44.8, length L = 5.19 km.

Two these TBM Lots are both at the beginning stages of construction.

Purposes of the Internship

During the trainee period the author continued to gain greater knowledge of tunnellingtechnology. This enabled for a better preparation of the present thesis.



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The sector of reference for the traineeship is the tunnel design, on the general subjectDesign and/or construction aspects of tunnel and underground works. The contentsinclude looking over the parameters of tunnel construction; studying critical cases of TBM excavation; and studying interface between TBM and segmental concrete lining.

The overall objectives are enrichment of professional experience; check and wideningof the knowledge acquired during the lectures. The specific objective is project reviewand evaluation.

The tasks are: Assistance in review and independent checking of structural tunneldesign, including calculations of lining segments, temporary and permanent loadings,in coordination with actual construction and monitoring.

Investigation of technical aspects

The following tasks which partly comprise the content of the present report have beenaccomplished during the internship period in D2 Consult Linz:

• Study of the BEG project’s contract documents and drawings, with techniquesin the field of conventional and mechanized tunnelling. This is a challengingtask because all the Contract Documents are in German, and only a few onesare in English. This difficulty is partly released by the fact that, D2 Team,especially Mr. A. Beil, has allowed me to make quotations from the company'savailable English sources.

• Investigation of critical cases of TBM excavation and study on interface between TBM and tunnel lining, including:

Review of details of structural lining aspects, during construction phaseand in the service condition

Review of ground movements and volume loss due to an advancingtunnel heading

Performing some parametric studies on the tunnel lining calculation

After two months and a half from the beginning of May to mid-July 2006, an

Internship report has been submitted to the Corep, Politecnico di Torino, and D2Consult the host company. After that, the Internship report has been further developedinto a full thesis as in the present form.

1.2 Objectives

This study is initiated in order to increase TBM applicability in both urban andsuburban areas, as well as in other fields of underground works, by reviewingimportant engineering aspects of TBM tunnelling.



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The report describes the critical cases of TBM excavation in general, and essentialloading cases for the segmental concrete lining in particular. Both the technical aspectsand the economic impact of the critical interaction/interface between the TBM and thetunnel lining will be analysed. From that interfaces, necessary lessons and/or reactionswill be illustrated and envisaged, both from theoretical and practical point of view.

This report is intended to integrate as many as possible the parameters/interdependentfactors that come into play during lining design and subsequent construction of aquality structure.

In order to illustrate part of that interfaces in the form of visible digits, numericalanalyses for the problems of tunnel face stability and surface subsidence are carriedout.

1.3 Contents of the Thesis

The thesis contains seven chapters followed by references, as described below:

• Chapter 2 introduces general information about the BEG company and the wayapproaching the Brenner axis upgrade project within Austria territory. TheHigh-speed Railway Brenner in Austria is part of the European north-southrailway axis, and the TBM Contract Lot H3-4 within the project is the subjectof this study, among others.

• Chapter 3 describes the essential interfaces of TBM excavation, by first briefing on different tunnelling methods, then going more detailed into TBMtunnelling method, and addressing critical cases of TBM excavation. In briefingdifferent tunnelling methods, classifications of mechanized tunnellingtechniques are given. In running through the TBM tunnelling, available types of TBMs and their basic operation are discussed, together with a short comparison

between conventional and TBM tunnelling. Finally, critical cases of TBM

excavation are dealt with in several subtopics such as project management, risk management, and difficulties while driving tunnels in soil, rock and mixedground. A separate part is reserved for dealing with the face stability andground reinforcing problems in urban tunnelling, and presenting a case historyof Turin Metro Line 1.

• Chapter 4 presents the interface between TBM and lining. Looking at certaintypes of tunnel lining will lead to the concept of contractual and structuralinterface. The investigation on these two interlinked interfaces also leads to a

discussion on the possibility of segmental lining optimization. Next, critical



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loading cases, among others, for the lining of tunnels driven by TBMs, aregiven.

• Chapter 5 contains the input data for parametric studies that will be performed

in the Chapter 6. These include a flowchart of calculation, very shortintroduction to the numerical tool, ground conditions, lining configuration, andthe loads to be considered.

• Chapter 6 contains computations of the ground volume loss and surfacesettlements induced by tunnelling. Both empirical approach and numericalmodelling are carried out to compare one another and extract necessaryconclusions. The numerical modelling can also gives member forces in thetunnel lining.

• Chapter 7 contains several conclusions obtained from the thesis. Theseconclusions have shown that the presented extensive analyses on projectinterfaces sufficiently address the TBM processes with many influential factors.These analyses are necessary to allow for economic and reliable technicalsolutions and other requirements from the Client, within the scope of themechanized tunnelling techniques. This chapter also contains recommendationsfor the author's future studies.

• List of Acronyms

• References



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Chapter 2

2. Constraints of a New Railway Line

2.1 BEG Company Approaching the Project

The Brenner Eisenbahn GmbH (BEG) was founded as an infrastructure constructioncompany owned by the Republic of Austria and since 2005 it is a subsidiary of theÖBB Infrastruktur Bau AG, which is a company of the ÖBB group (Austrian FederalRailway). Since 1996 the BEG has been working on the implementation on Austrianterritory of the European railway upgrade project for the Brenner axis. In the past yearsthe BEG has organized the finance, completed the environmental impact assessmentsand obtained the necessary approvals for the first section of the project in the Lower Inn Valley. Construction work for the new line began in the summer 2003. Thecompany’s headquarters are in Innsbruck, Austria.

For the southern leg of the new rail link, the BEG has been collaborating with the

Italian National Railway (RFI) on the Brenner Base Tunnel project. Since 2005 theBrenner Base Tunnel SE has taken on the planning of the Tunnel.

The BEG's consent for visiting the construction site, the BEG staff's considerate guideduring the site visit, and its permission for use of the project information, are highlyappreciated.

2.2 The Project Alignment

History

In December 1994, the European Council pinpoints 14 priority infrastructure projectsfor the development of a common transeuropean transport network (TEN-projects).The upgrading of the railway line Berlin - Nuremberg - Munich - Kufstein - Innsbruck - Brenner - Verona is classified project number 1.

In August and October 2003, the construction of the main lot between Vomp andTerfens (near Innsbruck) was started.



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Finance

The rail upgrade program in the Lower Inn Valley between Kufstein and Innsbruck is aEuropean project. As part of the Berlin - Palermo TEN axis, it occupies a key positionfor future developments in international north - south traffic management. On the basis

of the decisions taken to develop the Trans-European Transport Networks (TEN), theEuropean Union (EU) is co-financing the Lower Inn Valley railway project, with 50 percent of planning costs and 10 percent of construction costs funded via the relevantEU budgets.

At 2003 price levels, the first upgrade section of the Lower Inn Valley railway isexpected to cost about 1.85 billion euros. In addition to EU funding, the necessaryfinance will be provided by the Austrian government.

Implementation

For the Brenner axis upgrade, the European Union’s transport-policy makers havedecided on a step by step approach. First priority has been given to the section betweenKundl and Baumkirchen in the Lower Inn Valley, a two-track line which currentlyhandles more than 300 trains a day and where a sustainable increase in the volume of traffic is not an operative possibility with the existing infrastructure. To that extent theLower Inn Valley can be described as the bottleneck of international north-south railtraffic over the Brenner and has to be upgraded to increase capacity. The new Kundl-Baumkirchen section is already under construction, and the second upgrade sectionfrom Kundl to Kiefersfelden is now in the planning stage.

The BEG began main construction work on the new Lower Inn Valley railway inAugust 2003 with the award of the first main construction lot. Meanwhile six of tenmain construction lots are under construction (Lot H2-1, H3-4, H4-3, H5, H6, H7); theones to be awarded are on schedule (H2-2, H3-6, H8, H1). The tunnelling techniques used vary from conventional drill and blast to hydro shield machines for the crossingof the valley or special techniques like open cut with underwater concrete invert or tunnel excavation with jet grouting.

Contract lots and state of construction works are shown in Figure 1.



Figure 1: Brenner axis upgrade project, its contract lots and state of construction work



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2.3 TBM Contract Lot H3-4 and H-8

Owner BEG Brenner Eisenbahn GmbH

BEG Project as a

Whole

The High-speed Railway Brenner in Austria is part of theEuropean north-south railway axis. This section has a totallength of 39 km and runs predominantly in the underground or in trough structures.

The total length of the double track tunnels is about 28 km.

3 additional investigation tunnels have a total length of 9.8km. During operation, they will be used as evacuation tunnels.

The design in the 3 stages - preliminary, tender, and finaldesign - comprises conventional methods within the principlesof NATM, the methods TBM, Jet grouting, and cut and cover method under air pressure.

Details of Lot H3-4

Münster - Wiesing

Lot H3-4 Münster - Wiesing has a total length of 5.8 km, witha minimum overburden of approx. 8.5 m. The TBM tunnel(Hydro-Shield-TBM) has an excavation diameter of approx.12.90 m. The lining consists of concrete segments with 0.5 m

thickness and fire protection inner lining with 0.2 m thickness.The tunnel crosses the river Inn with low overburden, as wellas the motorway A12 and the existing tracks of the AustrianRailway.

Services Provided

by D2 Consult• Review of preliminary-, tender- and final design

• Review of statical calculation

• Structural analysis for the fire loading case

• Consultancy services during construction

Period of Work 01/2000 – 06/2009

Details of Lot H8

Jenbach/Stans

Lot H8 Jenbach - Stans has a total length of 5.19 km (3.5 kmwith Hydro-Shield-TBM), with a minimum overburden of approx. 6.0 m. The TBM tunnel has an excavation diameter of approx. 12.90 m. The lining consists of concrete segmentswith 0.5 m thickness and fire protection inner lining with 0.2m thickness.

The tunnel crosses the motorway A12 and the existing tracks



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of the Austrian Railway with low overburden.

Services Provided

by D2 Consult• Review of preliminary-, tender- and final design

• Review of structural calculation

• Technical assistance

• Structural analysis for fire loading cases

• Consultancy services during construction

Period of work 03/2000 – 12/2008

Some preliminary information on the tunnel cross sections, anticipated TBMs and

lining segments are shown in Figure 2 to Figure 4. TBM for Lot H3-4 will be deliveredto the site in beginning 2007, and TBM for Lot H8 to be delivered in autumn 2007.

Figure 2: Cross section with escape tunnel and escape shaft. Lot H8 Jenbach



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Figure 3: Normal cross-section, two tracks upgrading with fire prevention lining. LotH8 Jenbach

Figure 4: Anticipated TBM and segments (BEG, 2005)



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Chapter 3

3. Essential Interfaces of Excavation

3.1 Overview on Different Tunnelling Methods

3.1.1. General

The large number of demanding infrastructural measures realized over the last thirtyyears has brought numerous technical innovations to tunnelling.

Tunnelling methods and technology vary depending on geology, tunnel location,length and geometry, local tradition etc.

In tunnelling there are essentially three different methods of construction:

• Open-cut method of construction

• Cut-and-cover method of construction

• Closed-face method of construction

Tunnelling using the open-cut method of construction initially works vertically fromthe surface of the ground to the floor of the excavation pit. This is followed by theactual tunnel structure, after which the excavation pit is filled in again. Only then doeswork continue in a horizontal direction.

With the closed-face method of construction, also known as underground tunnelling,the tunnel is driven horizontally from a starting shaft (e.g. in an urban area) or a tunnelinset/adit (e.g. in the mountains). The cut-and-cover method is a hybrid method of construction that combines both open-cut and underground methods of construction.Tunnels with the overburden less than half a tunnel diameter are usually built by usingcut & cover methods.

With the closed-face method of construction, various tunnelling methods are possible:

- Tunnelling with mechanical means, ranging from excavators equipped with ripper

teeth, hydraulic rams, and roadheaders to TBMs of various designs. Excavation bytunnel boring machine TBM is always referred to as full-face mechanized tunnelling.



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According to the definition of the French Association of Tunnels and UndergroundSpace (AFTES, 2000), “mechanized tunnelling techniques” (as opposed to the so-

called “conventional” techniques) are all the tunnelling techniques in whichexcavation is performed mechanically by means of teeth, picks, or discs . Within themechanized tunnelling techniques, all (or nearly all) categories of tunnelling machines

range from the simplest (backhoe digger) to the most complicated (confinement-typeshield TBM).

- Sprayed concrete methods of construction, such as Sprayed Concrete Lining (SCL) or New Austrian Tunnelling Method (NATM), Norwegian Method of Tunnelling (NMT),and Analysis of Controlled Deformation in Rocks and Soils (ADECO-RS). TheSCL/NATM and NMT usually involve drilling and blasting; these and ADECO-RS all

belong to the conventional group.

- Special construction methods (pipe jacking, Microtunnelling, Horizontal directionaldrilling, Caissons). The special methods and above-said conventional methods are notwithin the scope of this report.

Tunnels are built today where the public requests them and not necessarily where thegeological conditions would be more favourable. This makes construction technicallymore difficult, more exposed to risks, and more expensive. In most projects, financialfactors and the related scheduling are the crucial elements for any decision which can

compromise both the excavation technique and safety consideration. However, all thetunnelling methods should consistently aim at improving progress, cost, performance,and safety.

3.1.2. Classification of Mechanized Tunnelling Techniques

Also according to AFTES (2000), it is vital to have an official classification of mechanized tunnelling techniques in order to harmonize the terminology applied to themost common methods.

The following Table 1 presents this classification. The table breaks the classificationdown into groups of machines (e.g. boom-type unit) on the basis of a preliminarydivision into types of immediate support (none, peripheral, peripheral and frontal)

provided by the tunnelling technique. To give more details on the different techniques,the groups are further broken down into categories and types.



Table 1: Classification of mechanized tunnelling techniques (AFTES, 20



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From the Table 1, different mechanized tunnelling techniques can be re-listed, with afew relevant definitions provided in the next section:

¾ Machines not providing immediate support:

o Boom-type tunnelling machine (Out of the scope of this report )

o Tunnel reaming machine (Out of the scope of this report )

o Hard rock TBM

¾ Machines providing immediate support peripherally:

o Open-face gripper shield TBM

o Open-face shield TBM

o Double shield

¾ Machines providing immediate peripheral and frontal support simultaneously:

o Mechanical-support TBMo Compressed-air TBM

o Slurry shield TBM

o Earth pressure balance machine (EPB)

o Mixed-face shield TBM

According to Swoboda (1990), the future of tunnel construction will certainly beincreasingly influenced by tunnel boring machines. A combination of excavation withtunnel boring machines and blasting appears to be the most economic solution for thefuture.

In line with the topic of this report, only tunnelling operations with tunnel boringmachines (TBM) will be considered.

3.2 Global View of TBM Tunnelling

3.2.1 TBM Types

A TBM is a complex set of equipment assembled to excavate a tunnel. The TBMincludes the cutterhead, with cutting tools and muck buckets; systems to supply power,cutterhead rotation, and thrust; a bracing system for the TBM during mining;equipment for ground support installation; shielding to protect workers; and a steeringsystem. Back-up equipment systems provide muck transport, personnel and materialconveyance, ventilation, and utilities.

List of main constitutive items:



16

- Front face where the soil is excavated with special tools (shield or cuttingwheel/cutterhead)

- Steering mechanism part with drive engines for forward movement.

- Control mechanism for deviation and inclination

- Removal installation for transporting excavated material through themachine to a separator or directly onto an independent transport system

- Installations behind the working chamber permitting either further soilimprovements (i.e. with rock bolts, shotcrete or injections) or are used for

preliminary investigations

- Support installations within the protection of the shield tail

- Eventually grouting the void at the shielded tail created between the liningand the subsoil.

In addition to the above-said technical classifications of the machines by AFTES(French Tunnelling and Underground Engineering Association), there exist other national classifications, such as those of DAUB (German Committee for UndergroundConstruction) shown in Figure 5, JSCE (Japan Society of Civil Engineers) shown inFigure 6, and SIG (Italian Tunnelling Association), etc.

Figure 5: Tunnelling Machines (according to DAUB)

TM

Tunnelling Machines

TBM

Tunnel Boring Machines

SM

Shielded Machines

TBM

TBM without ShieldTBM-S

TBM with Shield

SM-T

Shielded Machines

with Part Heading

SM-V

Shielded Machines

Full-face

SM-T1 Face without support

SM-T2 Face with partial

support

SM-T3 Face with compressed

air application

SM-T4 Face with fluid

support

SM-V1 Face without support

SM-V2 Face with mechanical

support

SM-V3 Face with compressed

air application

SM-V4 Face with fluid

support

SM-V5 Face with earth

ressure balance support



17

Figure 6: Types of Shield (JSCE, 1996)

Some companies or even individuals also draw out specific classifications. Thefollowing are TBM types, according to Rehm (2006):

• Hydroshield/Mixshield

• EPB-shield

• Hard-rock TBM

- Single/double-shield- Gripper shield

• Shield with partial face excavation

• Micromachines

Range of diameter of TBM manufactured by Herrenknecht AG is shown in the Table 2 below. The world’s biggest TBM was used at the Groene Hart railway tunnel project inThe Netherland 2000-2004, with a diameter of Ø = 14.87 m. This record has been

recently broken by a new EPB TBM with a diameter of 15.20 m, manufactured by thesame company.



18

Table 2: Range of diameter of different TBMs (Rehm, 2006)

Another classification of TBM types and operational modes can be summarized as inTable 3 (Grandori, 2006).



Table 3: TBM types and operational modes (Grandori, 2006)

DSU = Double Shield Universal TBM



20

According to Pelizza (2006), mechanized excavation methods can be briefed in twogroups:

- full face mechanized continuous excavation method, using TBM for the

excavation of tunnels in rock. The main problem is to break the rock;

- full face mechanized continuous excavation method, using mechanizedshields and with counterpressure against the face for the excavation of tunnels in soil above and below the water table. The main problem is thestability of the tunnel as well as the control of the groundwater.

Both the TBM (hard rock applications) and SM (Shield Machine, soft ground) fulfillthe same purpose:

- ensuring systematic and automated subsoil excavation;

- providing an effective protection (the shield) for the labour force at thefront;

- stabilizing the tunnel through quickly closing of the support ring;

- transportation of the excavated material

Shields with Special Shaped Cross-section

Shields with special shaped cross-section are divided into two types: Compound

circular shield (or multi-head circular shields, multi-circular face shield - MFS), andnon-circular shield (Figure 7).

Figure 7: Shields with special shaped cross-section (JSCE, 1996)

Shield with specialshaped cross-section

Compoundcircular face

Non-circular faceshield

Twin circular face

Compound triplecircular face shield

Elliptical face shield

Rectangular face

Horseshoe face shield

Half-circular face



21

Selection of TBM

The tunnelling strategy is based on using different types of TBMs. Each machineshould be able to deal the best with the ground conditions expected. They must allow a

pressure to be exerted by the machine against the ground in front of the tunnel to

limiting ground movement and settlement.The size of the tunnel and the geological conditions of the rock determine the type andthe configuration of TBM that is used. Relevant geological factors for the TBMselection are: grain size distribution, type of predominant mineral (quartz contents),soil strength (cohesion), overburden, heterogeneity (mix ground, weathering), and

piezometric pressure (Kovari et al, 2004).

The effect of unexpected geological conditions can be strongly amplified if the TBMhas been wrongly selected.

3.2.2 Operation of TBMs

Generally, tunnel construction using tunnel-boring machines (TBM) involves threemain processes: excavation, dirt/muck removal, and tunnel support.

TBMs’ key specifications may include: shield diameter, machine weight, maximumtorque (that is needed for the cutterhead rotation under the maximum thrust), machineinstalled power, cutterhead/cutting wheel speed RPM, gripper force, penetration, cutter diameter, number of cutters on the cutting wheel, thrust per cutter, etc.

A distinction is basically made between open-type machines, hard-rock TBMs, slurry-shield TBMs (hydroshields), and earth pressure balance (EPB) tunnel boring machines.Below is the briefing on the operation of several TBM types.

Hard-rock TBMs

The machines for rock are built to advance through a hard material that is usually self supporting, and have tools made for breaking even the hardest rocks. The excavation iscarried out at atmospheric pressure, and the extraction of the material is performed

using trains, trucks or conveyor belts to minimize wear (Figure 8).



22

Figure 8: Unshielded gripper TBM schematic drawing (COE, 1997)

The application of the standard TBM types for long and large diameter tunnels invariable ground conditions would be risky, in particular:

• Open gripper type TBMs are too sensitive to poor rock conditions especially inlarge diameter range;

• Single shield TBMs cannot reach high performances in hard rock and are

sensitive to squeezing ground and face instabilities;

• Double shield TBMs, while can achieve very good performance in good to fair rock, are still sensitive to squeezing ground and to face instabilities.

The extremely difficult geological conditions was a good reason to develop a new typeof TBM, that is the Double Shield Universal TBM (Figure 9) which, starting from amain general design concept, can be configured into different specialized versions tosuit the particular project requirements and geology (Grandori, 2006).



23

Figure 9: Double shield universal type TBM (Concilia, 2006)

Compressed air (Air pressure) TBM

A compressed-air TBM can have either a fullface cutterhead or excavating arms likethose of the different boom-type units. Confinement is achieved by pressurizing the air in the cutting chamber.

Muck is extracted continuously or intermittently by a pressure-relief discharge systemthat takes the material from the confinement pressure to the ambient pressure in thetunnel (Figure 10).

It is possible for TBM to work by air pressure, when the soil itself is nearlyimpermeable against the air. This is only possible in rare cases. In addition, the use of compressed air introduces the risk of a blowout, that is, a sudden reduction of support

pressure on account of rapid loss of air; in this case the air may escape to the surface by leakage through soils pores or by a heaving of the ground mass above the shield.

In recent years, thanks to advances in technology together with increasing reluctance,mainly for medical reasons, to use compressed air working methods, slurry shield and

EPB tunnelling machines have become widely used for tunnelling in unstable groundconditions.



24

a Excavation arm g Tailskin seal b Shield h Airlock to cutting chamber c Cutting chamber i Segment erector d Airtight bulkhead j Screw conveyor (or e Thrust ram conveyor and gate)f Articulation (option) k Muck transfer conveyor

Figure 10: Compressed air TBM - Boom type (AFTES, 2000)

Slurry or fluid support machines (Hydroshield)

The Slurry Shield and the Earth Pressure Balanced shield (EPBS) have been developedin the recent decades for managing the instability of the excavation profile inunfavourable geotechnical and hydrogeological conditions, with challenge externalconstraints (see Figure 11 and 12).

With a Slurry TBM, the unstable ground at the front is supported by liquid mixture(bentonite suspension) under increased pressure generating an even counterpressure. Afilter between the existing ground and the support liquid (i.e. using bentonitesuspension) prevents the liquid from penetrating and disappearing into the ground.Depending on the subsoil permeability, density and viscosity can be varied, pressurecan be regulated by controlling the speed of the delivery and feed pumps.

The excavation is done by a turning cutting wheel. The excavated ground material and

suspension liquid is mixed by hydraulic conveyance via tubes with subsequentseparation of the two materials.

The most important deviating design feature of hydroshields from the slurry shields isthe presence of a compressed air buffer through which the support pressure at the fluidsupported working face is controlled by means of a compressed air regulatinginstallation.



25

Figure 11: Hydroshield/ Mixshield with double-chamber system.c Cutterhead,d Bulkhead,e Air-cushion,f Submerged wall, g Slurry line,h Stone crusher,i

Feeding line,j Erector (Rehm, Herrenknecht 2006)

Figure 12: Typical spoke type cutterhead of the Hydroshield/Mixshield(Hamburg ∅14.2 m, Berlin ∅8.9 m)

1

2

3

4

5 6

7

8



26

EPB - Earth Pressure Balance machines

Instead of a hydraulic/bentonite suspension as in Slurry TBMs, the excavated groundin EPB is used as part of the supporting liquid and forms a ground slurry. This method

requests ground which is homogeneous, soft and cohesive (see Figure 13 and 14).

If the water content is too low or if small particles are absent in the grain sizedistribution, they must be added artificially (bentonite, polymers, foam). This is calledsoil conditioning. In this case, the environmental compatibility of the material for landfill purposes must be taken into consideration.

EPB machine has the technical advantage compared to the Hydro-Shield that aseparation plant is not required, hence - space and cost for these systems areunnecessary.

Figure 13: Shield machine - EPB technique.c Face,d Cutterhead,eWorkingchamber,f Bulkhead, g Thrust cylinder,h Screw conveyor,i Erector,j Segments

(Rehm, 2006)

8

2 3

4

5

6

7

1



27

Figure 14: EPB TBM ∅ = 9755 mm used for Botlekspoort Tunnel project 1999-2000(Rehm, Herrenknecht 2006)

The original single chamber design of the traditional Slurry shield was developed into

a two-chamber system (Mixshield) in Germany by the companies Wayss& Freytag andHerrenknecht in the 1980s. The mechanical concept of the Mixshield is a very uniquetunnel boring machine considering it size and type, which allows a conversion betweenthe operation modes EPB shield and Hydro shield in a very short time.

The geological range of application for slurry shield and EPBM is given in Figure 15.

Figure 15: Relevant grain size distribution for EPB and Slurry TBM drives



28

Mixed-face shield TBM / “Universal” TBM

Modern technology has enabled us to design mixed (versatile) machines able to dealwith different (even extremely heterogeneous) soils during a single project, which can

operate both as EPB machines or Hard Rock TBMs with a few modifications to thecutting wheel and extraction system. Changeover from one work mode to another requires mechanical intervention to change the machine configuration. The universalmachines are best used with the universal ring.

The biggest challenge that the tunnelling industry is going to face in the newmillennium is related to the design and the use of large diameters TBMs for theconstruction of long road and railway tunnels.

One point deserves mention is that, because of the magnitude of the risk associatedwith rock mass conditions, a new double shield universal TBM design has been

realized. However, DSU TBMs could be uneconomical where systematic treatment of the face is required for the whole length of the tunnel; in this case the use of an EPBmachine equipped with advanced conditioned and fine compensation systems might bemore convenient (Concilia, 2006).

3.2.3 Conventional Tunnelling Versus TBM Tunnelling

TBM tunnelling is characterized by a less aaddaa p pttaa b biilliittyy ttoo ggeeoollooggyy,, b beetttteer r p pr r ooggr r eessss r r aatteess,,

p poossssii b bllyy ccoonnttiinnuuoouuss ttuunnnneelllliinngg,, aanndd r r eellaattiinngg ttoo lloonnggeer r ttuunnnneellss.. More and more tunnel projects are going to be mined by the safety TBM techniquewhich in the past would have been excavated by the conventional method with all itsuncertainties for the personnel.

The advantages and disadvantages of using a TBM include the following:

Advantages of using a TBM Disadvantages of a TMB

• Higher advance rates

• Continuous operations

• Less rock damage

• Less support requirements

• Uniform muck characteristics

• Greater worker safety

• Potential for remote, automated

operation

• Fixed circular geometry

• Limited flexibility in responseto extremes of geologicconditions

• Longer mobilization time

• Higher capital costs



29

Concilia (2006) stated that the mechanised method of excavation can be 4 times (smalland medium diameter tunnels) faster than D&B, providing the correct machine has

been selected.

Although any tunnel excavation will influence the immediate surroundings to someextent, the aim of mechanized tunnelling which includes excavation and supportinstallation processes is to avoid and minimize stress relaxation. A comparison on thegeneral aspects between conventional and mechanized tunnelling could be tabled asfollows (Assis, 2006):

Conventional Tunnelling Mechanized Tunnelling

• Geometry Flexibility

• Geology Flexibility

• Contractual Flexibility

• Political Flexibility

• Lower costs for short tunnels andcheaper labour

• Lower impact to ground

• Higher and more constantquality (industrial process)

• Lower load to workers

• Safer

• More accurate costs andschedule

Table 4 below gives another comparison between conventional shotcreting measuresand mechanical drives in terms of constructional engineering and operational terms.



30

Table 4: Comparison of major criteria for shotcrete tunnelling methods and TBMs(after A. Haack, 1996)

Itemno.

Phase Assessment criteriaShotcretetunnelling

methodTBM

1 Supporting agent in face zone variable safer

2 Lining thickness variable constant

3 Safety of the tunneling crews lower higher

4 Working and health protection lower higher

5 Degree of mechanization limited high

6 Degree of standardization conditional high

7 Danger of break higher lower

8 Construction time - short tunnel shorter longer

9 Construction time - long tunnel longer shorter

10 Construction cost - short tunnel lower higher

11

Construct

ion phase

Construction cost - long tunnel higher lower

12 Tunnel cross-section variable constant

13 Cross-section form as desired generally circular

14

Operation

al phase Degree of utilization of the drive-related tunnel cross-sections

generallyhigher

generally lower

With respect to the question of comparative costs between conventional/hand miningand mechanized tunnelling, Sauer (2004) made a diagrammatic representation asshown in Figure 16. The diagram shows that conventional tunnelling is more costeffective than mechanized tunnelling for the cases of short tunnels (< 2.4 km), shaftsand tunnels with changing geometry, and/or substantially changing geotechnical

behaviour. There is an overlapped area where hand and mechanical mining may beequally considered and where a dual design is recommended. With tunnels longer than3.2 km, Sauer showed a little difference of construction costs between hand miningand mechanized tunnelling.



31

Figure 16: Tunnel cost of Mechanized Tunnelling (MT) versus Hand Mining (HM)over tunnel length (Sauer, 2004)

In addition, according to Wagner (2006, oral consultation), the statements on thetunnel cost must be more related to ground conditions. It is impossible to establish ageneral rule on the cost, because it relates to geological conditions and to work

progress (i.e. advance per day or per month). The tunnel costs may also need to beestimated using special TBM cost estimating software and cost database.

Below Figure 17 shows a comparison of excavation and ring installation times

between the TBM “serial” tunnelling and TBM “continuous” tunnelling. The firsttechnique uses traditional ring type; the second uses unified rings, featured bysimultaneous excavation and ring erection. The erection time of the first is twicelonger than the second.

Figure 17: Modes of tunnelling with unified rings (Wagner, 2006)

""SSEERRIIAALL"" TTUUNNNNEELLLLIINNGG CCOONNTTIINNUUOOUUSS TTUUNNNNEELLLLIINNGG

EERREECCTTIIOONN TTIIMMEE

TTUUNNNNEELL LLEENNGGTTHH

EEXXCCAAVVAATTIIOONN TTIIMMEE PPEERR RRIINNGG IINNSSTTAALLLLAATTIIOONN TTIIMMEE PPEERR RRIINNGG

EERREECCTTIIOONN TTIIMMEE

RRIINNGG 33

RRIINNGG 22

RRIINNGG 11

RRIINNGG 33

RRIINNGG 22

RRIINNGG 11

TTEE,,CC == 00,,55 .. TTEE,,SS



32

Given the Hai Van Pass Tunnel in Vietnam (2000-2005) as an example; this is adouble lane highway tunnel, the width is 11.9 m, excavation area is 95.2 m2, openingarea is 73.3 m2, the length 6.2 km, excavated in accordance with the principles of

NATM. If a combination of TBM and conventional excavations had been done, thenthe progress would have been faster 2 ÷ 3 times. The scheme for this combinationwould be: both sides are excavated with NATM in lengths of 50 ÷ 100 m, so that themax. conventional length is about 250 m, and the remaining main section is drivenwith TBM. It may be interesting if the same scheme is considered for the upcomingtunnel on the same highway No. 1A in Vietnam, namely Deo Ca Tunnel.

3.3 Critical Cases of TBM Excavation

Although the conventional tunnelling holds certain critical cases, they will not beconsidered in details in the present report. Other special methods of tunnelling such asopen trenches, cut-and-cover structures (direct and inverse excavation), door-framemethod, and immersed tunnels (caisson and door-frame methods), etc. are also beyondthe scope of this project. However, it is possible to name a few of difficult conditionsin conventional tunnelling such as: heavy groundwater leakage/high pressure inflow,very low overburden, soft ground, mixed face, swelling, squeezing, and rock burst, etc.

It is recognized that the TBM performance is influenced by the rock mass quality, theselected machine type and the tunnel diameter. Advances in TBM technology andreliability have resulted in bored tunnels being successfully driven through groundconditions historically considered difficult. However, critical cases of TBM excavationfrom which risks emanate do not disappear. During excavation, the situation can

become critical at any minute, meter, and under any circumstance.

3.3.1. Risk Management for Tunnels

It is well known, that tunnelling is not a risk-free technology. Tunnels are regarded asso called “heavy risks”, because each tunnel is a specific unique project on its own in aunique combination of ground / soil. The “right” construction method with the “right”experience parties involved are crucial for the success. The main most important factor however, the geology, is only known to a limited extent. Any accident duringconstruction as well as in use provokes a substantial interruption and often a standstilltill the problems are solved (Andreossi, 2001).

The construction of tunnels and underground works are affected by potential risks notonly for the different active Parties/main Actors (Owner/Client, Consulting Engineers,

Contractor, Supplier), but also for the Public, especially in urban areas. Tunnelling projects must now consider numerous underlying political and environmental factors



33

which add to the overall complexity of a given project (IMIA, 2001). This is inconformity with the statement by Parker (2005), that “realistically, not all risksassociated with complex construction projects can be entirely avoided or mitigated”,which calls for the need of risk management.

According to its definition risk has two components: probability of occurrence w andamount of damage D. In a quantitative appraisal the product of these two factorsdefines the risk: R = w x D.

In other words:

Risk = Probability x Impact

= Likelihood x Consequences

= Probability of Happening x Cost of Event

Figure 18 shows the concept of reducing an initial risk by reducing its probability andimpact. It is clear that residual risks are unavoidable and they should be shared amongthe Parties and systematically controlled by countermeasures.

Figure 18: Concept of reducing initial risk by reducing its probability and impact

Several kinds of risks include (ITA, 2004):

- significant cost overrun risk

- work delay risk

- environmental risks

- risk of spectacular tunnel collapses and other disasters (potential for large scaleaccidents during tunnelling work)

- risk of damage to a range of third party persons and property in urban areas, (a particular concern with heritage designated buildings)

initial

risk

likelihood or probability

c o n s e q u e n c e s o r

e f f e c t / i m p a c t

NOT ACCEPTABLE

ACCEPTABLE

residual risk



34

- risk of public protests, caused by the problems of tunnelling projects

“Risk management” is the overall term which includes risk identification, risk assessment, risk analysis, risk elimination and risk mitigation and control.

Risk management for tunnels is now routine for major projects worldwide. Tunnelconstruction imposes risk not only on all parties involved, but also on those notdirectly involved (note, that third parties - person or companies - have become muchmore “claims conscious”). Traditionally, risks have been managed indirectly throughthe engineering decisions taken during the project development. However, ITAGuidelines (2004) now recommend Systematic Risk Management Techniques instead.And through the use of a robust and transparent Risk Management Plan (RMP)adopted from the early design stages to the construction and operation phases, mostrisks can be effectively managed.

Risk management tools include (ITA, 2004):- Fault tree analysis

- Event tree analysis

- Decision tree analysis

- Multirisk

- Monte Carlo simulation

In a broader context, we could mention a Code of Practice for Risk Management of Tunnel Works, drafted by BTS (British Tunnelling Society) in association withInsurers, such as ABI (Association of British Insurers), IMIA (InternationalAssociation of Engineering Insurers), and ITIG (International Tunnelling InsuranceGroup). This is a joint effort to face the more demanding challenge of future tunnelling

projects. It is hoped that the risks will not be solely transferred to the insurer, but befairly shared between the Parties involved.

An international version of the Code is being prepared by BTS and likely to becompleted soon. Its project stage basis is worth mentioning: 1. project development

stage, 2. construction contract procurement stage, 3. design stages, and 4. constructionstage. Of which, in the construction contract procurement stage, three highlights are: i)the use of FIDIC (International Federation of Consulting Engineers), ICE (Institutionof Civil Engineers), National or Proven Form of Contract; ii) including of GBR (Geotechnical Baseline Report) in Contract Documents, and also in SubcontractDocuments; and iii) including risk clauses in contract. The risk of unforeseen groundconditions (differing site conditions) and contractual claims cannot be overlooked;these can be administered fairly with the help of Disputes Review Board (DRB).

Below is given a brief introduction to a cost-risk estimating procedure (CEVP) and adecision making tool (DAT) in tunnelling.



35

The cost-risk estimating procedure CEVP® (Cost Estimate Validation Process) recentlydeveloped by the Washington Department of Transportation (WSDOT). CEVPdevelops a probabilistic cost and schedule model to comprehensively and consistentlydefine the probable ranges of cost and schedule required to complete each project, byincorporating uncertainty (uncertainty includes both risk and opportunity) (Reilly,

2005) (Figure 19).

Figure 19: Future costs are a “range of probable costs” (Reilly, 2005)

Because risks are explicitly defined, a risk management plan can be quantified earlier.This allows significant management and control of cost and schedule earlier in a

project and allows a more explicit communication of cost and schedule (and changes

thereto) with the public and key political decision makers.

Obviously, it is desirable to use some decision making tools in tunnelling like DAT(Decision Aids in Tunnelling) to make more rational, informed, and effective decisionsin tunnel design and construction. The software DAT is the product of a long researcheffort by: MIT (Massachusetts Institute of Technology, USA), EPFL (l’EcolePolitechnique Fédérale de Lausanne, CH), and GEODATA - Turin (I) for estimatingthe cost and duration of the construction of an underground project. The mostimportant element of DAT is the possibility to consider diverse sources of geotechnicaland construction uncertainties and variabilities (Grasso et. al. 2001, 2002).

In Figure 20, the deterministic estimation and result of DAT simulations of a projectduration and cost are visibly compared.



36

Figure 20: Scatter plots of a project duration and cost (after Grasso, 2001)

Both RMP and DAT have been successfully applied in recent years to a series of important deep and long tunnel projects like the California high-speed rail, the Pajaresand Guadarrama high-speed railway tunnels in Spain, the new Lyon-Turin high-speedrailway link (Grasso, 2006).

Experience with risk management for the Copenhagen Metro in Denmark (opening inturn 2002, 2003 and 2007) (ITA, 2004):

◊ The Contract defined the construction risk assessment work to be carried out bythe Contractor. There were general requirements for all the construction risk assessments to be carried out for all construction sites and some further requirements to the construction risk assessment for the TBMs.

◊ The TBM construction risk assessment had to start immediately after signing of the Contract with an assessment of the conceptual design followed by anassessment of the detailed design with the purpose to contribute to the design of the TBMs. Furthermore, risk assessment of the TBM operation was carried out- providing input to the operation procedures.

◊ Risk identification and management (applied for the “tunnel project xyz”):



37

• Installation risk resulting from TBM rotation

• TBM advance pressure

• Twisted thrust shoes

• Rigid erector hydraulics

• Transport conditions

• Sequence of installation

• Eccentricity of thrusters

• Sectional tension forces

Risks are related to both TBM tunnelling in soil (soft ground, e.g. urban area) and toTBM tunnelling in rock, therefore below is shown a number of critical cases that bring

about risks.

3.3.2. Critical Cases of TBM Tunnelling in Soil

Basic soil classification

Ground categories are broken down roughly according to the following table:

Table 5: Simple soil classification for construction purpose

Hard rock Soft rock Soft soil

(without cohesion)Soft soil

(with cohesion)DolomiteLimestoneSandstoneGraniteBasaltLavaGneissQuartzite

MarlHard claySlateDolomite

Sand, fine gravel,gravel,coarse-grained,stonesFlowing ground =soil with high water content

Expansive or swelling groundsuch as clay-stones,anhydrite rock incontact with water,silt

Generally, in soft ground, majors concerns are opening stability and control of displacement field. Soft ground tunnelling is likely dominated by failure andadmissible displacement criteria. Ground conditioning (improvement andreinforcement) might play an important role. In consolidated clay, the optimization of values and quantities of the slurry pressure and grouting pressure is required for TBMtechnology.

In urban environment, major concerns are related to: shallow overburden, existence of nearby structures, foreign objects inside the ground, constraints for alignment,



38

restrictions for auxiliary works, and high visibility of damage. Ground conditions arenormally challenging, characterized by recent weak geological formations near theground surface, by frequently changing conditions due to the occurrence of lenses,layers, boulders, etc., and by presence of ground water above the tunnel or crossing thetunnel profile. Kovari et al (2004) listed the following specific features of metropolitan

areas:

• Shallow overburden: Low overburden may be combined with a large tunneldiameter to create ground deformations (settlements) and collapse up to surface(Figure 21).

Figure 21: Full face mechanized excavation of shallow tunnel (Maidl et al. 1996)

• Existence of nearby structures: The next structures may consist of buildings,roads, railroads, bridges, underground networks, subways, etc. (Figure 22). Thesensitivity of these structures to ground settlements as well as the potentialdamage to ground collapse may vary within extremely wide ranges. Surfacemonitoring in urban environment is fundamental to control the effects and the

potential damages on pre-existing buildings, utilities and infrastructures. For example, in the first stage of settlement assessment, if the predicted settlementfrom bored tunnels is less than 10mm and the predicted ground slope is lessthan 1/500 (equivalent to damage risk category 1 as defined by Rankin, 1988),then buildings are not subject to further assessment.



39

Figure 22: Influence of a TBM drive on the neighbour buildings (Gruebl, 2006)

• Foreign objects inside the ground: The presence of frequently hiddensubterranean obstacles is also one of the specific features of urban tunnellingusing TBM’s. These may include historical wells, ground anchors, sheet-piles,erratic blocks, archeological artifacts, abandoned utilities such as for gas andsewage, but also tree trunks, artificial fillings, etc.

• Constraints for alignment: Selection of both horizontal and vertical alignmentgenerally meets with constraints. The tunnel is usually driven in public groundunder main roads or streets. But it is not always possible to avoid under-passing

buildings, roads and other structures, and this may cause various difficulties.For example, land acquisition costs would be very high and the foundations of the existing buildings would create complications during construction. Figure

23 shows the Brisbane North-South Bypass Tunnel alignment within the citycentral area.



40

Figure 23: Brisbane North-South Bypass Tunnel, Central Connection Option 7(SKM Connell Wagner JV, 2005)

• Restrictions for auxiliary works: It is practically important to note the seriousrestrictions when selecting places of attack (launching shaft, access to TBM)and planning material transport from and to the construction site. Other restrictions include sinking drill holes for explorations, for ground water controlor ground consolidation.

• High visibility of damage: In the urban environment damage to buildings androads has a high visibility. The risk aversion is very pronounced, which maylead to a strong opposition to further underground projects in towns or even

elsewhere. The loss of public confidence in the technology can be looked uponas a kind of damage.

Other difficult cases (in a general nature, after JSCE, 1996):

- Underground tunnel connection: Two shield tunnels can be connected head-on,or one tunnel is connected into the side of the other tunnel. For head-onconnection, auxiliary measures such as chemical grouting, high-pressure jettingand mixing method or ground freezing are generally used. For side-by-sideconnection, reinforcement of the existing tunnel must be studied to prevent any

damage to it.- Underground space enlargement: Construction of an underground station

between two tunnels, a space for shield machine assemble or undergroundspace establishment, a branch-off tunnel or connection of a tunnel with someangle. Because the ground is already loosened by the preceding tunnelconstruction work, the ground shall be stabilized by auxiliary method asrequired. The tunnel shall then be carefully enlarged by excavating a partialface and by supporting the ground with steel supports or special segments.



41

Kovari et al (2004) then summarized the main features permitting safe and economictunnelling in soft ground under urban conditions using TBM´s with slurry or EPB typeof face support as follows:

• Efficient TBM technology

• Reliable design procedure

• Improved methods of conditioning

• Advanced grouting technology

• Reliable risk management

Practically, Cross London Rail Links (Crossrail, U.K.) can be referred to as a largetunnel project in urban area today. The project has plans to ensure that the tunnel

boring machines are performing as required, the TBM parameters together with theinformation from the ground movement monitoring need be relayed to a tunnelmonitoring and settlement control room. This will be in addition to the contractors’monitoring arrangements and will be in place and operated throughout the tunnellingactivity. The control room will have displays of real time surface, subsurface andtunnel movement monitoring together with TBM tunnel progress and TBM

parameters.

3.3.3. Critical Cases of TBM Tunnelling in Rock

Some of the (obvious) high-risk factors (multiple unexpected events) that TBMtunnels may suffer from include (Barton, 2006):

• significant fault zones

• adversely oriented planar clay-coated joints

• very weak rock, or very hard massive rock (high UCS rocks)

• very abrasive rock

• very low stress, very high stress

• exceptional stress anisotropy

• highly fractured or karstic zones with high volumes of stored water (severewater inflows)

• high permeability

In addition, Barla & Pelizza (2000) wrote, that important or difficult groundconditions for TBM tunnelling include boreability limits (when boring through rocks

with very high strength), instability of excavation walls (a clear limit for open typeTBMs), instability of excavation face, fault zones and squeezing.



42

It is hoped that the majority of the limit conditions will be coped with by adoptingspecial methods and procedures of advance.

Below are selected and explained to more details some of the above high-risk factors.

9 Significant fault zones

The cause(s) of a tunnel collapse or TBM cutter-head blockage (machine is trapped) ina tunnel are usually clear to the tunnelling engineer only after they have happened.Fault zone stoppages and difficulties/delays in making drill-and-blast by-passes for TBM/cutterhead release may eventually lead to the abandonment of TBM itself or abandonment of TBM option. So, before the event it would often be necessary to beexceptionally pessimistic to have foreseen the ‘unthinkable’. The ‘unthinkable’ is oftenthe combination of several adverse factors, which separately are ‘expected’ thoughserious events, but when combined are, quite logically, ‘unexpected events’ (Barton,

2006).Figure 24 shows a TBM stuck in a bulk of caving-in materials; this implies, that"risky" means to free up the trapped TBM cutter head or shield.

Figure 24: By-pass situation for the double-shield (11.7m) TBM at Pinglin tunnel,Taiwan (Shen et al. 1999)

Short sections of crushed shear zones with clay and gouge material may cause serioustime delays for TBM excavation. Spiling rock bolting is very efficient under suchcircumstances, provided the fully grouted rebar bolts can be placed efficiently, whichrequires proper drilling equipment. Figure 25 exhibits a situation of TBM pull back and liner disassembly due to debris flow from a fault gauge zone.



43

Figure 25: TBM pull back and lining removal to overcome the debris flow (Oggeri,2006)

Figure 26 shows the TBM utilization while boring through a fault zone. The utilizationfactor is an important parameter, and it varies according to the actual geologicalconditions.

Figure 26: Geological conditions and productivity (Concilia, 2006)



44

Pre-grouting has been proposed by Barton as a measure to reduce risks, because pre-injection can increase Q index of the rock mass.

It is well known, that the Q-values (the rock tunnelling quality) are estimated from the

following expressions:RQD Jr Jw

Q = x xJn Ja SRF

0TBM 10 9

RQD Jr Jw SIGMA 20 qQ = x x x x x x

Jn Ja SRF F / 20 CLI 20 5θ σ

where:

- RQD = Rock Quality Designation, is characterization of the degree of jointing;

- Jn = number of joint sets.

- RQD/Jn = quotient representing a crude measure of relative block size ;- Jr = rating for the roughness of the least favourable of the joint sets or filled

discontinuities;- Ja = rating for the degree of alteration or clay filling of the least favourable

joint set or filled discontinuity.- Jr/Ja = quotient representing the roughness and frictional characteristics of the

joint walls with or without filling materials. It is crude measure of inter-block shear strength;

- Jw = joint water reduction factor;- SRF = Stress Reduction Factor;- Jw/SRF = quotient representing a crude measure of active stresses;- RQDo = RQD (%) measured in the tunnelling direction;- SIGMA = rock mass strength estimate (MPa) found from a complicated

equation including the Qo value measured in the tunnel direction (the same asthe six first parameters);

- F = average cutter load (ton, ~10kN ) through the same zone, normalised by20 tons;

- CLI = Cutter Life Index;- q = quartz content in percentage terms, %;- σθ = induced biaxial stress on tunnel face (MPa) in the same zone, normalised

to an approximate depth of 100 m.



45

Pre-injection/pre-grouting may cause moderate, individual effects to every parameter (6 parameters) contained on the first expression, thus increase Q index of the rock mass.

The concept of multilayer pregrouting is represented in Figure 27. The first grouting

operation is to create around the tunnel an outer reduced-permeability zone using"blocker" grout. The second grouting is to make an inner permanent strengthened, low permeability zone using stable ultra/microfine cementitious grout. The third is anextended, strengthened, low permeability zone ahead of the excavation face.

Figure 27: One of ELKEM’s Multigrout concepts

The idea of reducing risks by pre-grouting also lies behind the fact that, the relativetime for tunnelling and the relative cost of tunnelling normally decrease in accordancewith the increase of rock classes quality. So, if Q could be detected before tunnelling,and if Q could be improved during tunnelling, then both time and cost could bereduced accordingly (Figure 28).

Figure 28: Relative time expenditure (left) and relative cost (right) of tunnelling in

relation to Q value



46

Finally, Barton drew out the following comments on the risk to TBM tunnelling fromfaults:

- High risk factors are often combined in an ‘unexpected’ combination whenTBM get stuck;

- Risk can be reduced by appropriate use of standard techniques (geologicallogging and rock mass characterization, core logging, hydraulic testing, seismic

profiles between holes);

- When tunnel depth is great, each of the above require ‘extrapolation’ and risk increases, making probe drilling (even) more important;

- Barton stated that: “Don’t automatically assume that long tunnels need TBM -this will also reduce risk!” The assumption that TBM go faster than drilling-and-blasting in long tunnels introduces several increased risks:

a) adverse rock quality statistics (extreme-Q-value problem) b) need ‘central’ rock qualities to improve TBM deceleration (negative

gradient) of the penetration rate and advance rate with increased tunnellength or time of measurement

c) less favourable ‘problem solving’ conditions for the contractor in TBMtunnel

- Seismic velocity probing needs careful correction for stress/compaction effectsas the longitudinal wave velocity VP in front of TBM may increase without rock quality improvements (e.g. the deeper rock does not always mean better quality,

but just more highly stressed);- A way to improve effective rock quality and control water, and therefore to

reduce risk, is to (try to) perform pre-injection ahead of the face.

However, it should be noted, that Blindheim (2005) already recommended the QTBM-system not be used. In addition, Palmstrom and Broch (2006) also think it is not likelythat Q is suitable to express the effects of pre-grouting. They went further that QTBM iscomplex and partly misleading and is not recommended for use in its present form, i.e.to allow estimates of penetration and advance rate for TBM (Figure 29).



47

Figure 29: Suggested relation between penetration rate (PR), advance rate (AR) andQTBM values (Barton, 1999b)

9 Very high stress

Serious problems of high rock stress phenomena in TBM tunnels involve intense rock

spalling in hard and massive rock, which causes significant safety hazards (e.g. duringcutter change) and delays in work progress (e.g. loss of support for the TBM gripping

pads). Rock stress may also lead to occurrences of mild buckling of schistose rock.

It is important to be able to perform rock bolting efficiently immediately behind thecutter head in order to maintain work safety and firm gripping for continued boring.The need to handle rock stress problems in bored tunnels has been due to rapiddevelopment and application of tunnel boring. The experience on this issue should beapplied from the planning stage of TBM projects where such problems may beencountered, and the well preparedness should be highlighted. In massive and strongrocks the spalling can occur in a concentrated and intense manner in bored tunnels,

therefore utilizing TBMs with an open configuration and not shielded TBMs could bean advantage.

9 High volumes of stored water, under pressure

The only available tunnelling technique that can keep the ground water in-leakage near zero, is the Earth Pressure Balance Machine (EPBM), full face mechanical excavationusing a pressurized shield and gasketed concrete segment installation. Such machinesare for soil excavation and are limited to shallow depths (typically less than 15 meters)(Garshol, 2003).



48

In hard rock tunnelling this alternative is not available, even if a TBM and concretesegments are used for the excavation and support. Without pre-injection the leakagevolume could locally become far too large, between the time of exposure and the timeof segment erection and efficient annular space backfilling. With a serious local water inrush at hand, such segment handling and grouting would also be very difficult.

Environmental restrictions are also a part of TBM tunnel excavation projects. Evensuch tunnelling may require a strict ground water control, because of the normal

potential consequences on the ground surface.

There are two ways of handling water inflow problems:

1. Pumping out of the water

2. Injection

There are clear limits as to the quantities of water that can be pumped through pipes, or

that can be handled by gravity drainage systems, provided that reasonable practical andeconomical frameworks are applied. The limitations are even more pronounced whenconsidering the face area. Tunneling on a decline will experience problems already atinflow rates of only 1 to 2 m3/min. Water at a high static head may cause water jetsspraying the whole face area, causing very difficult working conditions, especially atlow water temperatures. If inflows have already occurred (through cracks and joints),

post grouting is very difficult, costly and often unsuccessful, especially at high pressure.

To take advantage of spiling rockbolts and to execute pre-injection, it is an obvious prerequisite to be able to drill the necessary boreholes in the right positions and at the

correct angle. In drill and blast excavation this is simple, but in TBM projects it hasrepeatedly turned out to be difficult. The owners should accept only bids that containthe drilling method proposed by the contractor. The drilling method should be sortedout before start of the TBM operation (Figure 30 and 31).

Figure 30: Tailor made hydraulic drilling equipment mounted on hard rock TBM(Garshol, 2003)



49

Figure 31: Borehole length and net coverage per grouting stage, plan view (Garshol,2003)

In short, a well planned use of probe drilling, pre-injection locally and pumping willnormally be the optimum solution. The risk of major water inrushes can be virtually

eliminated.

9 Squeezing rock conditions

Excessive rock pressure may cause the failure of the tunnel support resulting in largerock deformations, with the tendency to reduce the cross-section of the opening. This

phenomenon is referred to as squeezing rock behaviour. Low strength and highdeformability of the rock as well as the presence of porewater pressure facilitatesqueezing. The following rock types are specially prone to developing large pressureand large deformations: altered gneiss (chemically altered/metamorphic igneous

rocks), schist, phyllite, serpentine, shale, clay, mudstone, tuff, and certain kinds of flysch (Kovari, 1998).

Mechanized excavation (use of Tunnel Boring Machines) in squeezing rock conditionsis characterized by a certain degree of difficulty. It is generally agreed at the presentstage that experience and technology have not progressed far enough to recommendwithout some reservations machine excavation in such conditions. The major difficulties can be listed as follows:

- Instability of the face;

- Relative inflexibility in the excavation diameter;

- Problems with the thrust due to reduced gripper action, for gripper typemachines;

- Difficulty to control the direction of the machine, in soft or heterogeneous ground.

Instability of the face may be a problem only when severe squeezing conditions exist,which exert important face extrusion that could be difficult to be controlled. It is alsodifficult to anticipate precisely the type and magnitude of tunnel convergence (i.e. thereduction in size of the opening in course of time). With a slow advance rate, the

danger of TBM blockage in a squeezing zone (i.e. a fault zone) is increased. Stoppageof the TBM can be brought out by a number of factors such as inflow of water,



50

advancing face, overbreak, or machine breakdowns. In the worst case as such, with acontinuing displacement the machine may be squeezed, leading to difficulty or impossibility to restart the machine.

The type of machine, i.e. shielded or not shielded TBM, will be selected based on the

degree and extent of squeezing rock conditions along the tunnel length. Both shieldedand open TBMs may be sensitive to rapid or large convergences plus wall instabilities,causing the problems of support installation and gripping. Therefore, increasing thediameter of the cutter head (overcutting) is often foreseen, so that the gap between theshield and the excavation contour from the usual value of 6-8 cm can be adjusted to15-25 cm (Figure 32).

Mediate squeezing conditions could be coped with by TBMs that are specificallydeveloped to accommodate some radial deformation of the tunnel perimeter as themachine advances (Barla & Pelizza, 2000).

Figure 32: Solution for radial overcut by increasing the excavation diameter -Controlled overcutting device

Squeezing ground behaviour is characterized by the occurrence of large rock pressurewhich may lead to the failure of the lining. Therefore, there have been attempts to limitthe loads on the lining ring by means of installed strain elements. The plasticallydeformed joints cannot be sealed watertightly. Loads can also be limited through theuse of substances of a defined firmness which collapse when a certain resistance limitis passed. These substances are either fitted on the outside of the segment or added tothe grouting material.

In another development, for the squeezing type of deformation phenomenon thefollowing are possible counter-measures for mechanised excavation (Grasso, 2006):

- plane head;

- overcutting;

- requalification of the rock mass ahead;- bolts in shotcrete layer 1 (Open TBM);



51

- short shield/absent/ with loopholes (Open TBM);

- conical shield (Double shield);

- bentonite injections (Double shield);

- deformable support (Open TBM);- extended gripper surfaces (Open TBM)/ thrust on segments (Double shield);

- shotcrete in layer 2 (Open TBM).

3.3.4. TBM Tunnelling in Mixed Face Conditions

For a specific long tunnel project with changing geological conditions in different

segments/sections, the tunnelling can be completed in phases using TBMs. Successfuland economical completion of each section of tunnel requires the proper choice of TBM type and ground support, based on the ground conditions expected. Severaldifferent TBM types with various ground support methods may be needed toaccommodate the various ground conditions.

Development of TBMs during the past over 20 years has brought about so-calleduniversal machines (polyshields, multipurpose shield, Figure 33), used for both softground and hard rock. The continual improvement of various extraction techniqueshave led to machine types capable of penetrating more heterogeneous subsoil, that isrespectively a mixture of soft soils, unconsolidated ground and rock, thereby

enhancing their rather limited flexibility.

Figure 33: Polyshield machine, EOLE Lot 35 B, Paris, France (Wagner, 2006)



52

To end up this section, it is fair to cite the following statement by Barla and Pelizza(2000):

“The unfavourable conditions can be produced by either a rock mass of very poor

quality causing instability of the tunnel or a rock mass of very good quality (i.e.

strong and massive rock mass) determining very low penetration rates. However,it is to be observed that when using the full face mechanized excavation method,

the influence of the rock mass quality on the machine performance has not an

absolute value: the influence is in fact to be referred to both the TBM type used

and the tunnel diameter”.

3.4 Ground Reinforcing

3.4.1. General

This part is devoted to the problems of face stability and ground reinforcement for TBM drives in cohesive and cohesionless soils.

3.4.1.1 Face Support

Face stability is fundamental to avoid failure. In closed shield tunnelling, there arethree main ways to support the face: by compressed air, by slurry, and by excavated

soil (EPB) (Figure 34).

Figure 34: Face support in closed shield tunnelling (Kovári et al, 2004)

3.4.1.2 Failure Mechanism

Ground and groundwater pressures at a workface can be unbalanced: If the shieldadvancement rate and muck discharge rate are not synchronized in an EPB shield or aslurry shield, the pressure inside the chamber becomes different from the ground and

groundwater pressure, at the face become unbalanced. If the pressure in the chamber is



53

smaller than the ground pressure, surface settlement occurs. In cases of contrary,ground heave occurs.

Explaining and predicting face stability by statical calculations has already beenaddressed by a number of authors, of which some are mentioned here. Upper and

lower bound 2D solutions for clays (limit equilibrium solutions) can be founded in thework of Davis et al (1980). Limit-state-design-based solutions have also been proposed by Leca and Dormieux (1990) for sands. A three dimensional failure schemeconsisting of a soil wedge (lower part) and a soil silo (upper part) has been given byJancsecz and Steiner (1994). Anagnostou et al (1994, 1996), based upon the silo theoryaccording to the tridimensional model of sliding mechanism proposed by Horn (1961),

provided a good understanding of the mechanics of face failure and determined facesupport pressures when using a bentonite slurry support as well as EPBM.

In the following only two methods will be briefly introduced, i.e. Leca and Dormieux(1990) and Anagnostou and Kovari (1994, 1996).

a) Limit-state-design-based solutions by Leca and Dormieux (1990)

Leca and Dormieux (1990) proposed upper and lower bound solutions for the facestability of shallow circular tunnels in frictional materials (sandy soils) (Figure 35).The question of determining the retaining fluid pressure to apply to the tunnel front is athree-dimensional problem, and was studied by using limit state design method. Suchretaining/supporting pressure σT can be achieved by using compressed air, bentoniteslurry or earth pressure (EPB shield).

Figure 35: Simplified geometry for the front stability of a shallow tunnel(after Leca and Dormieux, 1990)

Both safety against face collapse and blow-out were considered based on the motionmechanisms of rigid conical blocks in front of the face, then a failure criteria was

proposed for a cohesive and frictional soil.

A

A

σC = unconfinedcompression strength

σT

σS

HC

D

P

σS

' '

'

cos2

1 sinC

c φ σ

φ =

−

σT

Section A-A

σS = surcharge

= unit wei ht of soil

P = unsupported span

σT = retaining pressurec' = cohesionφ' = frictionangle



54

Three failure mechanisms have been considered namely MI, MII and MIII, which areshown in Figure 36, with the assumption that the unsupported span behind the face P iszero. MI and MII are failure mechanisms due to the collapse of one conical block andtwo blocks, respectively, whereas MIII refers to blow-out failure in case of veryshallow tunnels bored in weak soils with the pressure σT becoming so great that soil is

heaved in front of the shield.

Figure 36: Conical failure mechanisms (a) MI, (b) MII and (c) MIII (after Leca andDormieux, 1990)

(b) Failure mechanism MII

Ω

σT

σS

H C

D

Ω

γ , c', φ'

αV

f'

Δ

(a) Failure mechanism MI

σT

σS

H C

D

Ω1 , c', φ'

α

V1

φ'

Δ1

Ω2

V2 φ'

Δ2

Δ(π)

Σ12 1

2

Δ(π')

σT

σS

H C

D

γ , c', φ'

α

V

φ'

Δ

(c) Failure mechanism MIII

c' = cohesionφ' = friction angle



55

Both MI and MII are characterized by only one parameter, the angle α between theaxis of the cone adjacent to the tunnel and the horizontal. MIII is also characterized byα; the geometry is similar to that of MI except that the cone is inverted and the

discontinuity velocity V along the failure surface reversed.The problem is analyzed in terms of five dimensionless parameters: C/D, σS/σC, σT/σC,γ D/σC and Rankine earth pressure coefficient for passive failure K P (or K A for activefailure). An upper bound solution is then found, given that in order for the set of external loads {σS/σC, σT/σC, γ D/σC} to be stable, the power ℘e of the loads applied tothe system and the power PV that can be dissipated inside the system during itsmovement must satisfy

e V P ℘ ≤

or in the form

S S T N Q N Q Qγ γ + ≤

for collapse mechanisms MI and MII and

S S T N Q N Q Qγ γ + ≥

for blow-out mechanism MIII, where the parameters associated with mechanism MIare given below as an example.

NS and Nγ are weighting coefficients that depend on the angle α, as in the followingrelations:

( ) ( )

2

'

1

cos 2 cos 2 D

S

E

R N tg

Rα

φ α =

−

3

3

11

3 D

B

E

R N R tg

Rγ α

⎡ ⎤= −⎢ ⎥

⎣ ⎦

QS, QS and Qγ are three loading parameters as in the following relations:

( )1 1S S P

C

Q K σ

σ = − +

( )1 1T T P

C

Q K σ

σ = − +

( )1 P

C

DQ K γ

γ

σ = −

R B, R D, and R E are parameters for the simplification of expressions (i.e. "convenientcoefficients"):



56

( ) ( )''

'

cos cos

sin2 B R

α α φ φ

φ

− +=

'2sin 2 sin 2

D

H R

Dα φ = −

( ) ( )' 'sin 2 sin 2 E

R α φ α φ = − +

K A and K P are Rankine earth pressure coefficients for active failure and for passivefailure, respectively:

'

'

1 sin

1 sin A K

φ

φ

−=

+

'

'

1 sin

1 sin P

K φ

φ

+=

−

The amount of material involved in the three above failure mechanisms is limited, butsuch geometries could be representative of initial ground movements that could lead tolarger scale failures. These solutions can provide reasonable estimates of critical face

pressures.

b) Analysis method of limit equilibrium by Kovári and Anagnostou (1996)

The stability of the face involves the assumption of a simplified failure mechanism in

the ground ahead of the face. The three-dimensional model of Horn (1961) shown inFigure 37 is close to reality and is simple to handle, which will be used for both slurryand EPB modes of operation. It consists of a wedge in front of the face and a prismextending up to the surface in the state of limit equilibrium. The support force S as afunction of the inclination of slip surface ω is also shown on the right side of Figure37. Geometrical parameters and notations of the computational model for face stabilitydesign are given in Figure 38.



57

Figure 37: Failure mechanism consisting of a wedge and a prismatic body (after Horn,1961, adopted by Kovári and Anagnostou, 1996)

Figure 38: Computational model for face stability design - Geometrical parameters

i) For slurry-shield-driven tunnels, Mohr-Coulomb failure condition and drainedconditions is assumed. Complex interrelations between the various parameters (shear strength and ground permeability, suspension parameters, slurry pressure, geometricdata of the tunnel, and safety factor) are given below.

inclination of the slip surface

s u p p o r t f o r c e

S

ω ωcritical

Smax



58

Considering the failure mechanism, at each point on the slip surface, the mobilizedshearing resistance τ is given by

tanc

F F

φ τ σ = +

where σ and F denote the normal stress and the safety factor, respectively.

The mean effective vertical stress σv along the interface plane between the prismatic body and the wedge (i.e. the silo pressure at the tunnel crown elevation) is given by

( ) ( )'

tan / tan / tan /1tan tan

w w H r H r H r t v

r cr ce e e

λ φ λ φ λ φ γ γ σ

λ φ λ φ

− − −−−= − + −

where parameter ( )0.5 tan / 1 tanr D ω ω = + is the ratio of the volume to the

circumference of the prism.

In view of the stabilizing effect of a bentonite slurry, to prevent a seepage flowtowards the excavation face, the pressure p b in the slurry must exceed the pore water

pressure pw in the soil. The effectiveness of slurry support depends on the infiltrationdistance of the suspension into the ground e. The suspension will come to a standstillafter the penetration reaches a distance emax, owing to its yield strength.

max

0

11

1 b w

w s

e

n ve

f k

μ γ

μ

= ≤

+

10max

0 2 s f

p d pe f τ

ΔΔ= = (DIN 4126)

where,

n = soil porosity;

μ b = dynamic viscosity of slurry;

μw = dynamic viscosity of water;

v = excavation rate;

k = soil permeability with respect to water;

Δ p = p b - pw is the excess fluid pressure, a main feature of slurry shield tunnelling; itcan be varied by adjusting the air-cushion pressure in a hydro-shield;

f s0 is the stagnation pressure gradient which is an experimentally measurable constant;

0

10

2 s

f d

τ = , with τf is the yield strength of the slurry, and d10 is the effective grain size

(characteristic grain diameter) of the soil.

The membrane-model can be assumed with the formation of an impervious membrane(a seal or a filter cake) on the face. In this case, face instabilities are hardly to occur when a slurry shield is used, even when the ground has extremely low shear strength.



59

But when the slurry penetrates into the ground, the validity extent of the membrane-model will be questioned.

With slurry penetration into the ground, face stability assessment will be different. Thesupport force S can be derived by following simple expression:

0

12 tan

S e

S D ω = − if e < Dtanω

0

tan

2

S D

S e

ω = if e > Dtanω

where S0 denotes the support force of the membrane-model (i.e., at e = 0).

The stabilizing effect of the slurry is attributed to the mass forces associated with the pressure gradient inside the suspension saturated ground. Relationship between the pressure gradient f s and the stagnation gradient f s0 is given by

0b

s s w

w

v f f n

k

μ γ

μ = +

The lower the pressure gradient, the lower the safety factor, and face instability occurswhen the pressure gradient is lower than a critical value f cr .

But of interest is that a slurry shield machine can cause significant ground heave(upward movements), e.g. during the construction of tunnels through very soft siltyclay and peat, if the pressure gradient is excessive.

ii) For EPBM, at limit equilibrium, the necessary effective support pressure s'(acting on the tunnel face) is a function of the tunnel diameter D, the overburden H, the

piezometric head in the chamber hF, the elevation of water table h0, the shear strength parameters c and φ, the submerged unit weight of soil γ ' and dry unit weight γ t,included the effect of seepage flow:

( )' '0, , , , , , , , , F t wedge prism

s f D H h h c φ γ γ λ λ =

with λ prism = ratio of horizontal stress σh to vertical stress σv within the prismatic body

and λ wedge = ratio of horizontal to vertical stresses within the wedge

The effective stabilizing pressure in the working chamber (s') is in the general form of the limit equilibrium condition:

' ' '0 1 2 3

h s F D F c F h F c

Dγ γ

Δ= − + Δ −

0' ' '

0 1 2 0 3

2

2

Dh

D s F D F c F h F c

D

γ γ

⎛ ⎞−⎜ ⎟

⎛ ⎞ ⎝ ⎠= − + − −⎜ ⎟

⎝ ⎠



60

The theoretical minimum face support pressure for tunnelling in dry soil is given bythe following equation:

0 1t s F D F cγ = −

where F0, F1, F2, F3 = dimensionless factors from nomograms, as function of H/D andφ'; h0 is water level, hF is the piezometric head in the chamber, Δh = h0 - hF is headdifference between chamber and ground, and it should be kept as low as possible. If the material in the working chamber is in a fluid state, s' = 0 and solving the equationfor Δh the necessary water pressure for equilibrium is derived.

The stability of the tunnel face is guaranteed through the joint effects of the effectivestress s' and the pore water pressure p in the working chamber. Stabilization measureswill depend on the interplay/compromise of the tunnel geometry, ground improvement,and support of face.

3.4.1.3 Countermeasures to Ground Failure

Ground settlement has the potential to damage overlying buildings and other installations/infrastructure including utilities. This can range from small internal cracksin plaster to effects on the structural integrity of the building (e.g. due to excessivedifferential settlement/angular distortion), although in most cases there is nodiscernible effect on the structure itself. The application of the appropriate measures tocontrol and mitigate against the effects of settlement can reduce this impact toacceptable levels.

Constructional measures to reduce the risk of ground failure include:• Prevention of unbalanced pressure at the face.

• Ground improvement: Consists of grout injections; jet grouting; and freezing.Grouting operations aim at increasing the strength and stiffness and/or reducingthe permeability of the ground.

• Prepared stations for TBM: These are predetermined stopping locations for EPBor slurry TBM for maintenance purposes in densely urbanized areas on a longstretch and under difficult geotechnical conditions.

• Grouting for block (boulder) stabilization: To treat loosened blocks between thecutterhead and the face, which may damage the tools on the head and cause over-excavation leading to local instabilities.

• Real underground structures: Such as forepoling, jet grouting arch, pipesumbrella (pipe jacking of a series of tubes filled up by concrete), or evenheavier/more complicated structures to allow an adequate reduction of risk.

In the following only one ground reinforcement technique will be discussed, that is theexecution of grouted bodies.



61

3.4.1.4 Grouted Bodies

Generally, TBM drives should avoid the involvement of extra work (groundimprovement) as much as possible. But in specific cases, grouted body may form anintegral part of EPB and slurry shield drives.

Figure 39 shows six possible cases of executing grouted bodies. Case 1 has only amodest grouting in the roof area, since the ground has a sufficient average cohesion butlocally mixed with materials possessing no cohesion. This unsystematic consolidated

body needs not statical calculation.

Cases 2 to 5 indicate the grouted bodies with a well defined shape and size and clearlydefined shear strength parameters. The most important and most frequently applied

body is presented by case 2 and 3. Case 2 is considered preferable by Kovári, however,Kochen (1992) deemed that geometry in Case 3 is better. Grouted bodies according tothe cases 4 and 5 are extremely work intensive and costly. The case 6 shows the

prepared stations for the preplanned maintenance work in the TBM's workingchamber.

Figure 39: General layout of grouted bodies (Kovári, 2004)

Systematic grouting operations can be executed from inside or outside the TBM asshown in Figure 40.



62

a) b)

c) d)

Figure 40: Injection schemes: a) From inside TBM; b) from the surface; c) from anauxiliary adit; d) from a vertical shaft (Kovári, 2004)

Grouted bodies have to achieve the minimum required strength and a satisfactoryhomogeneity. Figure 41 shows a simplified sketch of virtual arches within the groutedslab (according to Case 2 in Figure 39) used for design considerations. The assumptionhere is that, the grouted material is stressed to its limit state. The uniaxial strength of the grouted body will govern the state of stress in such virtual arches under a uniformlydistributed vertical load q.

In failure state (state of limit equilibrium), by assuming that the bending moments at

the supports and in the centre of the arch are zero, then there exists the followingsimple relation between the load, the uniaxial strength of the grouted body and thegeometrical parameters:

*

28 c

hd q

bσ =

where: q* = load in limit state

σc = uniaxial strength of grouted body

b, h, d = the width/span, height, and thickness of the virtual arch



63

Figure 41: Statical action of a grouted body above the tunnel, both in transverse andlongitudinal directions (Kovári, 2004)

In designing a grouted body, a good relationship between its geometry (shape and size)and its uniaxial strength σc (degree of homogeneity) should be achieved. For a givenload q and a factor of safety SF it can be beneficial to increase the size of the body infavour of a reduction of the requested uniaxial strength σc of the body.

The planning of the grid of drill holes and the grouting intervals along the individualdrill holes will depend on the shape and size of the grouted body as well as the type of grout and the amount per cubic meter of soil.

In practice, the face support pressure p is often considered together with the cohesion cof the untreated ground and the safety factor FS. The consolidated slab should be

properly designed with its thickness h and span ℓ . Thanks to the grouted slab in theroof area of the tunnel, the support pressure needed to stabilize the face willconsequently be smaller than the case having no grouted body. With the presence of the slab, the weight of the prismatic body in the failure mechanism has been isolated;therefore, support pressure is only required to sustain the wedge part (see Figure 42).



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Figure 42: Support pressure in cases of with and without grouted body

The practical meaning here is that, in the case of an EPB machine above the water table and a small value of ground cohesion and without important objects to be under-

passed, an open mode of operation can be envisaged.

In the case of collapse of the working face, the main purpose of grouted body is to

bridge over the resulting void thus avoiding a failure reaching up to the ground surface.But a through-going grouted body also reduces to some extent the risk of failure of theworking face.

In summary on the discussion about the grouted bodies, following major benefits can be pointed out:

- reduction of support pressure

- high safety against collapse

- reduced ground settlements

- safety during work in the chamber

ground surface

a) without grouted body

a) with grouted body shieldlining

W1

q

W2 p

shieldlining

annular grouting

H

D

D = 10 mH = 19 m

φ = 300

W2 pD

ℓ

hconsolidated slab



65

- control of time schedule

It should be recalled that, grouting operations for ground improvement in TBMtunnelling are uncommon and always expensive; therefore this kind of work should bespecified in the technical specifications.

3.4.2. Case History: Metro of Turin

GTT and Overview on the Project

GTT (Turin Transportation Group) is the company that manages the Torino publictransport network. GTT is the concessionary for design, construction and managementof the Metro Line 1. The construction of Torino Metro Line 1 is one of the maininfrastructures in the public transportation plan for the Torino area. The first section

from Collegno (depot) to Porta Nuova includes 9.5 km tunnel and 15 stations (Figure43).

Figure 43: Alignment of Torino Metro Line 1 (Crova R., 2006)

The civil works design was governed by the VAL (Automated Light Vehicle) systemcharacteristics shown in Figure 44. The train is 2.08 m wide, 52 m long; and itsmaximum passenger capacity is 440 people (6 pass./m2). Because the train width is2.08 m, then a single 6.8-metre diameter circular tunnel contains the double track linehas been chosen, which was bored by TBM. The tunnel Metro construction works has

been divided into Lot 3, Lot 4, and Lot 5. At the lowest point of the longitudinal profile, the tunnel runs at significant depths (approximately - 28 meters). Not tomention the advantages and/or constraints for these deep tunnels, their disadvantagesinclude deeper and more expensive stations, and excavation work below the water table.



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Figure 44: Rubber wheel trains of Turin Metro (Crova R., 2006)

3.4.2.1 Subsoil Conditions

The first section of Line 1 has been completely excavated in the upper part of thefluvial-glacial and fluvial deposits. These deposits present horizontal and verticaldiscontinuous levels (lens) with different grain size distribution and varying degrees of cementation. Figure 45 shows the grain size distribution obtained from macro-samples(0,5m3) from stations/ventilation shafts excavation.

“Geo” constraints in construction method choices were:

- soil: gravel with sand and a high percentage of hard rock blocks and pebbles,from low to very low percentage of silt and clay;

- presence of random layers (lens) of loose material (sand and/or gravel);

- random degree of cementation; - groundwater table



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Figure 45: Grain size distribution (Crova R., 2006)

The ground grain size distribution was abnormal and different from the designforecasts, due to the absence of fine materials (less than 2%), and the almostsystematic presence of cobbles and boulders in very high percentages. This extremeground grain distribution did not allow to efficiently operate the TBMs in EPB mode;

significant soil conditioning problems were encountered with segregations of the muck in the excavating chamber and consequent operational and face stability problems(Grandori et al, 2003).

3.4.2.2 Shield Machines

From those "geo" constraints, all the contractors chose EPB TBMs to carry outexcavation beneath the water table under the railway links, for the best rate of construction, and for lower costs compared to traditional methods. However,disadvantage here is that, this is the first use of TBMs in the very coarse Torino soil.

The TBMs used in Lots 3 and 4 are new models from LOVAT Inc., the third one usedin Lot 5 is a second hand one produced by NFM.



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The following table gives the main characteristics of the shield machines.

TBM model

Tecnical data

LOVAT RME

306 Series 20600

(Lots 3 and 4)

NFM TBM - EPB

Mod. 13310506/001

(Lot 5)

Excavation diameter 7,802 mm 8,030 mm

Cutter head power 2,100 kW 2,000 kW

Cutter head speed Variable: 1 - 2 rpm Variable: 0 - 2.4 rpm

Propulsion thrust 76,000 kN 91,350 kN

Torque 20,400 kNm 15,000 kNm

Shield length 10.0 m 9.1m

Back-up length 98 m 100 m

Figure 46: TBM LOVAT RME 306 Series 20600 used for Torino Metro Line 1



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3.4.2.3 Tunnel Lining and Excavation

The tunnels were lined with pre-cast 30 cm thick segments in reinforced concrete,connected by bolts and EPDM gaskets to insure water tight conditions. Even withrather small curves and consequent assembly offsets of the segment ring, there is no

water passage within the tunnel.Each 1.5 m long ring consists of 6 “normal” elements plus one “key” element thatenables the closure of the ring, a “universal” lock that permits to adapt the ring to anykind of radius, from the minimum to the linear one, by a simple rotation of every ringcompared to the previous one along the tunnel axis at a given angle (Figure 47).

The injection of mortar behind the segments, performed immediately at the beginningof the excavation procedures, ensures the reduction of superficial collapse and thecorrect confinement/bedding of the lining.

Figure 47: Tunnel lining configuration of Torino Metro Line 1

Tunnel excavation with TBM started in October 2003 from Fermi station (Lot 3). It

has been necessary to find a correct balance of consolidating agents within theexcavated materials in the excavation chamber, to make the excavated materialhomogeneous. Because the subsoil of Turin is extremely varied in terms of grain sizedistributions and mechanical behaviour, soil conditioning was done to

• better the support pressure at the excavation face;

• lubricate the muck material in order to facilitate its passage through the screwconveyor;

• reduce the engine power at the excavation shield;

• avoid TBM engine overburden



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A large quantity of conditioning agents (emulsions of water, air and foams withaddiction of polymers) has been used.

Lot 3 and Lot 4 run completely outside the water table and underneath the central aisleof Francia Street. A light consolidation treatment was carried out in the tunnel crown

area, in order to avoid a collapse of the excavation face. The EPBM was operated witha partially filled working chamber, even under low or very low pressure (partial closemode). The TBM of Lot 4 was operated with an empty excavation chamber (openmode). There were no problems with face stability, partly because of the favourablesoil condition, which is in average more cemented than the prevision.

Lot 5 was executed in more difficult conditions: below the water table; below the old buildings; with very small radius curve; and simultaneous horizontal and verticalcurves. Various consolidation techniques were planned for the protection of buildingfoundations and reducing or cancelling the influence of the excavation on the pre-existing structures, and to improve the soil mechanical characteristics where necessary.

The TBM performance with a negligible pressure applied at the face, with provision of a small slab of grouted soil at the crown, is characterized by an effective averageadvancement of 10 meters per day.

The first Metro section of Lot 4 had been completed in time for the Winter Olympicsheld in Torino in February 2006.

3.4.2.4 Ground Improvement

Soil improvement solutions have been implemented where the assessments indicate

potential risk of damage to the pre-existing structures. Such interventions includeimproving the properties of the ground and mitigating the deforming effects induced

by tunnelling by means of low-pressure cement injection grouting. A consolidated slabis created above the tunnel section in order to avoid any localized instability fromdeveloping around it.

Different grouting geometry have been defined, based on relative position between thetunnel and pre-existing structures, as well as site accessibility and surface site areasuse.

The project includes full-face cement grouting in the areas adjacent to the stations

where the TBM will enter into or exit from the stations: the diaphragm walls in these particular areas will be partially demolished to let the TBMs in and out. In accordancewith the environmental conditions, the drilling and grouting operations were done fromthe surface and/or from in service shafts and tunnels (Figure 48).



71

a) b)

c)

Figure 48: Some schemes of grouting works (Crova, 2006)

It was required that the EPB technique be used to its maximum capacity. In addition tothe injection of bentonite, a new plant was also set up for the preparation and injectionof heavier substances obtained by mixing calcareous filler mixtures with water, tointegrate the ground conditioning with foams by way of optimized FIR (foam injectionrate/ratio) and FER (foam expansion ratio). All the critical points and most of theobstacles were overcome successfully; the excavation was carried out always in closemode (pressure at the top of the tunnel around 20÷30 kPa).

A systematic consolidation of a slab over the tunnel section was decided to beassociated with EPB 02 operating mode (i.e., the pressure in the top of the excavationchamber was kept between 0.1 and 0.3 bar, the penetration rate up to 50 mm/rev, andthe quantity of conditioning agents FIR 30%). Professor Kovari as expert of theContractor then determined two type of slabs (Grandori et al, 2003) for Lot 3:



72

o Light slab: “non structural” (too lightly consolidated and too small to beable to form a structure that can be taken into account in a staticalcalculation) having just the function of increasing the ground cohesion inthe most critical crown area of the tunnel. The depth from the surface to thetunnel axis is approx. 16 m in average (Figure 49).

Figure 49: Light grouted slab on top of tunnel

o Structural slab: having sufficient dimension and subject to heavier consolidation in order to assure a structural behaviour to be taken intoaccount in the static verification of the tunnel stability (Figure 50).

Figure 50: Structural grouted slab on top of tunnel



73

The light slab associated to EPB 02 operating mode systematically all along the metrotunnel drive. The structural slab associated to the EPB 02 operating mode in the mostcritical area nearby important buildings and under important subsurface and surfaceservices.

The continuous control of the weight of the excavated muck furthermore allowed todetecting in real time few local small over-excavations that were immediately filled byadditional grouting.

For the purpose of completeness, we also like to mention the execution of specialgrouted soil structural bodies to protect the main buildings during the construction of Lot 5 of the Turin Metro Line 1 tunnel.

Grouting design had to be extremely accurate since it had to take into consideration

various aspects such as:o the presence of underground lines not to be hit by drillings works;

o the presence of buildings, structures, underground constructions that werelimiting the drilling possibility;

o to limit the disturbance caused by the drilling and grouting operations onsurface;

o the presence and level of the underground water table.

Four different shapes of injected body were finally designed as in Figure 51. The shape

(51.a) is the treatment scheme for the top part only for the passage of the TBM. Theshape (51.b) is the treatment scheme on the crown and at both sides up to thespringline for driving under street. The shape (51. c) is the grouting scheme on thecrown and at both sides below the springline for building areas. The shape (51.d) is thetreatment scheme completely around the tunnel for the maintenance of TBM. The firstthree schemes are the intervention of preventive consolidation by means of cementinjection. The last scheme shows preventive consolidation and waterproofing by meansof cement and silicate injection.

All these shapes were designed to form tridimensional structural bodies to avoid thatany over-excavation and/or instability occurred at tunnel level could be transmitted to

the surface buildings.



74

Figure 51: Different grouting bodies schemes at Lot 5 of Turin Metro Line 1 (Concilia,2005)

During grouting execution all injection parameters were recorded to increase theknowledge and behaviour of soil and to detect the local presence of fine lenses in caseof low absorption of injected fluids. Quality of injected mixture was controlled during

operations both in terms of density and of compressive strength, in order to comparewith the designed values (γ = 1.25 t/m3 and σf = 0.10 - 0.12 MPa).



75

Chapter 4

4. Interface Between TBM and Lining

4.1 Types of Linings

4.1.1 General

Lining is a structure to secure a tunnel space by withstanding the earth and water pressures. Lining consists of primary and secondary one. The lining is in general a ringstructure assembled with prefabricated segments, but is built in some cases with cast-in-place concrete. The secondary lining may be placed mainly with cast-in-place

concrete if required.Segment is lining material for the shield tunneling. In general, it is made of reinforcedconcrete or of steel. Several segments are assembled to form a circle, multi-circle or other shape.

Tunnel lining should be designed and constructed to high standards across the project.This will cover issues including, how intermediate construction stages need to be takeninto account, settlement mitigation measures and the impact of backfill grouting. Itshould satisfy the principles and requirements for safety, serviceability and durability.

The following types of lining need to be distinguished:

- pipe lining (pipe jacking)

- “in situ” lining

- segmental lining

With pipe jacking, behind the shield and guided by means of a pilot head, pre-fabricated pipes, which are pushed forward from a launch shaft, constitute the final

lining. With machine drives, excavation and installation of the pipe are not normallyconcurrently operations. The lining is constituted of individual pipes inserted in the



76

launch shaft, and the ever growing string of pipes is jacked forward by means of pushcylinders. Without a tailskin and an erector, the shield is very compact (Figure 52).

Figure 52: Pipe jacking diagram. Typical job sites (Herrenknecht)

“In situ” linings do not require pre-fabrication. They are cast right in the shield area.The most modern and promising variant is “extruded” concrete, where the concrete isapplied under pressure. Behind the shield the tunnel lining is concreted in rings behinda shuttering (the lining is slipcast behind a sliding form). To advance, the shield can

push against the hardened concrete section, which must have reached the requiredstrength (Figure 53).

Figure 53: Hydroshield with telescopic trailing shield for concrete extrusion, Métro deLyon, 1993 (Maidl et al, 1996)



77

TBM tunnels can also utilize sprayed concrete for initial (with steel fibres) and finallining (without reinforcement). Integrated concepts for TBM’s and mechanizedexcavation systems has been shown by Melbye (2005), where design and build are

based on modular concepts to meet most sprayed concrete requirements andspecifications in tunnelling and shaft sinking. The example of a TBM tunnel with a

full, circular sprayed concrete lining is given in Figure 54 & 55. In this case, the archeffect can be calculated and the bond strength is no longer a factor.

Figure 54: The example of a TBM tunnel with a full, circular sprayed concrete lining(Melbye, 2005)

Figure 55: Robot spraying manipulator is integrated into a large diameter TBM(Melbye, 2005)

With segmental lining, which is the focus of this report, rings made from a number of segments are installed within the protection of the shield tail. The lining segments are

pre-cast and transported to the place where they will be positioned.

Following are the segment and ring nomenclature (Figure 56 & 57).



78

Figure 56: Ring nomenclature

Figure 57: Segment nomenclature

Segments and rings can have various types: segments can take one of the rectangular,trapezoidal, or honeycomb forms (see Figure 58); rings can take one of the straight,right/left, or universal forms. Segments are connected together by some types of jointdesign (conservative with tongue and groove or advanced with plain surface) and jointconnector (bolt or dowel) (Figure 59).



79

Figure 58: Segment shapes

Figure 59: Circumferential and radial joint connectors. Plabutsch Double Lane Highway Tunnel in Austria (1998) (Wagner, 2006)

Activities that affect one single segment include pre-cast process, handling, storage,and assembling to constitute a ring. Activities that affect on the ring include TBMdrive / tunnel excavation, tail void injections, and “ground” loads.

Many kinds of materials are used to constitute the segmental lining: concrete, steel,steel fiber, connectors-bolts (plastic and/or steel made), gaskets for the waterproofing(elastomeric neoprene rubber and/or hydro swelling material). For compressiveEPDM-sealing gaskets, it is better to use a wide and flat than a narrow and highgasket.

In designing the segmental lining, one can use different Norms and Standards, such asEuropean standards or local standards of the specific country (ACI - AmericanConcrete Institute, DIN - German Institute for Standardization, BS - British Standards,SNiP - Russian Construction Norms and Regulations, etc.). Generally, just a right tune

of the various coefficients is adequate to meet all the requirements in differentlocations, since the basic materials are well known (concrete and steel). However,



80

specific attention must be paid to the new generation of the “well known” materials,i.e. high performance concrete, and steel fiber reinforced concrete.

4.1.2 Reinforced Concrete Linings

Reinforced concrete segments are by far the most commonly used. The segmentalreinforced concrete lining is used to satisfy many construction and/or environmentalrequirements, for instance:

¾ the need for an immediate support (mainly for an excavation in an instableground);

¾ the need to control carefully the ground movements induced by the tunnelexcavation;

¾ to avoid the drainage of the groundwater and therefore to build a waterproof tunnel;

¾ provide the counterbalance for the TBM advance;

¾ to avoid the installation of a secondary lining.

With respect to a segmental lining installed in the rear of a single or double shieldedTBM with or without the face pressure control (Figure 60), the essential issues are to

make choice of it, to pre-dimension it, and to perform the static verifications for it.The basic elements that must be known include: a) the geometry (general and detailed)of the chosen segmental lining; b) the actions undertaken by the single segment and bythe full ring all along their life; c) the characteristics of the materials constituting thevarious parts; and d) the norms and standards to be applied.

Figure 60: Area near to the face where tunnelling operations with the use of a TBMoccur



81

Geometry and relevant tolerances of a lining segment are given in the following Table6 and Figure 61.

Table 6: The segment tolerances - limit deviation

Description Tolerances

Width: ±1.0mm

Thickness: -0/+3.0mm

Length of an arc of circumferences: ±1.0mm

Radius of intrados: ±2.0mm

Diagonal of the segment: ±1.0mm

Position of the holes for the connections: ±0.5mm

Position of the hole for the erector: ±2.0mm

Depth of the groove for the gasket: -0.5+0.1mm

Planarity of the faces which meet other elements:

±1.0mm

Figure 61: Geometry and relevant tolerances of a lining segment

Nevertheless, the most important principle must be to keep the assembly tolerances asgenerous as possible so that they can be maintained on site, bringing about the ringerection personnel's work as easy as possible.



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4.1.3 Steel Fiber Reinforced Linings

Using Steel Fiber Reinforced Concrete (SFRC) for precast tunnel segments has severaladvantages, because of the following (Plizzari & Tiberti, 2006):

¾ SFRC is a tough material

¾ Smaller crack width (durability)

¾ High resistance to impact loading (as it may occur during transportation or the segment placement)

¾ Better control of possible detachments of concrete cover

¾ Industrialization of the production process

¾ Smaller area for stockpiling conventional reinforcement (rebars or wire

mesh)

¾ Steel fiber reinforcement is present in the cover, narrow corners or holeswhere conventional reinforcement can hardly be placed

However, attention needs still be given to the SFR lining subject to loading conditions.Loading conditions range from the transient phases to the serviceability phase.Transient phases include storage, transportation and placement of segments, and thrust

phase. Under serviceability phase (i.e. during the expected life of the tunnel), the liningsustains ground and water action. During pushing of the hydraulic jacks, an optimizedreinforcement should include rebars (for localized stresses under the jack) and fibers

(for diffused stresses in the segment), so that bending cracks and concrete spalling willnot occur. Because of the FRC toughness, the load increment on the segment could beachieved; in other words, the FRC toughness allows for an increase of the segment

bearing capacity.

4.2 Lining Design Procedure

There exist various competent methods of designing shield tunnel linings, and thisreport does not give priority to any one method. Today, the design and dimensioningof a reinforced concrete segmental ring are still carried out under consideration of itsultimate state. Limit states analysis allows checking of both the structure's factor of safety with respect to failure and its satisfactory behaviour with respect toserviceability. The main characteristics of the two limit states are recalled in thefollowing table.



83

Ultimate limit states Serviceability limit states

Failure of a section due to crushing of concrete

Excessive deformation of steel

Instability of shape (buckling, bulging)

Loss of static equilibrium at ring erection

Excessive opening of cracks(infiltration, corrosion)

Excessive compression of concretecausing microcracking

Excessive ring deformation

However, this subsection only introduce a few basic concepts of TBM lining design, soas to help understand better the TBM/lining interface which will be presented later.

4.2.1 Design Steps

Generally, design steps for TBM tunnels could be as follows (ITA, 2000):

Step 1: Define geometric parameters

Alignment, excavation diameter, lining diameter, lining thickness, width of ring, segment system, joint connections

Step 2: Determine geotechnical data

Shear strength of soil, deformation modulus, earth pressure coefficient

Step 3: Select critical sections

Influence of overburden, surcharge, groundwater, adjacent structures

Step 4: Determine mechanical data of TBM

Confinement pressure, overcut, shield tail conicality, TBM length, total thrust pressure, number of thrusts, number of pads, pad dimensions, grouting pressure,space for installation. All these structural parameters associated with TBMcharacteristics may have potential impact on ring stress analysis.

Step 5: Define material propertiesConcrete: compressive strength, modulus of elasticity

Reinforcement: type, tensile strength

Gasket: type, dimensions, allowable gap, elastic capacity

Step 6: Design loads

Soil pressure, water pressure, construction loads etc.

Step 7: Design models

Empirical model, analytical model, numerical modelStep 8: Computational results



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Response: axial force, moment, shear

Deformation: deflection

Detailing: reinforcement, joints, groove

The design of a shield tunnel lining often follows the planning works, according to asequence as shown in Figure 62.

Figure 62: Flow chart of shield tunnel lining design (ITA, 2000)

Function/Capacity to be given to Tunnel

Execution of Construction Works

Planning of Tunnel Project

AlignmentPlan/Profile

Cross Section

Load Condition

Model to Compute Member Forces

Survey/Geology

Specification/Code/Standard to be used

Assumption of Lining Condition(Thickness, etc.)

Inner Diameter

Computation of Member Forces

Safety Checking for Lining

Safe and Economical

Approval

YES

YES

NO

NO



85

4.2.2 Loading Conditions

The tunnel lining behind the TBM must be capable of withstanding all loads/actionsand combined actions without deforming, especially during ring erection and advance.Single-shell reinforced concrete segmental rings behind the TBM, can be designed to

fulfill those demands. Secondary lining can also be constructed with cast-in-placeconcrete as a structural member of the segmental lining.

There are many loading cases for the segmental lining of tunnels driven by TBMs.This part provides information on some actions that should normally be considered inthe design and construction of tunnel lining.

The following loads shall normally be considered in designing the lining of the shieldtunnel (JSCE, 1996):

(1) Vertical and horizontal earth pressure(2) Water pressure

(3) Dead weight(4) Effects of surcharge(5) Soil reaction(6) Internal loads(7) Construction loads(8) Effects of earthquakes(9) Effects of two or more shield tunnels construction(10) Effects of working in the vicinity(11) Effects of ground subsidence(12) Others

Various combinations of the loads can be considered according to the purpose of thetunnel usage. Table 7 gives a classification of these loads from the design point of view.

Table 7: Classification of the loads for shield tunnelling

Primary loads 1. Vertical and horizontal loads2. Water pressure3. Dead weight4. Effects of surcharge5. Soil reaction

Secondary loads 6. Internal loads7. Construction loads8. Effects of earthquakes

Special loads 9. Effects of two or more shield tunnelsconstruction

10. Effects of working in the vicinity11. Effects of ground subsidence12. Others



86

Figure 63 below shows the excavation process of TBM in order to analyze thenecessary loading cases. Cross section 0 is far away from the face, the initial state of stress in ground is not affected. Cross-section 1 is right at the face, where TBM cuttingwheel is in interaction with the ground. Cross section 2 shows the loading conditiondue to convergence of the ground on the TBM shield. In the cross section 3, lining is

subjected to the grouting loading Pg. Cross section 4 is within the part of hardenedgrout, the lining is subjected to permanent equilibrium loading Peq.

Figure 63: Excavation process of TBM

Concerning the segment loading, the steps which involve a specific verification for thesingle segment are: handling in the TBM; assembling to built-up the ring; thrust for theadvance; longitudinal injections (primary grouting); and radial injection (secondarygrouting) - but normally no more used nowadays.

Figure 64 gives the notations in the usual calculation method and the modified usualcalculation method (Effective stress method).



87

Figure 64: Notations in the usual calculation method and the modified usualcalculation method (JSCE, 1996)

The notations used for the structural calculation of lining are defined as follows:Bending moment (N), axial force (N) and shear force (Q) (for member forces, thedirections indicated in Fig. 65 are assumed to be positive).

Figure 65: Notations of bending moment, axial force and shear force

The temporary loads during segment transport, ring assembly and TBM advance withgrouting pressure in many cases are more important than the final loads from earth andwater pressure. Therefore, the following different groups of loadings may have to be

carefully considered.



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4.2.2.1 Geostatical Loads

This load case analyses the load effects on lining segments and ground. An example isshown in Figure 66.

Figure 66: Example load cases

Dead weight is a load in the vertical direction, distributed along the centroid of lining,and is included in this geostatical load case.

Dead weight of the primary lining shall be calculated by the following equation.

11

2 .c

W g Rπ

=

where,

g1 = Dead weight in unit length of the primary lining exerting along the centroid of lining (per unit length in longitudinal direction);

W1 = Dead weight of the primary lining (per unit length in longitudinal direction);

R c = Radius of centroid of the primary lining.



89

The water load is set according to the associated water levels with consideration of adensity of γw = 10 kN/m3. If the problems of geotechnical engineering (stability andsettlements) are combined with groundwater/pore pressure considerations, it would berather difficult to deal with, as it increases the complexity considerably.

4.2.2.2 Thrust Jacking Loading

The functions of the linings during tunnel construction are to sustain jack thrust for advancing a shield machine and to withstand the back-fill grouting pressure. Thelinings have also the function as a tunnel lining structure immediately after the shieldis advanced.

Thrust force of shield jacks (Figure 67) is a temporary load which acts on the segmentas a reaction force against it while advancement the shield machine and is the mostinfluential load to the segment among the construction loads. Several verifications

must be done for the jacking load effects on the segment, such as contact pressure, bursting forces in the radial direction, and bursting forces in the circumferentialdirection.

Figure 67: Thruster pads distribution and spalling and cracking of concrete cover

Segments can be analyzed using FEM-method principles organized, for example, inthe Structural Analysis Program SAP2000 (Computers and Structures, Inc. - CSI,2004) to investigate the behaviour of the lining following linear elastic Hooke law.Modelling can be done with barrel shell elements. Boundary conditions of model arerestrained on side of segment where it has contact with already installed ring. Loadsfrom thrust jacking shoes are distributed over the length of thrust shoe (Figure 68).



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Figure 68: Shell element generation (SAP2000 package)

With regard to the BEG tunnel, thrust jacking forces could be redistributed to thelining over thrust shoes contact area. Different extents of assumed forces are presentedin Appendix 3. Two maximal pressures (10,345 tons and 9,052 tons) would be used as

basis for loading analysis and further on for dimensioning of segments.

Thrust jacking loads are the design criteria to define necessary reinforcement for thelining.

4.2.2.3 Trailer Loading

Trailer chassis and other service loads can be applied on lining, including main bearingloads, divided by number of wheels (Figure 69). The loads induced by the trailer and

by any fixations in the segments normally do not influence the reinforcement. Duringdiscussions with TBM manufacturer, it is necessary to state whether "Main BearingLoad" will be included in this type of analysis or not.

Figure 69: Trailer load distribution

Considering the BEG Lot H3-4, for instance, if after excavation of the tube the TBMwill be dismantled and transported back through tunnel, then "Main Bearing Load"



91

could be assumed e.g. as approx. 165 tons. Also, additional assumptions may have to be defined as follows:

a) "Main Bearing" forces are acting on same distance as trailer load wheels (3500 mm)

b) 165 tons will be divided over 4 wheels (41.1 tons / wheel); additionally a horizontal

load which is on the safe side is set of 15%.

c) Not more than 1 wheel is acting on ring width (2.0 m), that means along the tunnelwagon wheels are on distance that is more than 2.0 m.

As a result, "Trailer Wheel Loads" might be taken as unfavourable one and as criteriafor definition of reinforcement (41 tons/wheel/ring width) regarding service loadconditions.

4.2.2.4 Grouting Loads

Primary grouting pressure applied to fill up the tail void behind the TBM is believed togovern both deformations and internal lining forces, as well as affect surfacesettlements. The grouting pressure acting on the outer surface (extrados) when the ringleaves the shield. For normal conditions, when a highly flowable mortar is used, thegrouting pressure can be calculated constant around the ring. The annular grouting of the ring, with a grouting pressure minimum one bar (1 bar) higher than the surroundingwater pressure, prestresses the ring and the enclosing ground.

Secondary grouting pressure is an extending regular grout pressure. These transient-type loads result from a localized increase in grouting pressure ("local pumping

thrust") directly behind the segment grouting holes (Figure 70).

Figure 70: Secondary grouting pressure



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As an example, the influence of gap grouting can be analyzed with accidental extent of grouting pressure of 4 bars (400 kN/m2 or 0.4 MPa).

In cross-section load will be distributed in the form of triangular plane, acting in therange of 0 - 400 kN/m wide strip of ring. Value of loading is changing linearly from

zero (0) to maximal pressure and back to zero (0) bar in range of middle angle of 45degrees.

In longitudinal section the extent of loading is continuous and has extent of 4 bars, or is acting also as a type of triangular loading (used in two-, three-dimensional model).

Influences from the geostatical and backfill grouting load cases need to be combined togive adverse resultant moment and shear forces.

4.2.2.5 Storage Loads

After mould stripping, segments are set down and stacked on supports. Timber blocksare usually placed between segments taking care that they are aligned with the supports(Figure 71). Storage and handling (e.g. turning, packing and then loading-outoperations, supply to the workface…) influence the bending moment.

Figure 71: Loads for storage of segments

As an example, two situations could be considered for the segments self weight on

stock of the BEG Lot H3-4 tunnel:

a) Storage of segments as simple beam: moment is calculated by

Ma = 0.125 x γ x b x d x l2 = 0.125 x 25 x 1.00 x 0.50 x 3.52 = 19.14 kNm/m width

b) Erection of segment - middle support: moment is calculated by

M b = 0.5 x γ x b x d x l2 = 0.5 x 25 x 1.00 x 0.50 x 2.72 = 45.56 kNm/m width

Because M b > Ma, therefore M b will be taken into account as maximal influence during

this loading case.



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4.2.2.6 Erection Loads

During erection, the lining is subjected to a number of loads such as: compressive(possibly eccentric) loads from the longitudinal thrust of the TBM; shear forces due to

differential deformations between adjacent rings; forces resulting from segmentsoverhanging during ring assembly; possible bumping impact loads; loads applied bythe assembly systems retained (bolts, anchor bolts or plugs).

i) Eccentric Loads during Shield Drive

+ Geometric Eccentricity of Thrust Shoe Action

For BEG project tunnel, loadings equal to maximal possible thrust jacking pressureover ring circumference of 10345 tons may have to be applied on segments. Thrust

pressures are defined in same way as for case of thrust jacking loads. Eccentricity

varies between 0 / + 5 cm toward tunnel center and 0 / -2 cm outward tunnel center andapplied on segment edge as distributed moment over thrust pressure length.

+ Variable Thrust Jacking Pressure

The same loadings as for the case of regular Thrust Jacking Loads are to be applied onthe segment edge but the level of forces as well as the location of application is varied(see Fig. "Eccentric Loads during Shield Drive").

ii) Eccentric Loads During Installation

Loading of 15 tons per only one thrust shoe can be applied on the segment edge. Thisload is equal to force necessary to properly install segment with plastic dowels (plasticdowel insertion force).

4.2.2.7 Fire Loads

Additionally, when fireproof concrete is used, an important aspect for the construction phase is that each segmental ring must be provided with adequate fire protectionimmediately following assembly. According to Haack (2003), the considerable effectsof the machine fire during the construction of the rail tunnel below the Great Belt inDenmark would not have occurred, namely causing splintering up to 27 cm deep given

40 cm thick segments, if such resistant segment concrete had existed at the time.However, loading of tunnel fire in construction is not further considered in this report.

4.2.2.8 Other Loads

Evaluation of the surrounding ground dynamic characteristics may be necessary inhigh seismic risk areas.

Temperature influence in the final state is avoided by the shielding effect of the fire protection lining layer. However, in the case of certain structures (very deep tunnels,

energy conveyance tunnels, etc.), climatic temperature-induced actions (such asuniform temperature variations and temperature gradients) must be considered.



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Concrete shrinkage is neglected. Other unusual load cases/accidental actions such asimpact by railway vehicles, explosions, fire loads, disaster load case of flooding insidethe tunnel, buoyancy or "waterhammer" etc. will also not be dealt with further.

4.3 Concept of Interface

In a specific tunnelling project, the main Client requirements are related to asset performance, asset management, capital delivery (cost & time), and environmentallysustainable. To fulfill these requirements, a strategy (to set up a proper organization) isneeded, that is to clearly identify the disciplines to be dealt with, the specific studies to

be developed, the interfaces, the sources of risk. By and large, the project interfaces

can be shown as in Figure 63, which are characterized by the coordination of technicaland functional design, aiming at minimum cost and reliable time schedule.

Figure 72: Identification of project interfaces (after Grasso, 2006)

More specifically, the TBM/lining interface implies both contractual and physicalmeanings and these two fields have certain extent of overlapping. The same is the strictlinking between the tunnel design and the tunnel construction. This reflects thestatement by ITA (2003): “Even the best TMBs cannot function efficiently if they arenot properly guided and the tunnel is not properly designed and managed”.

Project Interfaces

Equipment

Environment

Safetyand

Ventilation

Civil Works

Geologyand

Hydrogeology

Exploitationand

Maintenance



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4.3.1 Contractual Interface

Within the contractual discussions we can talk about several aspects. Those are theinteracting activities between the Parties to improve the execution of a TBM tunnel

project in general, to optimize the segmental lining, and to improve the interface between TBM and lining in particular.

4.3.1.1 General Aspects

Success for mechanised excavation depends upon correct planning and accurateactivities monitoring. Following main issues should be regarded in consideration of thegeneral essential interfaces (Grasso, 2006):

◊ the support of a strong political will;

◊ the public understanding;

◊ the financial pressures;

◊ the design of construction of logistics;

◊ the contract management;

◊ the risk sharing and management;

◊ the durability and serviceability;

◊ the technical feasibility◊ the constructability

By way of illustration, tunnelling in urban environment could be mentioned, whichinvolves the following key elements (Chiriotti, 2006):

- adequate excavation method

- consciousness of risks (all the Parties)

- strategy for mitigating risks- competent personnel (all the Parties)

- organization & responsibilities (all the Parties)

- development and implementation of ad hoc procedures

- identification of key indicators and implementation of consistent controls(monitoring)

As we can see from the above list, there are three fields that represent a closeinteraction between all the Parties involved to enhance the general quality of the

project (i.e. consciousness of risks, competent personnel, and organization &responsibilities).



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Regarding the consciousness of risks, a common understanding will help to reduce thesources of initial risks in urban tunnelling, including:

- geological risk

- design risk

- construction risk

- financial risk, and

- operation risk.

Going further into some details of consciousness risks, design risk can be due to:

lack of experience of the Designer,

uncompleted prediction of risk scenarios

insufficient definition of countermeasures non-constructability of proposed solutions

design flexibility vs. actual ground conditions

loading conditions of the lining

definition of TBM’s operational parameters

inadequate monitoring controls

inadequate threshold limits

And construction risk can originate from:

learning curve (a period at the beginning of every job for the tunnelling crew todevelop into a team and learn the idiosyncrasies of the new job)

incompatibility of the machine with the ground

major mechanical failures

inadequate logistics

lack of Contractor’s experience

lack of personnel training

lack of TBM’s parameter controls

lack of TBM’s parameter review

insufficient probing ahead

inadequate procedures

The construction risk is illustrated by considering this case: When tunnelling withEPB-TBMs in a non-conventional medium (i.e., no uniform granulometry, no uniformdensity and no uniform groundwater head), the possible failure mechanisms may



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involve the global failure, local failure, piping, and progressive failure. Ground andsurface monitoring are effective provided that they are integrated by TBM andconstruction data to allow a proper interpretation. Collapses may happen if:

TBM data are just accessible to the Contractor

The Designer is just receiving the in-ground and surface monitoring results

No effective back-analysis is in place because of difficulties in accessing data

With regard to the lining of EPB-TBM tunnelling in such a non-conventional medium,one can see that, the lining should be quality controlled by a checklist of events asfollows:

- water leakage

- steps between segments- lips/offsets between rings

- cracking after installation

- installation of defective segments/rings

- connectors, and

- erector failure

Regarding another key element on organization and responsibilities, a standard TBM

lining implementation plan must be prepared which details how the design andconstruction of TBM lining is to be managed. This will be adopted by all TBM liningdesigners and contractors.

4.3.1.2 Segmental Lining Optimization

Segmental lining systems offer a number of opportunities for optimization in detailwithin any phase of design. Because of the huge number of segments to be producedand because of the multiplying effect of any measure carried out, any optimization

becomes rather effective. Within the tender phase the fundamental features of a lining

system are to be established. But within the detailed design phase for construction,when the excavation system together with the segment production and the site logisticsare established, a number of opportunities to optimize the segments in detail becomedue again (Walter et al 2005).

The segment geometry, the geometry of the lining ring, and the application of thereinforcement can be taken into the optimizing consideration. Furthermore, segmentscan also be modified considering an integrated invert track in the railway tunnels inorder to optimize the construction logistics. The fundamental basis to enable this

process is a proper contract which manifests the design key figures at the one hand butalso enables optimization in detail at the other hand. And a proper collaboration

between the client, the designer and the contractor to serve for the continuity of the project philosophy and to serve for the input of the construction method is as essential.



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During all steps of design, the dialogue and the contractual basis between the peopleand parties involved should only manifest the main basics in view of the final result,and leave open the opportunity to optimize the segments in terms of the best technical,

practical and economical results (see Table 8).

In the preliminary design phase, the main decisions are taken to establish thefundamental tunnel system design, concerning the following questions: Tunnel systemconsisting of two single or one double track? Rescue system consisting of cross

passages between two tubes or separate rescue tunnels? Lining system consisting of mono-shell or double shell, shell sealed or unsealed? Fire safety is secured byseparated or integrated fire protection? What kind of dewatering and ventilationsystem? Use of conventional tunnelling or TBM, or both? And, segments or not?

In the tender design phase, the one system which is actually tendered has to bedesigned further into detail. This design includes: specification of the external loadsand load combinations to be considered; dimensioning of a suitable segment system to

derive a typical section including all details concerning the intermediate and final load bearing system; definition of all salient lining features concerning the sealing system,dewatering, fire protection, niches, cross passage interfaces; bill of quantities (BOQ) asa basis for tendering.

Table 8: Options of segmental lining optimization in relation to the individual design phases (Walter et al 2005)

Design phases

Preliminary design Tender design Detailed design for construction

BasicsPurpose of tunnel,constructionmethod

Tunnel diameter,lining system,ground, relatedrequirements

Typical section, liningsystem, qualityrequirements, loads andload combination

Options for optimization

Tunnel diameter,lining system,

preliminary

dimensioning

Best practicesolutions, finaldimensioning

Segment geometry,installation relatedfeatures, reinforcementdesign, logistics related

features

In the phase of detailed design for construction, the contractor shall be allowed toconsider the following: i) Final segment geometry, including segment width (ringwidth) and segment length (ring intersection), taking into account all belongings of handling, manipulation and installation; ii) Logistics related features concerning the

backup- and transport system as well as the construction method and constructionsequence; iii) Reinforcement detailed design which must cover the loadings definedwithin the tender and the loadings related to production, transport, installation and

TBM drive, but still suit the best practice of reinforcement manufacturing and of reinforcement cage suitability.



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So, it is the contract that should manifest completely the client’s requirements butshould not restrict the contractor’s opportunity to fulfill such requirements in the mosteconomical way and in a way which is most suitable to the TBM and backup systemavailable.

Structural concept on segment/lining

Statically speaking, the shell segmental lining should be dimensioned to maintain for the required support during excavation and over the entire lifetime load bearing.Kinematically, it should be designed to cope with all handling loads during each stageof segments production, manipulation, storage, transport and installation. The staticallyconcept and dimensioning of the segment lining system involve the following tasks(generic segment design):

- ground characteristics;

- segment partition (ring division); segment weight; outer and inner convergence of the lining;

- joint connection (tongue and groove design, or advanced design of plain joint, connectors, gaskets);

- minimum segment thickness;

- segment manufacturing (finishing, chamfer in the corners, allowabletolerances on lining and on moulds, ensured by QA/QC measures - i.e.quality assurance and quality control, etc.);

- external loads and load combinations;- non-cracked segments during installation (‘uncracked’ concrete);

installation precision;

- thrust forces undertaking.

Looking at the relation of the lining and high flexible (universal) machines, it isworthwhile to refer to the universal tapered ring (unified ring, Figure 73). Each projectis specific, but as a general rule one can say that unified ring can be used on asystematic basis for every alignment/situation. The tapers of one ring compensate for

those of another ring, thereby cancelling out the overall tapering effect. In regard tokinematic control of the segments, unified ring makes it easier to install owing to itslongitudinal and ring joints. The ovalisation tolerances of 1/1000 ÷ 1/2000 can beensured.



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Figure 73: Unified ring types (Wagner, 2006)

The unified ring is usually associated with the single gasket system for waterproofing.Here single gasket system is preferable to the double system, since the later has strongcompression characteristics. For example, the double sealing gaskets used for the ElbeTunnel (Germany) did not show real advantages and the costs are very high.

Reinforcement design

The reinforcement design can be completely open for the contractor to be establishedwithin the detailed design phase. In view of the huge number of the segments (e.g.about several thousands of segment rings, and dozen thousands of pre-cast segmentsand steel cages), a significant potential to reach an optimum between minimum overallreinforcement weight, efficient reinforcement cage production, and sufficient overallreinforcement cage quality is really worth to be taken full advantage of. Three maincomponents of the cages need to be kept an eye on (not to mention the specific localreinforcement such as additional bars, stirrups, and helix elements):

- principal inner and outer field reinforcement;- tensile splitting reinforcement in the longitudinal joints;

- tensile splitting reinforcement in the radial joints.

Potential for geometry optimization

For tunnel construction, the effort of optimizations by designer and contractor in proper and innovative cooperation with the client is an open end matter. For thatreason, the optimization process has to be followed up in all design phases. Within a

specific railway tunnel project, for instance, apart from above improvements threeother considerations for geometry modification can be mentioned:



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- intersection of the segment ring (span width of the roof segment);

- thickness reduction of the invert segment; and

- integrated track in the invert segment.

As a final aim, optimization process must successfully realize the benefits in terms of the segments geometry, the segment and reinforcement production and the best sitelogistics.

Remarks

It is well recognized, that if the cost of construction and operation are increased andthe rate of return on investment is inevitably reduced, then the viability of thetunnelling project will be threatened.

Following statement by Wagner (2006) is quoted as concluding remarks for the saidcontractual interface:

“It has been proven that, the length of a tunnel driven by TBM normally should

exceed approx. 2,000 m for the sake of economy. The TBM designer and the segment designer should join their effort to fix the common concepts before the

start of design work. Both designers may need to show minimum 10 years of

relevant experience. The Client should specify generic design of TBM and lining;

and responsibilities should be specified at interface of TBM and lining”.

4.3.2 Physical Interface

4.3.2.1 General

TBM/ground interaction

Interaction between TBM and ground is first briefed, because the type of excavationmethod and support that is used dictates the behaviour of the ground. Upon excavationof the face, the need for self-bearing time and the stability of unsupported span ( free

span) are of our concerns. Concerning this, a general rule to remember is that, "thetunnel is built at the face". The concept of unsupported span and self-bearing time arevalid both for conventional and full face mechanized excavations.

In Figure 74, the free span coincides with the last stretch of the tunnel where the rock is being excavated and the supports cannot be installed yet (very variable length,depending on the TBM type: open, shielded, with or without face counter-pressure).The advance is performed in two steps:

- Active stroke of the cutting head for the excavation (and the spoilextraction) usually 1.4 ÷ 1.8 (2.0) m;

- Advance of the whole machine when the cutting head has been stopped.



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Figure 74: Free span in full face mechanized tunnelling (continuous rock excavationand spoil/muck extraction) (Pelizza, 2006)

Apart from the unsupported span, other concerns include the disturbance of the groundahead of the face due to the cutting wheel rotation, and the shear failure of the groundalong the TBM skin due to friction when the machine is advancing.

Lining/ground interaction

As it is well known, the lining of the TBM tunnel has a number of functions, which putvarying demands on the form and the material of the lining. The following tworequirements need to be fulfilled with very little deformation over the whole workinglife of the tunnel:

- securing the inside of the tunnel against the surrounding ground andwatertightness in either direction

- taking up permanent or mobile loads resulting from installation and traffic.

The main parameters influencing behaviour of the tunnel lining in contact with the

ground (soil-structure interaction) are:- lining/back grouting material and ground/back grouting material contact

conditions;

- environment: nearness of existing or planned structures underground or atthe surface; and superimposed loads.

Lining/TBM interaction

The segmental ring is erected in the shielded TBM and during the advance, the rams

act on the ring; therefore, the ring never can be seen independent from the TBM(Gruebl, 2006). The interaction between machine, thruster configuration and geometry



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of the segments will influence the kinematics of erector and segments. The design of the TBM and the segmental ring must be harmonized in terms of:

• Rams must act on prepared sections of the ring (in correspondence with thelongitudinal joints and in regions where special tensile splitting

reinforcement is placed). Rolling of the tunnel shield and the ring must betaken into account.

• The ram axis should be identical with the ring axis. The rams axis radius may be slightly smaller (<10% of the segment thickness) than the middle ringradius. This gives the tendency to close the ring during advance.

• The segmental rings must be able to follow the TBM. The ring taper should be designed according to the TBM curve drive capabilities and not onlyaccording to the designed tunnel axis.

• The tail gap should be more than 30 mm to avoid ring constrains in the

region of the tail sealing.

• No steel sheets or timbers should be inserted in the tail of the tunnel shield.The new ring should be erected “free” on the last erected ring

It is also necessary to list the following general factors which play an important rolefor a successful TBM advance:

¾ Correctly working TBM with all devices and aggregates

¾ Guidance system, showing the correct position in correspondence with thetheoretical alignment/the designed tunnel axis (DTA)

¾ Segmental ring, interacting with the TBM, the structural requirements andthe DTA

¾ Well organized infrastructure (supply and disposal)

¾ Tunnelling team, knowing and controlling the equipment

¾ Tunnel management and supervision, assisted by DAT (Decision Aids inTunnelling)

In the following paragraphs, detailed discussions will be given on: machine operation,

TBM guidance system, ring building, backfill grouting, back-up system, and lininginstrumentation. The purpose is to highlight the TBM/lining physical interface in every process/operation.

4.3.2.2 Machine Operation

As already mentioned, important devices of the TBM are:

• Excavation system and excavation tools

• Systems for face stabilization according to ground conditions

• Transport devices for excavated ground



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• Steering equipment (rams, articulation cylinders)

• Ring erector

• Grouting system

The experience and technical skills of tunnelling machine operators as well as theavailability and use of experienced foremen are important factors in the reduction of risks.

If the ground quality is insufficient, the subsoil must be grouted, vibrator compression,injections or freezing to adapt it to the characteristics of the selected TBM.

TBM mechanical excavation is rather continuous, generates less dust, noise or vibrations, and provides superior protection. The profile accuracy of the cavity crosssection is particularly high provided the TBM is driven within its operating tolerances.

Problems concerning advance control include:

• Inaccurate survey of the TBM before start of tunnelling

• Incorrect definition of tunnel axis in reference to rail axis (consider of cant)

• Mistake during input of DTA (designed tunnel axis); snaky advancing;

• Problems with control of direction (refraction at tunnel wall, laser near lining)

• Incorrect driving back to the DTA after a deviation

Problem concerning lining is related to a particular limit condition of boreability inhard rocks. It is because of the fact, that in order to overcome the boreability problem,there is a tendency to optimize the ratio between cutterhead revolution and the thrust(lower speed higher thrust), which can give better penetration and less cutter consumption (as a result of less vibration). However, higher thrust can adversely affectthe lining bearing capacity (Figure 75).

Figure 75: TBM's thrust system affecting segments



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Driving the bore through the critical curves may create detrimental contact between theshield tail and the newly-built segments. Problem concerning subsidence in verycritical areas, i.e. under sensitive buildings with low cover, may be mitigated by fillingthe conical void around the machine with bentonite slurry, which is continuouslyinjected through ports located along the shield. This provided additional help to further

reduce volume loss due to the TBMs’ passage.

Hopefully, it is expected that the modern-day control cabin full of machine data plusControlled Boring Process (CBP) could facilitate the operators' work and achieve ever

better performance. Such an advance is one of many efforts to comply with production- and automation/robotization-related demands imposed by the concept of precast concrete segments tunnel linings.

4.3.2.3 Guidance System

Guidance of full-face TBMs is vital. Guidance system is to help showing the correct position of TBM in correspondence with the designed tunnel axis. Here are some basicdefinitions of terms:

TBM survey: Measuring and calculation of the real TBM-position anddirection in relation to the designed tunnel axis. A coordinated site systemwith fixed survey points should be set up on the field. In practice, only a smalldirection fault in the starting pit can result in big error in the far end shaft

Steering: Corrections of the TBM-drive resulting from real deviation

Monitoring and control: Record of the TBM-drive history (graphic andnumeric) and calculation, storing and analysis of all TBM and ring data

Main components of TBM guidance system are shown in Figure 76 below.

Figure 76: Components of TBM guidance system (Gruebl, 2006)



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It is highly recommended (for the double shield TBM is indispensable) that TBMs areequipped with a guidance system that provides in real time information on the actualalignment to the TBM operator (Concilia, 2006).

Apart from calculating the exact position and tendency (rolling and inclination) of theTBM for proper monitoring of tunnel alignment, the guidance system also measuresthe segmental ring for correct assembly (Figure 77).

Figure 77: Guidance system - measuring of the segmental ring

For any kind of the guidance system, it is necessary to know how quickly (speed anddistance) the TBM can react to modifications to the trajectory it is on.

4.3.2.4 Lining Ring Building

To add to the previous subsection dealing with the segment optimization, hereinafter are given some additional points in view of lining's interaction with TBM, in terms of segment selection, erection and bolting.

The tunnel lining is discontinuous and its structural properties depend on those of thesegments and contact joints between lining parts. Segment structural propertiesinclude: sectional area, inertia; modulus of deformation; and Poisson's ratio.Intersegment contact joint structural properties include: sectional area, inertia; and ring

composition.



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The choice of the adequate segment width (measured in the direction of tunnel axis) of the segment/ring is influenced by different and sometimes opposite exigencies:

- time of excavation;

- weight of the single segment;

- risk of damaging the segments while handling;

- geometrical compatibility with the rear of the TBM while the ring is comingout in the condition of the minimum radius of curvature.

The average width is varying between 1.00 m and 1.25 m (even 2.0 m) for big rings(diameter > 10 m) and between 1.25 m and 1.60 m for smaller rings. Large precastconcrete segments may weigh from 1 ton up to 15-19 ton.

Segment height is the height of main girders of segments measuring in the direction of tunnel radius, for the flat type segment, it is also called "Segment thickness”.

Segment length is the arc length of segment measured in the transverse direction of tunnel axis. Distinction is made between the external arc length (A), the arc length at

bolt pitch circle (B), and the internal arc length (C). The geometry (length, width,shape, inner conicity, etc) of the segments is defined by the interface between the TBMtail configuration and ring parameters.

The choice of the number of segments per ring is dependent on the tunnel diameter (Figure 78), and is also influenced by almost the same factors listed for the length of the ring:

- time of excavation;

- weight of the single segment;

- risk of damaging the segments while handling;

- available space for handling in the back-up.

Figure 78: Choice of number of segments versus tunnel diameter (Pescara 2006)

Examples of lining in some actual projects are given in the Table 9 below.



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Waterproofing of the ring is assured by the following factors which must be consideredall with the same degree of importance:

- very good quality of the concrete (compressive strength f ck is generally greater than 40 MPa) and of the curing process;

- careful handling to avoid any damage or formation of “latent” cracks;

- choice and positioning of the gasket;

- careful assembling of the ring;

- filling of the tail void with proper material in due time, volume and pressure.

Table 9: Ring and segment geometry (Wagner, 2006)

Diameter[m]

Thickness [cm]

Width[m]

Ring

division

[-]

Form/shape [-]

Length[m]

Weight[ton]

Groene Hart

NL - Railway13.3 60 2 9+1

Rectangular + key

4.37 12

Plabutsch

A - Highway11.1 40 2 6+0

Trapezoidal/Rhomboidal

6.02 12

SOCATOP

F - Highway10.4 42 2 7+1

Rectangular + key

4.45 9.4

Seattle

USA - Subway 9.42 40 1.6 8+0Trapezoidal/Rhomboidal 3.86 6.2

Wanjiazhai

PRC - Water4.3 25 1.4 4+0 Hexagonal 3.57 3.1

With regard to the ring assembling, the following should be noted:

- The order of arrival of the segments near the erector must respect the order of handling for the assembling process.

- The dimensions of the segment and of the backup are inter-related with respectto the movements (rotation and translation) that the segment itself must

undertake.

- The segments can arrive to the erector both in the upper and in the lower part.

Ring erector may be of several types, such as vacuum-sucking erector, mobile erector (mechanical system) with remote control panel, etc. having many active movementsnecessary for ring assembly (Figure 79). It is recognized that TBM erector capabilitiesare closely related to the learning-curve phase as well as sensitivity and assembly

precision.



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Figure 79: Erector arm of TBM, 6 necessary active movements for ring assembly(Gruebl, 2006)

The quality of lining depends not only on the erection of regular segments but also onthe installation of the key block (K segment). With all the segments in the ring as awhole, deformations such as offset, ovalization can happen as in Figure 80. In soft soilconditions, lining failure can occur before or even after ring closure, including:

- shear failure

- compression failure

- combined bending and thrust

- punching failure

- watertightness of segments

For K segment, there are two types in terms of the direction of insertion. One is toinsert from the inside of tunnel, in which the longitudinal side faces of a K segment aretapered in the direction of funnel radius ("K segment inserted in radial direction"). Theother is to insert in the direction of tunnel axis, in which the longitudinal side faces of aK segment are tapered in the direction of tunnel axis ("K segment inserted inlongitudinal direction") (Figure 81).

• With trapezoidal tapered ring, key position selection in curved tunnels is of theessence;

• Keystone condition during the assembly: The k-segment is the last to beinserted and thus the precision of the movements must be higher.

The movement of the k-segment during the insertion and its geometrical characteristicsform the basis to define the length of the TBM’s thrust system.



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Figure 80: Schematic view of ring ovalisation (Wagner, 2006)

Figure 81: Insertion of the k-segment (Pescara, 2006)



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The following Table 10 quoted from AFTES recommendations (1997) considers anexample of building a lining ring comprising rectangular- (standard) and trapezoidal-shaped (key and counter) segments. It details:

- the successive segment erection stages;

- recommendations associated with the operating environment for eacherection stage;

- remarks of a general nature for each erection stage.

Finally, robotic control of tunnel lining installation is an actual need for mega tunnel projects, in view of lining quality and tunnel excavation progress rate. Computer controlled precast segments tunnel lining erection will harmonize segment geometry

and machine configuration, aiming at automation, high quality and economy. Figure82 shows the moduli of the operational program, using a recording, warn and alarmsystem for higher advance rates and lower running cost.

The trend toward fully automated installation of segmental lining associates withdowel connectors. Future development of TBMs for large tunnel diameters leadstoward new products particularly larger dowels for automation of segmental lining.

Figure 82: SW robotic control system for segment erection, basic structure (Schulter,1996)

SURVEYING

SENSOR DATA

DATABASE

LINING

DATABASE

TBM

PROCESS

CONTROL

TUNNEL/RING

DATA

MACHINEINSTRUCTIONS FOROPTIMIZED TUNNEL

OPERATION

"KNOWLEDGE" OFSYSTEM ABOUT

TUNNELLING/ TBMCENTRAL

PROCESSING

WARNING &ALARMS

RECORDING MONITORING

CALCULATED STATE

PRESENT STATE

NEXT STATE



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Table 10: Lining ring building stages (AFTES, 1997)

SCHEDULE OF

OPERATIONSRECOMMENDATIONS REMARKS

1) Supply of first segment toerector.

Supply possible from:

- upper level;- lower level.

2) First segment pick-up.

3) Retraction of thrustcylinders corresponding to

placement of first segment.

Pick-up possible using suction pads, grippers, bolts.

4) Positioning of firstsegment by rotating erector.

Detailed analysis of loads in each pick-upsystem position and of indirect loads onsegments.

Light ray guidance systems canfacilitate approach and final

positioning of segment.

5) Radial approach of firstsegment.

6) Final approach withrotational, longitudinal andtransverse balanceadjustment.

Control of approach speeds by selectionof proportioning hydraulic controls.

7) Holding of first segmenton ring.

Pads of other thrust cylinders remainunder pressure in contact with other segments to safely ensure:

- segments holding and assembly

- compression of waterproofing gaskets

and prevention of their decompression.-stability of the machine under theconfinement pressure.

TBM main cylinder thrust on theother segments must prevent anyforward displacement of themachine.

At this time, the segment is

simultaneously held by the erector and the thrust from the maincylinders.

8) Fixing of first segmentBy ring/ring (longitudinal),segment/segment (transverse)connection.

9) Installation and fixing of standard segments.

Same recommendation as for the firstsegment.

Provide alternate installation of segmentsin each ring to minimize tube roll effects.

Same remark as for the firstsegment.

10) Installation of counter segments.

Use of template to calibrate gap betweencounter segments.

Same remark as for first segment.

11) Key segmentinstallation.

Use of template prevents:

- tearing of waterproofing gaskets.

- concrete chipping.

- greasing of waterproofing gaskets.

It should be noted that oncompletion of erection, the ring isstabilized by the prestress betweenthe erection jacks and the

previously installed ring.

The only contact between theshield tail and 1 the segmentallining is the shield tail seal.



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4.3.2.5 Backfill Grouting

Backfill grouting is the grouting work to fill the annular void between segments andthe ground (tail void) by grout injection. In the case of segmental TBMs, the lining and

its backgrouting are inseparable from the operation of the machine. Because of their interfaces with the machine, they must be designed in parallel and in interdependencewith the TBM.

Mix alternatives could be:

- Cement water

- Cement mortar (sand)

- Slurry (cement - bentonite)

- Inert mortar - Pea-gravel and cement

- Clay (Russia)

In the early days backfilling consisted of either pea gravel or fast-setting or fast-hardening cement slurry or mortar that was injected intermittently through holes in thesegments.

There has been a constant trend to continuously and directly inject products withretarded set and low compressive strength into the annular space directly behind the

TBM tailskin by means of grout pipes routed through the tailskin (Figure 83). Giventhe shield wall/can thickness of 45 ÷ 60 mm, grouting pipes diameter may be in therange of 20 ÷ 25 mm. Consideration should be given to preventing backflow of soiland grout or water into the injection piping as grouting takes place; grease is soinjected between tail seals as a tail packing material. Tail seals should be replaceable incase tail seals are damaged and grout material intrudes into the tail shield.

Figure 83: Longitudinal grout injection through the tailof slurry shield (Gruebl, 2006)



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Requirements for the filling material may be as follows:

- Good pumpable (high content of fine parts, bentonite)

- Enough strength (> 10 MN/m2

) but lower than concrete strength and to keepvolume under loads

- Mortar must loose parts of mixing water to get an early setting behaviour (toavoid flowing around the tail skin to the front)

- Early hardening to avoid movements of the invert segment, when the firsttrailer arrives

- Support of the segment sealing to make the ring watertight

Machine advance is only possible if grouting mortar is available in the requiredamount and at the specified pressure. Carefully controlled grouting will help to avoidalmost entirely significant settlements at the ground surface in the region of the TBM.

For slurry shields, both slurry and grout pressures have impact on ground controlduring construction. Mansour (1996) has found that, the grout pressure is responsiblefor the control of final ground settlements. Although these settlements are alwaysattributed to low grout pressure, extremely high grout pressure that causes localyielding for soil at the crown level, may cause ground surface settlements as well.Therefore, optimization of grout pressure value is essential to efficiently control thefinal ground settlements. The slurry pressure is also responsible for controllingexcessive deformations at the tunnel face and maintaining its stability against plasticfailure.

From experience, it is found that 80 ÷ 90% damage to the segment was due to grouting(e.g. excessive grouting pressure). So control of the grouting pump as well as assemblyof tailsealing (wire brush) is very important (Figure 84).

Because of the permeation to the ground, penetration to the ground by the injection pressure, dehydration, and over cut, the injection volume often becomes 150 - 200 %of the theoretical void volume (sectional area of the shield machine minus sectionalarea of the segment ring). It is desirable to control backfill grouting using both pressure

and volume.

In the absence of annular grouting, bending tensile cracks of the segments may happen.Incorrect grouting can cause steps in annular joints between the segments.

It is common that after lining is grouted on the shield tail (primary grouting), groutingvolume will settle, opening a gap on the upper part of cross section. This gap spaceshould be grouted again, it is called secondary grouting. Secondary grouting may have

bad effects on the tunnel lining segments, therefore this must be taken into account.Secondary grouting is usually undertaken within 20 m of the last ring built. Usuallyvoids will be found in the crown but other areas also need to be checked particularly if

fast setting grouts are used.



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Figure 84: Key segment is pushed out by excessive grouting pressure(Dal Negro, 2006)

Tertiary grouting is sometimes necessary too. It is carried out following evidence of voids in secondary grouting. Other evidences include tunnel leaks, lining movement,

previous high amounts pumped in, grout washed out, grout shrinks. Tertiary groutingis also decided based on the result of drilling through the lining to check for voids.

4.3.2.6 Back-up System

The equipment needed to enable the TBM to perform the excavation are located onmobile platforms which follow the machine and as a whole are called back-up. Someof the back-up equipment and plants installed include:

- Mucking out system (conveyors)

- Muck cars movers or muck conveyor extension system

- Segmental lining handling and erection system or supports erection system

- Equipment for rails and service lines extension

One of the functions of the lining is to support the back-up equipment and construction plant required for carrying out the work. The railway track needs to be placed in theworking area on the back-up, or a temporary roadway in the case of transport of muck

by truck. The track should be properly anchored to the invert segment in order tominimize the derailment hazard.

The following operations within the back-up which may result in potential risks to thelining must be taken into account:

- segment delivering to erection machine;

- erector movement;- segment positioning and erection;



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- back-up maintenance;

- mucking train arriving/leaving;

4.3.2.7 Monitoring and Instrumentation

Monitoring consists of a set of several in-situ measurements of the displacements, thestresses and the strains variations which occur in the ground and in the tunnel supportsduring the excavation procedures. Monitoring is the only mean, in a context of greatvariability and uncertainty, of allowing the excavation of a tunnel to be adjusted in anobjective way during work procedures. By employing this kind of observationalmethod, safety in underground construction could be ensured at the highest level.Therefore monitoring has an essential role in tunnelling. A tunnel design and the

tunnel construction cannot exist without monitoring. Monitoring is the mirror thatreflects the soul of a tunnel (Pelizza, 2006).

Conditions of the works during shield driving shall be monitored or measured to securethe safety of construction. In other words, during construction of tunnel tubes, theinteraction between tunnel segments, and the influence of the surrounding soil on thetunnel lining and vice versa, should be registered. This can be done by incorporatingmeasuring systems in some tunnel rings of the tube.

The monitoring and measurement in shield tunneling works include the following(JSCE, 1996):

1) Monitoring:i) For a closed-face type shield: Earth pressure in the cutter chamber, slurry

pressure at the face, characteristics of the slurry

For an open-face type shield: Conditions of the face, the amount and quality of water inflow

ii) Hydraulic pressure of the jacks, torque of the cutter, meandering and balance of the shield machine, control of the volume and pressure of backfill grout, control of thevolume of excavated soil discharge

iii) Deformation of the shield tunnel and the deviation of the centerline from the

designed alignmentiv) Deformation of the structures and/or underground facilities, displacement of

the ground and variation of groundwater level

2) Measurement: Stress and displacement occurring within the shield machine or lining, and earth pressure and water pressure acting upon the shield machine or lining

Tunnel lining monitoring is now being challenged by automatic data acquisition,which offers many advantages. But, several drawbacks inherent in the use of automaticdata acquisition should also be mentioned. These include the danger of systematic lossof data, the recording box spatial requirements, and possible problem of energy supply

and independence. Further, all monitoring schedules must specify for the interpretation



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of results; if this interpretation stage is neglected, the validity of the monitoring systemmust be questioned.

Concluding Notes

The installation and long term stability of the segmental lining are possible only because the lining is installed with the use of a TBM. The lining is loaded in such away which is strictly linked to the excavation and installation process (thrust of the

jacks, longitudinal grout injection, waterproofing). This observation has an apparentimplication if a final and optimized design is to be achieved.

Gruebl (2006) emphasized that, in a circular bedded segmental ring, deformationsfurther than about 50 m behind the TBM hardly ever occur. Virtually all the significantdamage occurs during ring installation and advance of the TBM in the last 3 to 4, atmost 10, rings. The bearing strength of the segmental ring is rarely exceeded, but

damage can occur to the lining due to incorrect ring erection or insufficient grouting.The cost of repairing the damage may rather high and make a well calculatedconstruction project into an economic failure.

We may conclude that none of the above presented contractual and physical interfacescan be underestimated and overlooked.



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Chapter 5

5. Information for Settlement Study

5.1 Ground Conditions

Lot H3-4 has a total length of 5.8 km, with a minimum overburden of approx. 8.5 m.Figure 85 shows the geometry of the typical cross section with the details of every soillayers. Maximum calculation water level is 28.4 m; minimum calculation water level is17.5 m

Figure 85: Typical cross-section RQ2, homogeneous zone Nr.4Km 33+480 to 33+800



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In Table 11 the ground layers and the corresponding soil characteristic values arelisted.

Table 11: Geomechanical parameters of Lot H3-4

Soil type /

Parameters

GA_T1Coarse-grainedGravel

GA_T2Mixedsand -gravel

GA_T3Fine sand- medium

sand

GA_T4Silt -

fine sand

GA_T6Valley

sand andsilt

Wetdensity

γ [kN/m3]

21 21 21 20 20

Submerged

density

γ’

[kN/m3] 12 12 11 10 10

Drydensity

γd [kN/m3]

18,64 18,64 18,64 17,66 17,0

Voids [−] 0,43 0,43 0,43 0,54 0,54

Frictionangle

φ [°] 37 35 33 30 30

Cohesion c[kN/m2]

0 0 0 0 0

E-ModulusE

[MN/m2]f(z) f(z) f(z) 22,5 10

Poisson'sratio

μ [-] 0,3 0,3 0,3 0,3 0,3

The depth-dependent moduli of elasticity of soil layers GA_T1, GA_T2, and GA_T3are provided by the formula:

f(z) = 0.1 v (0.13 z)w [MN/m2]

determined with v = 373 and w = 0,65 and will be given in Appendix 4.



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5.2 Excavation and Support

5.2.1 Shield Machine

The tunnel has an outside diameter of 12.63 m, to be driven by a Herrenknecht Hydro-Shield TBM with a diameter of approx. 12.98 m, a length of 11.35 m. The totalexcavation area is approx. 132 m2 (Figure 86).

Figure 86: TBM intended for use in Lot H3-4 of the BEG tunnel project

The TBM will be designed, manufactured and operated in accordance with theContract Specification which will define “best practice” for the project. The timerequired to procure, manufacture and deliver a TBM is more than one year. Delivery of the TBM to the Lot H3-4 worksite can be expected in the middle of 2007.

The hydraulic jacks push the TBM forward against the lining of the tunnel behind themachine while excavation is in progress. There are 21 groups (pairs) of hydraulic

jacks, over 21 pads, equally distributed over the circumference of the shield. Each pair consists of two thrust jacks. The feet of the jacks are placed onto the rings. When the jacks are extended, the TBM is pushed forward. After the length of one ring is bored,the jacks are relaxed and the next ring installed.

Excavation diameter : 12.98 m

Outer diameter of structural lining : 12.63 m

Inner diameter of structural lining : 11.63 m

Inner diameter of fireproof lining : 11.23 m



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Weight of TBM : 2,350 T

Total thrust pressure : 10,345 kN

No. of thrusts : 42

No. of pads : 21Pressure/pad : 4,926 kN

Pad geometry (supposed only) : 197 mm x 950 mm

Pressure of the support fluid : 3.5 bars (350 kN/m2)

Grouting pressure (regular) : 2.5 bars (250 kN/m2)

Grouting pressure (accidental) : 4 bars (400 kN/m2)

Allowable space for segment installation is about 2.5 m, including the width of segment (2.0 m). Grouting is provided on the shield tail.

5.2.2 Ring Configuration

The linings will be designed to withstand temporary and permanent loading includingloads from the surrounding ground, groundwater, a surcharge/traffic live load of about100 kN/m2 from the Highway A12, and to meet fire and durability requirements.

The lining's internal diameter of 11.23 meters is sufficient to accommodate the crosssection of the two trains plus lateral movement tolerances, overhead power supply,evacuation and access walkways, resilient and floating track slab, signallingequipment, cables and cable brackets and construction tolerances.

The pre-cast concrete segments reinforced with traditional steel reinforcement will bedesigned to provide a robust solution capable of dealing with the handling loads fromconstruction and the permanent loads from the ground. Segments are to be boltedtogether with suitable gaskets, and the annulus between the lining and the excavatedground is to be filled with grout.

The 0.5 m thick outer structural lining comprises of 7 main segments (with 5rectangular segments and 2 trapezoidal segments) and one keystone segment. Lininggeometry is defined through segment types A1-A5, B, C and K. Segment length is 5.44m, segment width is 2.0 m.

The inner fire protection lining has a thickness of 0.2 m, made of cast-in-placeconcrete. Between the two lining layers is a thin layer of shotcrete for the levelling

purpose. The tunnel inner radius is 5,615 m (diameter 11.23 m), and the opening areais 99.00 m2.

Figure 87 shows the interior fittings inside a cross-section of the Lot H3-4; the rescue

tunnel and escape shaft as shown in Figure 88 will not be considered here.



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Figure 87: Typical cross-section of Lot H3-4, Münster - Wiesing

Figure 88: Cross section with rescue tunnel and escape shaft. Lot H3-4 Münster -

Wiesing



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5.2.3 Lining Material

Concrete material is specified to be Class C 50/60. The steel grade is considered withclass BSt 550. Concrete cover for reinforcement is basically 4 cm thick. Effectiveheight h1 is determined in accordance with Austrian Standard ÖNorm B 4700depending on the used reinforcement. Dead specific weight of the concrete tunnellining of 25 kN/m3 will be used for computation. Gasket will be of Phönix M 385 73Type (Figure 89).

Material properties are defined as follows:

Concrete class : C 50/60

Compressive strength f c28 : 50/58 MPa

(MN/m2)

Specific weight γ : 25 kN/m3

Concrete elasticity modulus E b : 37,000 MPa

Steel elasticity modulus Es : 200,000 MPa

Gasket type : Phönix M 385 73 Typ"Wesertunnel" 618g/m

Gasket width : 44 mm

Elastic capacity : 46 kN/m

Max. tested closed gap : 15 mm

Figure 89: Gasket dimensions for Lot H3-4



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5.3 Numerical Analysis Tool

The tunnel of the BEG Lot H3-4 crosses the Inn River with low overburden, as well asthe motorway A12 and the existing tracks of the Austrian Railway. Some informationon the statical calculations of the tunnel is presented in the following.

For the purpose of reference only, below are given the software actually utilized by theDesigner for the BEG project:

- Z_SOIL.PC 2003 V 6.24 Professional software: "Soil, rock and StructuralMechanics in dry or partially saturated media" (Zace services Ltd.)

- RSTAB V 5.12.058: "statics of general structures". The designing firm madecalculations of the lining by this RSTAB program (Ing. - software Dlubal

GmbH)

- RFEM 2 V 2.01.135: "spatial lining units according to the method of the finiteelements" (Ing. - software Dlubal GmbH)

- ConDim 5 concrete calculation, version: 5.04 (DI Dr. Lorenz)

However, in this work, the author will make use of PLAXIS, a finite element code for soil and rock analyses of Plaxis B.V. Netherlands, to perform independent parameter studies. The parametric calculations are to partly illustrate the theoretical points thathave been presented in the previous parts of this report. Calculations focused on the

Austrian BEG project's TBM Lot H3-4.

5.3.1 Soil Models in Plaxis

Plaxis offers a variety of soil models in addition to the Mohr-Coulomb model. Thelogarithmic compression behaviour of normally consolidated soft soils can beaccurately analysed by Cam-Clay type model (Soft Soil model), or by an improvedversion of it for secondary compression (creep). For stiffer soils, such asoverconsolidated clays and sand, an elastoplastic type of hyperbolic model is available,which is called the Hardening Soil model.

Short descriptions of the available models are given below.

L inear elastic model:

This model represents Hooke's law of isotropic linear elasticity. The model involvestwo elastic stiffness parameters, namely Young's modulus, E , and Poisson's ratio, ν.The linear elastic model is very limited for the simulation of soil behaviour. It is

primarily used for stiff massive structures in the soil.



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What is stiffness? The link between strain increments ε and stress increments σ will berequired for performance of numerical analysis of geotechnical systems; then astiffness matrix D is formally required to be developed and populated: δσ = D δε, andthis incremental link between stress and strain is the most useful definition of stiffness.

Mohr-Coulomb model:

This well known model is used as a first approximation of soil behaviour in general.The model involves five parameters, namely Young's modulus, E , Poisson's ratio, ν,the cohesion, c, the friction angle, φ, and the dilatancy angle, ψ. What is dilatancy? If the arrangement of the soil particles is disturbed by distorting the boundary of the soilsample then rearrangement will be accompanied by some change in the volumetric

packing: this is dilatancy.

All different soil layers can be modelled by the simple Mohr-Coulomb model. For

settlement analyses, the Hardening Soil model may be preferred, but for tunnelheading stability the focus is on soil strength and not on soil stiffness

Hardening Soil (HS) model:

This is an elastoplastic type of hyperbolic model, formulated in the framework of friction hardening plasticity. This second-order model can be used to simulate the

behaviour of sands, gravel and overconsolidated clays.

Soft Soil model:

This is a Cam-Clay type model which can be used to simulate the behaviour of softsoils like normally consolidated clays and peat. The model performs best in situationsof primary compression.

Soft Soil creep model:

This is a second order model formulated in the framework of viscoplasticity. Themodel can be used to simulate the time-dependent behaviour of soft soils.

In the following parts, only Hardening Soil model will be utilized for the purpose of this report's parametric studies.

5.3.2 Hardening Soil Model

The Hardening-Soil model (isotropic hardening) is used for simulating the behaviour of different types of soil, both soft soils and stiff soils. This model uses the theory of

plasticity rather than the theory of elasticity; it also includes soil dilatancy andintroduces a yield cap.



126

The Hardening-Soil model represents a much more advanced model than the Mohr-Coulomb model. As for the Mohr-Coulomb model, limiting states of stress aredescribed by means of the friction angle, φ, the cohesion, c, and the dilatancy angle, ψ.Soil stiffness is described much more accurately by using three different inputstiffnesses:

¾ the triaxial loading stiffness, E 50 (characteristic of plastic straining due to primary deviatoric loading);

¾ the triaxial unloading stiffness, E ur (characteristic of elastic unloading /reloading, Figure 90); and

¾ the oedometer loading stiffness, E oed (characteristic of plastic straining due to primary compression, Figure 91).

Figure 90: Hyperbolic stress-strain relation in primary loading for a standard drainedtriaxial test. qa is the asymptotic value of the shear strength, qf is ultimate deviatoric

stress

Figure 91: Definition of tangent stiffness modulus ref

oed E in oedometer test results



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As average values for various soil types, we have E ur ≈ 3 E 50 and E oed ≈ E 50, but bothvery soft and very stiff soils tend to give other ratios of E oed / E 50. In contrast to theMohr-Coulomb model, the Hardening-Soil model also accounts for stress-dependencyof stiffness moduli. This means that all stiffnesses increase with pressure. Hence, allthree input stiffnesses relate to a reference stress, pref or σref , being usually taken as 100

kPa (1 bar).

For virgin oedometer loading, soil behaviour simulated by the HS-Model implies anincreasing tangent stiffness modulus according to

( )1. /( )m

ref

oed oed ref E a aσ σ ⎡ ⎤= + +⎣ ⎦

where a = c.cotφ, 1σ is the major principal stress, and ref

oed E is the reference tangent

stiffness for primary oedometer loading. We adopted the exponent m = 0.5 (stressdependent stiffness according to a power law). Within the HS Model unloading-

reloading is described on the basis of Hooke’s law. Young’s unloading-reloadingmodulus for increments of stress and strain is:

3 cot.

cot

m

ref

ur ur ref

c E E

c

σ ϕ

σ ϕ

⎛ ⎞+= ⎜ ⎟

+⎝ ⎠

where 3σ is the minor principal stress, ref

ur E is the reference Young's modulus for

unloading and reloading, corresponding to the reference pressure σ ref . In many practical cases it is appropriate to set ref

ur E equal to 3 50

ref E .

For many problems, especially excavation problems, there is a preference to use theHardening-Soil model (HS-model) rather than the Soft-Soil model (SS-model).

5.4 Flowchart of Calculation

Surface settlements will be checked both with analytical and numerical methods.

Variation of input parameters based on “greenfield” condition will be performed inorder to check the respective output results, using the Hardening Soil model(symmetrical).

Parameter studies for the “greenfield” cross-section will be carried out as follows:

1) Using semi-empirical methods to calculate the surface settlement, with the actualgeological and lining information of the BEG project.

2) By using Plaxis code, the factor of contraction (volume loss) will be graduallyvaried, starting with a value of 0.5 %, then stepwise increasing with an incrementof 0.25% until convergence is achieved. The number of elements of the FE net

(the mesh) will be varied starting from about 500 elements up to approx. 1,000elements, with an increment of around 200 elements for each step. The



128

combination of the two varying variables (the contraction and the meshcoarseness) will involve many computation cases.

3) Variation of the lining thickness will be carried out in the range of 0.30 m ÷ 0.60m, stepwise thickness increase = 0.10 m (i.e. t = 30, 40, 50, and 60 cm). The

mesh coarseness is also varied accordingly. Next, final settlements will becalculated, using the design lining thickness of 50 cm and with the convergedcontraction value attained at the step 1.

4) Compare the calculated results of settlements by both analytical and numericalmethods for the case of actual project input data.

5) 3D modelling of the shield tunnel face stability is performed.

Such variations help to check the sensitivity and reliability of the results of face

stability and ground settlements corresponding to the input parameters associated withthe various analysis methods. These parameter studies supplement some interfaceaspects concerning the tunnel design and construction presented in the previouschapters.



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Chapter 6

6. Tunnel Induced Ground

Deformation

6.1 Settlement Induced by Tunnelling

6.1.1 Volume Loss and Settlement

- Ground movements and volume loss due to tunnelling

All sub-surface excavations give rise to ground movement. In other words, groundmovements are an inevitable consequence of constructing a tunnel. These movementsmanifest themselves, in particular, as settlement. It is not possible to create a voidinstantaneously and provide an infinitely stiff lining to fill it exactly. In the time taken

to excavate, the ground around the tunnel is able to displace inwards as the stress relief is taking place (Figure 92). Thus it will always be necessary to remove a larger volumeof ground than the volume of the finished void. This extra volume excavated is termedthe "Volume Loss" (or "ground loss", "soil loss") VL (Chiriotti, 2006).

Figure 92: Inward displacement of the ground around the tunnel

due to stress relief (Chiriotti, 2006)



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For the construction of tunnel, the overall volume loss VL consists of two components:face loss and radial loss (radial displacements around the shield section and around thelining section, Figure 93) [m3/meter advance of the tunnel drive].

Figure 93: Components of the volume loss or the convergence generated by tunnellingwork (Chiriotti, 2006)

In a properly supported non-TBM tunnel, 70-80% of total surface settlement is due todeformations ahead of tunnel face. In a shield-driven excavation, the fraction variessignificantly (<< 70%) depending on the method. As an example, until a recent date,the following distribution of settlements to the surface was observed:

- 10 to 20 % caused by the face;

- 40 to 50 % caused by the void along the shield;

- 30 to 50 % caused at the end of the tail seal.

But thanks to the current technological and methodological evolutions, these arechanging and settlements at the tail seal exit may only stand for a small part of the totalsettlements (AFTES, 1995).

The net volume of the surface settlement trough will be approximately equal to thevolume loss at the tunnel in most ground conditions. If the ground response is atconstant volume (i.e. undrained), the relationship will be exact. The hypothesis will bechecked especially if the ground is clayish and the overburden is thin. Otherwise,relationship between the displacement in the tunnel crown (Urcrown) and the middlesurface settlement (Smax) can be referred to Figure 94 as an example, where C isoverburden thickness above the crown, and D is excavation diameter.

INSTALLED RINGS

EXCAVATIONCHAMBER

SHIELD

SCREWCONVEYOR

RADIAL INJECTION BEAD

FACELOSS

RADIAL LOSS - shieldRADIAL LOSS - annulus



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Figure 94: Softening coefficient according to the geometry of the tunnel bored with a shield (AFTES, 1995)

V L is normally expressed as a percentage V L% of the gross area of the finished tunnel.

Assuming a circular tunnel of outside diameter d , then

2

100% 100%%

4 L L

L

tunnel

V V V

V d π

× ×= =

The magnitude of the volume loss VL depends on many different factors:

soil type

tunnelling method

rate of tunnel advance

tunnel size form of temporary and primary support

Before the magnitude of ground movements can be predicted it is necessary to estimatethe expected ground loss. This estimate will be based on case history data and shouldinclude an engineering appraisal that takes into account the proposed tunnellingmethod and site conditions.

NATM:

London Clay → VL% = 0.5% - 1.5%

which compares favourably with controlled shield tunnelling



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Open face tunnelling

Stiff clay → VL% = 1% and 2%

Closed face tunnelling (EPB or slurry shields): A high degree of settlement control can be achieved.

Sands → VL% < 0.5% (0.35% can be achieved with slurry shield and EPBTBM tunneling).

Soft clays → VL% = 1% - 2% (excluding consolidation settlements)

- Short, medium and long term movements

SHORT-TERM ground movements are identified to occur during the excavation, at atimescale that is comparable with the time taken by the advance of the tunnel heading

that is the cause of ground movements.MEDIUM and LONG-TERM settlements are thought to be the result of creep, ageingand consolidation, i.e. alterations in the properties of the soil at constant load. Thetimescale over which they occur depends on the ground conditions, ranging fromweeks or months (sands and soft clays) to years (stiff clays).

The magnitude of long-term movements is hard to generalise. The long-termsettlement trough widths are observed to have tendency to be wider than that of theshort-term settlement trough widths. This means that the curvature of the trough, thefactor most likely to cause damage to the structures on the surface, is smoother.

In addition, surface structures are more able to accommodate long-term settlements bycreep and stress redistribution. Thus it is the short-term movements that remain thechief issue of concern for engineers, and are the subject of this study.

- Rock-tunnelling movements

Rock tunnels may not be immune from causing unacceptable ground movementswhere water inflow may, by way of the jointing system, cause draw-down inoverlaying fine sediments (Peila, 2006).

6.1.2 Settlement Calculation Approaches

Short literature review

Leca and Dormieux (1990) have used the upper and lower bound theorems of plasticityto estimate the pressure, which can be provided by compressed air, slurry or an earth

pressure balance (EPB) tunnelling machine, needed either to ensure stability or obviate blow-out of the tunnel heading in soft ground.



133

Suwansawat (2002) and Suwansawat & Einstein (2006) have attempted to predictground response and the maximum surface settlement caused by EPB shield tunnellingusing artificial neural networks (ANN), at the same time to evaluate the potential aswell as the limitations of ANN for that purposes.

The empirical method have been proposed by a number of authors, such as New &O'Reilly (1982, 1991), Attewell and Woodman (1982), etc. to predict the settlement for “green-field” site conditions induced by bored tunnels. Semi-empirical method usesthe parameters for ground loss determined from case histories and take into account themethod of tunnelling and ground conditions; they are still being widely used today.

Recently, a generic area-wide assessment of settlement identifies zones in which buildings might be at risk of sustaining damage in excess of acceptable levels based oncorrelation with the calculated maximum tensile strain values (Franzius 2003, 2005).The potential for damage in this area-wide assessment can be defined using the

procedure described by Mair et al (1996).

On the other hand, numerical methods, mainly the Finite Element Method (FEM), provide a flexible tool for a prediction of surface settlement, which have been adopted by many authors. FEM could be performed in two-dimensional (2D) or three-dimensional (3D).

In the past, Selby (1988) recommended that the empirical equations should be used for predictive purposes as they compared well with field measurements and were mucheasier to use than the finite element model.

Clough and Leca (1989) have pointed out that the soil tunnelling problem has provedresistant to finite element (FE) modelling because it is complex, often involves

parameters that are not well defined and is unforgiving if the analyst does not properlymodel both the soil and the tunnel supports, as well as the construction process. Thesensitivity of the FE method to these factors has meant that it is a less reliable methodfor ground movement prediction than the empirical approach.

However, New and Reilly (1991) deemed that the flexibility of FE models can beexploited when back analyzing ground movements and can assist in understanding themovements at particular sites and by extending conventional design techniques.

Indeed, the numerical methods (e.g. FEM) have been being more and more powerfuland reliable as a consequence of advances in computer technology.

Selected Calculation Approach

In the following, the author will try to apply the two main settlement predictionapproaches: (i) analytical/semi-empirical, based on empirical formulas derived from

past observations; and (ii) finite element analysis, which is now rather popular method.



134

6.1.3 Settlement Control Approach

After prediction of settlements is completed, the other considerations to minimizesettlement affecting buildings above include:

¾ Monitoring;

¾ Protective works;

¾ Defects surveys; and

¾ Repairs

i) Monitoring

Design for a plan of ground and surface monitoring plays a significant role inmanaging settlement and damage. The scope of monitoring should be set up for thetwo main categories: ground and buildings. In the monitoring plan, the governing

parameters shall be defined, and the necessary instruments shall be selected. Thecriteria for the attention and alarm limits (threshold values) shall also be established.Then, based on monitoring, if any critical scenario is detected, counter-measures will

be triggered accordingly. Relation between the three main elements: designhypotheses, monitoring, and countermeasures, is given in Figure 95.

Figure 95: Monitoring in relation with other procedures (after Chiriotti, 2006)

ii) Protective measures

Tunnelling-induced subsidence can be mitigated and controlled by means of (Cross

London, 2005):

Designhypotheses

Monitoring

Countermeasures



135

• Good tunnelling practice (including continuous working, erecting liningsimmediately after excavation and providing tight control of the tunnelling

process to reduce the magnitude of settlement);

• At-source measures (including all actions taken from within the tunnel

during its construction to reduce the magnitude of ground movementsgenerated at source, such as face stability, backfill grouting at shield tail,etc.);

• Ground treatment measures (including compensation grouting, permeationor jet grouting, control of ground water, etc.);

• Structural measures (to reduce the impact of ground movements byincreasing the capacity of a building or structure, typically includingunderpinning or jacking/shoring).

iii) Defect surveys (condition of properties)

Defect surveys are typically undertaken 1 month before construction starts in the areato capture the condition of all properties immediately prior to tunnel construction. It isnecessary to use a reliable damage classification system for masonry structures withthe concept of limiting tensile strain. A staged process of assessing risk may beadopted, including preliminary assessment, second stage assessment, and detailedevaluation. In this process, buildings are eliminated from further stages depending onthe potential degree of damage predicted (Mair et al, 1996).

iv) Repairs

If the damage is caused by the nominated undertaker’s works, the nominatedundertaker has to reimburse property owners for the reasonable cost they incur inremedying material physical damage arising from ground settlement caused by theauthorized works.

6.2 Empirical Calculation for Settlement

6.2.1 Formulae

Single tunnels:

Usually, the first stage of settlement assessment is based on "green-field" siteconditions. This means that there is no existing surface building or underground

structure, or the effect of building foundations on the pattern of settlement is ignored.



136

Peck (1969) described settlement data from over 20 case histories available to him atthat time, and was able to deduce that the short-term transverse settlement trough in the"greenfield" could be approximated by a Gaussian curve (same as O’Reilly, 1982)(Figure 96):

2

max 2exp

2 yS S i

⎛ ⎞−= ⎜ ⎟⎝ ⎠

(O’Reilly, 1982)

where,

S = theoretical surface settlement (the Gauss error function, or normal probability curve) (m)

Smax = maximum surface settlement (over tunnel axis, i.e. the settlement trough

depth) (m)

22

Lmax L

V 0.313V (%). 1S = V (%). .42 i 2 i

S

D D

i

π

π π = = (New & O’Reilly, 1991/

Mair et al, 1996)

( )2

max 00.785. . ..

s

DS Z P

i E γ

⎛ ⎞= + ⎜ ⎟

⎝ ⎠(Herzog, 1985)

This equation for Smax was derived from both shield excavated and NATM tunnel data(Arioglu, 1992, quoted by Ercelebi, 2005).

y = transverse horizontal distance from the tunnel centerline (m)

i = standard deviation of the curve (point of inflexion of the curve) (m); atrough width parameter which can be calculated after O’Reilly and New(1982) or Arioglu (1992) as in the following section

γ = (average) natural unit weight of formation (ton/m3)

z 0 = tunnel axis depth (m)

Ps = total surcharge load (ton/m2)

D = equivalent tunnel excavation diameter (m)

E = (average) elasticity modulus of formation (ton/m2

)The settlement ordinate at distance i is, according to the properties of the probabilitycurve, equal to 0.61 Smax.



137

Figure 96: Gaussian distribution curve of the short-term transverse settlement trough inthe ‘greenfield’

* Note : According to Martins (2001), another closed-form analytical solution to

predict surface settlements has also been proposed:

( )( )

22

0 0 22 2

1.384 1 exp z

H yS R

H y H Rε ν =

⎛ ⎞= − −⎜ ⎟

⎜ ⎟+ +⎝ ⎠Loganathan and Poulos (1998)

where ε0 is the ground loss (ratio), ν is the Poisson's ratio of the soil above the tunnel,R is the tunnel radius, H the tunnel depth and y is the lateral distance from the tunnelcentre-line. On the basis of centrifuge testing Loganathan, Poulos and Stewart (1999)claim that this equation gives better results than the Peck's equation.

The Peck/O'Reilly's equations are based on the assumption that the settlement profileabove a single tunnel is of normal probability or Gaussian form. Ground deformationis assumed to take place at constant volume.

The Gaussian curve shown above is used at all levels in the ground above the tunnel.For the combined effect of multiple tunnels, the movements induced by each tunnel aresimply added.

The width of the settlement trough perpendicular to the tunnel is defined in terms of distance 'i' in meters from the tunnel centre-line to the point of inflexion on the curve.

Peck noticed that soils of different classes - e.g. cohesionless or cohesive - gavedistinct ratios of trough width parameter ‘i’ to tunnel depth ‘z0’.



138

Following from this, O’Reilly and New (1982) expressed the trough width parameter ‘i’ in the form:

oi K z =

where,

K = dimensionless empirical constant, depending on the soil type

z0 = depth of the tunnel axis below ground level

Based on data from both cohesive and cohesionless locations, all in the UK, O’Reillyand New (1982) proposed the empirical relationships:

i = 0.43 z 0 + 1.1m ( for cohesive soils)

and

i = 0.28 z 0 - 0.1m ( for non-cohesive soils)The data used covered a wide range of tunnel axis depths. It thus appeared justified totake K as a constant value, independent of both tunnel depth and diameter. Later work

by other researchers has confirmed that K is usually in the range:

K = 0.4 ÷ 0.5 for cohesive soils,

K = 0.25 ÷ 0.35 for cohesionless soils

K values when tunnelling in stratified soils:

If we assume that, all the strata influence the settlement phenomena to the same extent ,then k eq is the average weighted value of the various k i:

z0 < 1.5D ⇒

1 1 ... n neq

tot

z k z k k

z

+ +=

Figure 97: K values when tunnelling in stratified soils with z0 < 1.5D

ztot<1.5D

z1

z2

zn

k 1

k 2

k nD



139

If we assume that, the strata within 1.5D influence are the ones that mainly influence

the settlement phenomena, then k i can be weighted according to their distance from the

tunnel.

z0 >1.5D ⇒

1 1 1 1

1 1

0.35( ... ) 0.65( ... )

0.35( ... ) 0.65( ... )m m m m n n

eq

m m n

z k z k z k z k k

z z z z

+ +

+

+ + + + +=

+ + + + +

Figure 98: K values when tunnelling in stratified soils with z0 > 1.5D

Otherwise, i can be calculated by following formulae:

1 2 3

3

i i ii

+ +=

1 00.386. 2.84i Z = + (Arioglu, 1992)

2 00.5.i Z = (Glossop, 1978)

0.704

03

ZDi = 1.392. .

2 D

⎛ ⎞⎛ ⎞⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠

(Arioglu, 1992)

Under undrained conditions, e.g. in materials with a low permeability such as stiff clay, the volume of the surface settlement trough is equal to the volume of soil whichis excavated in excess of the theoretical volume of the tunnel (constant volume), wehave:

s LV V = ⇒ 2

sL L

tunnel

V .V (%) = V (%).

V 4S

DV

π ⇔ =

where V s = volume of the settlement trough (per metre length of tunnel), so, the loss at

the tunnel level is completely transferred to the surface.‘Vs’ can also be evaluated as the integral of the Gaussian distribution curve:

ztot≥1.5D

k m

z1

z2

k 1

k 2

k n

zm

zn

k m+1

1.5D

zm+1

D



140

2

max 2

- yS = S exp

2i

⎛ ⎞⎜ ⎟⎝ ⎠

⇒ s max maxV = 2 iS = 2.51iSπ

22L

max L

V 0.313V (%). 1S = V (%). .

42 i 2 i

S D D

i

π

π π

= =

The expression for the total vertical settlement due to tunnelling S may be rewritten,substituting for S max, as:

2 2L

max 2 2

V- y - yS = S exp = exp

2i 2ii 2π

⎛ ⎞ ⎛ ⎞⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠

NOTE:

• Under drained conditions (e.g. dense sands) V s is usually less than V L because

of dilation. Sometimes (e.g. loose granular soil) V s could be greater than V L incase of negative dilation.

• The trough width widely depends on the ground characteristics and the projectgeometry (C/D, i.e. overburden thickness C above the crown/excavationdiameter D) and much less on deconfinement which, on the contrary, stronglyinfluences Smax.

It is also conceived that, settlements are a 3D problem. We can be interested inevaluating (i) the transversal settlements trough in a certain section while it isdeveloping; or (ii) the longitudinal settlement trough (Figure 99 and Fig. 100).

Figure 99: 3D view of settlement trough due to tunnelling (after Attewell et al., 1986)



141

Figure 100: Evolution of settlements along a shield (AFTES, 1995)

Attewell and Woodman (1982) extended this model to derive a settlement trough in thelongitudinal direction, as presented in Figure 101.

According to Attewell and Woodman (1982), the generalized expression for surface

settlements can be written:

2

22

2

y

s i F iV x x x x

S e G G

i iiπ

− ⎧ − ⎫−⎡ ⎤ ⎡ ⎤= ⋅ ⋅ −⎨ ⎬⎢ ⎥ ⎢ ⎥

⋅ ⎣ ⎦⎣ ⎦⎩ ⎭

where:

S = surface vertical settlement at a location defined by the coordinates (x,y) [m];

y = transverse distance of the considered surface point from the tunnel centerline [m];

x = longitudinal position of the considered surface point [m];

Vs = volume of the settlement trough per meter of tunnel advance [m3/m], defined as a

percentage VL of Vtunnel;

xi = initial position or starting section of the tunnel [m];

xf = considered position of the tunnel face [m];

‘G’ is a function defined as:

( )

2

21

2G e d

α α

α α π

−

−∞

= ⋅ ∫ , with α = (x-xi)/i

G(0) = 0.5 when x = xf (point above the tunnel face)

G(1) = 1.0 when (x-xi) → ∞



142

Figure 101: Settlement trough in the longitudinal and transversal direction

Figure 102: Definition of ‘G’ function

(x-xf )/i

0

G[(x-xf )/i]

g[(x-xf )/i]

3

Smax

Initial section

xi

Tunnel face

x

½ Smax

S

Smax

Yi

Tunnel axis

Considered section for subsidence calculation in

a cross-section

Xxf xxi

LONGITUDINAL SETTLEMENT

TRANSVERSAL SETTLEMENT

G1=1 and G0=0 G1=1 and G0≠ 0



143

Values of the G function have been already calculated for different values of (x-xi)/iand they are available in the format of table.

The subsidence profile in a longitudinal section is evaluated on the basis of the abovegeneral equation. Being y = 0 along the tunnel axis the expression becomes:

( )max 1 22

s i F V x x x x

S G G S G Gi iiπ

⎧ − ⎫−⎡ ⎤ ⎡ ⎤= ⋅ − = ⋅ −⎨ ⎬⎢ ⎥ ⎢ ⎥⋅ ⎣ ⎦⎣ ⎦⎩ ⎭

If the starting tunnel position xi and the position of the face xF are known, then it is

possible to calculate the vertical displacement for different points located ahead (x >xF) or behind (x < xF) the tunnel face.

When G1 = 1 and G0 ≠ 0 the longitudinal displacement is a percentage of Smax, being

the difference G1 - G2 < 1. The settlement directly above the tunnel face corresponds

to 0.5Smax (Figure 56).

For completeness, we like to mention a personal opinion of Prof. Swoboda (personalcommunication), that for Smax one has to use FEM; he found out only with 3D modelsone can get good displacement results for TBM; for NATM one can do it with a 2Dmodel.

* Horizontal surface displacements:

Damages to above ground structures could also result from horizontal grounddeformations induced by tunneling. It is assumed (Mair et al., 1996) that the horizontalsurface displacement sh(y) at a distance y from the tunnel center-plane can bereasonably expressed as:

( ) ( )h

y s y S y

H =

where H is the depth to tunnel axis and S(y) the settlement at a distance y from thetunnel center-plane.

Twin tunnels:

The construction of twin tunnels is a common requirement for underground railwaysand there exist useful equations for making preliminary ground movement predictions.In practice the tunnels will rarely be driven simultaneously and one tunnel is likely tohave been excavated significantly before the other. In some cases this will give rise toan asymmetry which is not modelled by the equations.

It is generally assumed that the predicted ground movements for each tunnel can besuperimposed. For twin tunnels with reduced transversal distance between the axes thisassumption may be unconservative. Disturbance due to the first tunnel drive can be



144

simulated by assuming a greater volume loss for the second bore and superimposingthe resulting ground movements.

For the configuration shown in Figure 103 the settlement resulting from the combinedeffects of the twin tunnels is given by

( )

( )22

, 2 2exp exp

2 22S

y z

y DV yS

i ii π

⎡ ⎤⎛ ⎞−⎛ ⎞⎢ ⎥= − + −⎜ ⎟⎜ ⎟ ⎜ ⎟⎢ ⎥⎝ ⎠ ⎝ ⎠⎣ ⎦

(New and O'Reilly, 1991)

Figure 103: Surface settlement profile for twin tunnels (New and O'Reilly, 1991)

If two or more shield tunnels are constructed side by side or on top of one another,ground movement and tunnel movement shall be carefully observed. If necessary,auxiliary methods shall be taken in order to prevent ground relaxation and tunneldeformation.

6.2.2 Calculated Results

TBM machine has an excavation diameter of De = 12.98 m, and tunnel lining has anoutside diameter of Dl = 12.63 m. Therefore, the ground loss due to overcut (in theworst case possible, i.e. without control by annular grouting) is given by:

2 2

2% 100%e l

L

l

D DV x

D

−= = 5.62 % ⇒

2

L

.V (%).

4S

DV

π = = 7.04 m3/m



145

De (m) Dl (m)Ground loss

VL (%)

Settlementtrough volume

VS (m3/m)

Annular gap (cm)

12.98 12.63 5.62 7.04 17.5

Area (m2) 132.32 125.28 7.04

Using the empirical formula of Herzog (1985)

( )2

max 00.785. . ..

s

DS Z P

i E γ

⎛ ⎞= + ⎜ ⎟

⎝ ⎠

The maximum settlements Smax are shown in Table 12. In this calculation, averagemodulus of elasticity of the overburden E is taken from Appendix 4 as 32.4 MN/m2 or 3,240 ton/m2 and average specific weight γ is taken as 2.06 T/m3.

The maximum settlement Smax = 148 mm seem to be rather large. The deduced volume

of the settlement trough Vs = 4.35 m3/m, and the ground loss VL = 0.035 %. Althoughthe volume loss is small, but the maximum settlement is in practice large; therefore,the settlement must still be controlled by high quality backfill grouting duringconstruction. Figure 104 shows the shape of settlement trough.

Table 12: Estimation of settlement by empirical formula of Herzog (1985)

Input Estimations (m)D = 12.63m i1 = 11.25

Z 0 = 21.8m i2 = 10.90γ = 2.06tonne/m3 i3 = 12.91

E = 3,240tonne/m2 i = 11.69 P s = 0.0tonne/m2 Smax = 0.148C = 15.5m

VS (m3/m) = 4.35

C/D= 1.23shallow tunnel

VL% = 0.035z0/D

= 1.73



146

020

406080

100120140160

- 3 5 .

1

- 3 1 . 7

- 2 9 . 2

- 2 5 . 9

- 2 3 .

4

- 1 9 . 2

- 1 6 . 7

- 1 4 . 2

- 1 1 . 7

- 9 . 2 - 6

. 7 - 4

. 2 - 1

. 7 0 . 0 1 . 7

4 . 2 6 . 7 9 . 2

1 1 . 7 1 4

. 2 1 6

. 7 1 9

. 2 2 3

. 4 2 5

. 9 2 9

. 2 3 1

. 7 3 5

. 1

Distance from Tunnel Center Line (y), m

S e t t l e m e n t ( S )

, m m

Empirically predicted Settlement Curve, volume loss = 0.035%

Figure 104: Settlement prediction for BEG Lot H3-4 tunnel by Herzog formula

Table 13 represents the dependence of the maximum settlements and volume loss onthe modulus of elasticity of soils used in the Herzog formula. Modulus of elasticity Eis varied from 10 MPa to 100 MPa, while keeping surcharge Ps as zero. As a result, themaximum settlements Smax range from 481 mm to 48 mm, and the ground losses VL range from 0.113 % to 0.011 %.

Table 13: Dependence of the maximum settlements and volume loss on the modulus of

elasticity of soils used in the Herzog formula, without surcharge (Ps = 0)

E (MPa) Ps (MPa) Smax (mm) Vs (m3/m) VL (%)

10 0 481 14.10 0.113

20 0 241 7.05 0.056

25.1 0 192 5.62 0.045

30 0 160 4.70 0.038

32.4 0 148 4.35 0.035

40 0 120 3.52 0.028

50 0 96 2.82 0.023

60 0 80 2.35 0.019

70 0 69 2.01 0.016

80 0 60 1.76 0.014

90 0 53 1.57 0.013

100 0 48 1.41 0.011

Next, we impose a surcharge of 0.1 MPa on the surface. As a result, the maximumsettlements Smax range from 588 mm to 59 mm, and the ground losses VL range from

Empirically predictedSmax = 148 mm

"Greenfield" CrossSectionE = 3240 tonne/m2 γ = 2.06 tonne/m3 Ps = 0 tonne/m2 Z0 = 21.8 m



147

0.138 % to 0.014 %. From Table 14, it is found that the maximum settlements S max aretoo large, but the associated volume losses VL are too small. Considering the actualdatabase achieved in practice by the slurry TBM technology, we can conclude thatHerzog formula does not give a good compatibility between the maximum settlementsand the ground losses.

Table 14: Dependence of the maximum settlements and volume losses on the elasticmodulus of soils, Herzog formula, with surcharge Ps = 0.1 MPa

E (MPa) Ps (MPa) Smax (mm) Vs (m3/m) VL (%)

10 0.1 588 17.23 0.138

20 0.1 294 8.62 0.069

24.47 0.1 240 7.04 0.056

30 0.1 196 5.74 0.04630.65 0.1 192 5.62 0.045

32.4 0.1 182 5.32 0.042

40 0.1 147 4.31 0.034

50 0.1 118 3.45 0.028

60 0.1 98 2.87 0.023

70 0.1 84 2.46 0.020

80 0.1 74 2.15 0.017

90 0.1 65 1.91 0.015

100 0.1 59 1.72 0.014

Using O'Reilly & New (1982)/Mair et al (1996) formula

Because Lot H3-4 tunnel is driven through a stratified soil, and because z0 = 21.8 m >1.5D = 18.945 m, so if we choose individual k factor for each layer, after that use theweighted formula of O'Reilly & New (1982) for equivalent k factor, then we have k eq =0.338 (see Table 15).

Table 15: The equivalent factor "K" and the trough width parameter "i" by usingO'Reilly & New (1982) formula

zi (m) k i zi x k i k eq i (m)

Layer 1 GA_T6 1.80 0.40 0.72

Layer 2 GA_T1 4.70 0.35 1.65

Layer 3 GA_T2 6.00 0.32 1.92

Layer 4GA_T3

4.30 0.34 1.46

Layer 5 GA_T3 5.00 0.34 1.70 0.338 7.37 z0 = 21.80



148

Since i = Kz0 therefore we have i = 0.34 x 21.8 m = 7.37 m, much smaller than that of Herzog (1985) formula (i = 11.69 m).

Using the expression2

max

0

0.313 L

V DS

K z = and varying the values of factor K = 0.25 ÷

0.5 (K = 0.25 for tunnels in sands or gravels, and K = 0.5 for tunnels in clay) andvolume losses VL = 0.2 % ÷ 5 %, we can obtain the maximum settlements Smax asshown in Table 16.

Table 16: Maximum settlements for various volume loss and K factor values. New andO'Reilly (1991)/Mair et al (1996) empirical formula

Smax (mm)

K D (m) Z 0 (m)VL

(%)0.25 0.30 0.338 0.40 0.45 0.50

12.63 21.8 0.202 2 1 1 1 1

12.63 21.8 0.25 2 2 2 1 1 112.63 21.8 0.30

3 2 2 2 2 112.63 21.8 0.35 3 3 2 2 2 212.63 21.8 0.40 4 3 3 2 2 212.63 21.8 0.45 4 3 3 3 2 212.63 21.8 0.50 5 4 3 3 3 212.63 21.8 1.00 9 8 7 6 5 512.63 21.8 1.30 12 10 9 7 7 612.63 21.8 1.50 14 11 10 9 8 712.63 21.8 2.00 18 15 14 11 10 912.63 21.8 2.50 23 19 17 14 13 1112.63 21.8 3.00 27 23 20 17 15 1412.63 21.8 3.50 32 26 23 20 18 16

12.63 21.8 4.00 36 30 27 23 20 1812.63 21.8 4.35 39 33 29 25 22 2012.63 21.8 4.50 41 34 30 26 23 2012.63 21.8 5.00 45 38 33 28 25 2312.63 21.8 5.62 51 42 38 32 28 25

Taking an average value of 0.338 for K factor, we have four settlement predictioncurves corresponding to volume losses of 0.5%, 1 %, 1.3 %, and 2 % as shown in

Figure 105.



149

0

5

10

15

- 2 2 .

1

- 2 0 . 9

- 1 8 .

4

- 1 7 . 2

- 1 4 . 7

- 1 2 .

4

- 9 . 9

- 7 . 4

- 4 . 9

- 2 . 4

0 . 0

2 . 4

4 . 9

7 . 4

9 . 9

1 2 . 4

1 4 . 7

1 7 . 2

1 8 . 4 2 0

. 9 2 2

. 1

Distance from Tunnel Center Line (y), m

S e t t l e m e n t ( S ) ,

m m

Volume loss = 0.5 %Volume loss = 1 %Volume loss = 1.3 %Volume loss = 2%

Figure 105: Settlement predictions for BEG Lot H3-4 tunnel by formula of New andO'Reilly (1991)/Mair et al (1996)

The prediction method of O'Reilly & New (1982)/Mair et al (1996) does not accountfor the modulus of elasticity of the soil E as that of Herzog (1985). Therefore, themaximum settlements Smax obtained from two methods are quite different, and they cannot be reasonably compared with one another, because the volumes losses deducedfrom the Herzog formula are always too small.

It should be recalled that, with closed face tunnelling (EPB or slurry shields),settlement is well controlled and volume loss VL is only < 0.5% in sands and VL = 1% -2% in soft clays. The tunnel at the BEG project Lot H3-4 will be bored by slurry TBMin stratified soils ranging from silt-sand to sand and sand-gravel. Therefore, assuming a

practically maximum volume loss of 2.0 % is reasonable.

Moreover, the theoretical volume loss due to overcut is 5.62 % corresponding with themaximum surface settlement of 38 mm (if K = 0.338 is taken), or 51 mm (if K = 0.25is assumed). If the tunnelling crews carefully control the backfill grouting work at theshield tail to achieve a volume loss less than 2 %, then settlement can be reduced

further.

6.3 Finite Element Modelling

6.3.1 Introduction

New and O'Reilly (1991) already commented that: "Desktop computers can quickly

provide detailed predictions of ground movements due to the most complexunderground excavations. (But) considerable care must be taken in the application of



150

these models and their apparent numerical precision should never be confused for accuracy in the field. The complex interaction of ground conditions and tunnellingmethod demands that engineering judgement and experience will always be required todetermine the appropriate data input to the models and to evaluate the predictions

provided".

In practice, numerical analysis technique must include credible representation of thetunnelling process, in particular the volume loss occurring, including:

• gap between lining and excavated surface;

• internal forces progressively reduced;

• excavated material with reduced strength and deformation properties.

It must also use an appropriate constitutive model for the soil. Linear elastic soilmodels usually give trough widths that are too wide. The heave of the tunnel invert due

to the stress relief may be encountered, which has a dramatic effect in reducing theresulting settlements. Models based on hardening plasticity involving kinematichardening are appropriate, as they can model small strain behaviour, the effect of stresshistory and cyclic loading (Chiriotti, 2006).

Numerical modelling is often carried out to get back-analysis for experimental data, toverify the input parameters that had been assumed in the planning and design phases of the works.

According to Ercelebi et al (2005), 3D model is preferable because for 2D FE models,it is not so easy to estimate pre-relaxation factors (sometimes called stress reductionfactors), which is fraction of load effecting on tunnels, and purely based on practicalexperience. With the 3D model, estimation of pre-relaxation factor is no longer required when excavation stages can be modelled not only in cross-section but also inthe longitudinal section.

Through oral communication, Prof. Swoboda suggested the author, that to calculate thedisplacement of TBM with a 2D model is not recommended. TBM is a really 3D

problem, but 2D can give good results for the lining forces. On the other hand,Vermeer and Möller (2001, 2003) has proposed a smart use of FEM in tunnelling, inwhich the results from a full 3D analysis can match with that from a 2D analysis, withthe use of a so-called β-value (unloading factor) according to the Load Reduction

Method.In this report, Plaxis code will be used to model and predict the development of surfacesettlements.

6.3.2 FE Analysis by Plaxis 2D Professional

Plaxis 2D program will be used to simulate the volume loss by applying a contractionto the shield tunnel lining (uniform 'shrinkage' of the lining elements in a plane normal

to the tunnelling centreline). This contraction is defined during the creation of thetunnel in the input program. A contraction can be specified here because the Lot H3-4



151

tunnel is a circular tunnel (all sections having the same radius) with a homogeneoustunnel lining.

6.3.2.1 Geometry

Geometry

Since the situation here is more or less symmetric, only one symmetric half (the righthalf) of the cross-section is taken into account in the plane strain model. From thecenter of the tunnel the model extends for 40 m in horizontal direction (Figure 106).

The 15-node element is adopted for this analysis. Beam elements are used in Plaxissoftware to model the bending of tunnel lining. The behaviour of these beam elementsis defined using a flexural rigidity, a normal stiffness and an ultimate bending moment.

A plastic hinge may develop for elastoplastic beams, as soon as the ultimate moment ismobilized.

Interfaces are joint elements which are needed for calculations involving soil-structureinteraction. They are used to simulate the thin zone of intensely shearing material atthe contact of tunnel lining.

Figure 106: Geometry of model, right half of the cross-section



152

Material Properties

The depth-dependent moduli of elasticity of soil layers GA_T1, GA_T2 and GA_T3are calculated by the formula f(z) = 0.1 v (0.13 z)w [MN/m2] with v = 373 and w =

0,65. Results are given in Appendix 4, together with other parameters needed for thenumerical model. Average moduli of elasticity of these three soil layers are 23.9MN/m2, 42.6 MN/m2, and 63.2 MN/m2, respectively.

Properties of other soil layers GA_T4 and GA_T6 are given in Table 11 of Section

5.1. Two cases will be tested: wet density, and dry density.

Properties of the precast concrete segments lining are given in Table 17.

Table 17: Material properties of support system

ParametersName/

SymbolValue Unit Formula

Type of behaviour Material type Elastic -

Thickness tc 0.5 m

Area of the cross section A 0.5 m2

Inertia of cross section I 0.0104 m4

Specific weight of concrete

γc 25 T/m3

Specific soil weight γs 20 T/m3

Young's modulus E 37,000,000.00 kPa (37 kN/mm2)

Axial/Normal stiffness EA 18,500,000.00 kN/m

Flexural rigidity (bendingstiffness)

EI 385,416.67 kNm2/m

Equivalent beamthickness d 0.5 m

Equivalent beam weight w 7.5 kN/m/m

Poisson's ratio ν 0.2 -

Maximum moment M p N/A kNm/m(1x10

5units by

default)

Maximum axial force N p N/A kN/m(4.33x106 units bydefault)

3.1

12ct I =

12eq

EI

d EA=

. .2c

c c s

t w t γ γ = −



153

2D mesh generation

The 15-node element is used as the basic element type. The global coarseness will bevaried from coarse to very fine, i.e. from around 500 to 1000 elements for the right half of the given cross section.

Initial conditions

Before the generation of the initial stresses the tunnel lining is to be deactivated. Theinitial stress generation ( K 0-procedure) can be used to generate the initial effectivestresses with the appropriate values of K 0.

The initial stresses in a soil body are influenced by the weight of the material and thehistory of its formation. This stress state is usually characterised by an initial verticalstress σv,0 which is related by the coefficient of lateral earth pressure K 0 (σh,0 = K 0.σv,0).

In reality, the coefficient, K 0, represents the ratio of the horizontal and verticaleffective stresses:

'

0 ' xx

yy

K σ

σ =

In practice, the default K 0-value is based on Jaky (1944) formula (K 0 = 1 - sinϕ) as anempirical expression for a normally consolidated soil.

In PLAXIS initial stresses may be generated by specifying K 0 or by using Gravity

loading . The K 0-procedure should be used in cases with a horizontal surface and with

any soil layers and phreatic lines parallel to the surface. For all other cases Gravityloading shall be used.

Very low or very high K 0-values may cause initial plasticity. Using K 0-values whichdiffer substantially from unity may sometimes lead to an initial stress state whichviolates Coulomb's failure criterion.

6.3.2.2 Calculations

The construction of the tunnel is stimulated by a staged construction calculation inwhich the tunnel lining is activated and the soil clusters inside the tunnel aredeactivated. Deactivating the soil inside the tunnel only affects the soil stiffness andstrength and the effective stresses. Following are the calculation steps in Plaxis.

The first calculation phase is a plasticity calculation, applying load advancementultimate level. For the loading input, Staged construction is selected. Within the stagedconstruction mode, activate the tunnel lining and deactivate the two soil clusters insidethe tunnel.

In addition to the installation of the tunnel lining, the excavation of the soil and the de-

watering of the tunnel, the volume loss is simulated by applying a contraction to theshield tunnel lining.



154

The Contraction parameter is defined as the reduction of the tunnel area as a percentage of the original tunnel area. Activation of the contraction procedure resultsin a homogeneous 'shrinkage' of the tunnel lining, which reduces the cross section areaof the tunnel.

In order to activate this contraction, the procedure is:• Select a plastic calculation, load advancement ultimate level and select Total

multipliers as loading input.

• Enter a contraction value of 0.5 ÷ 2.5 for the parameter Σ McontrA. This is themultiplier that controls the contraction of the tunnel referred to as 'A' in thegeometry model.

• Select some characteristic points for load-displacement curves (for example thecorner point at the ground surface above the tunnel, and the point on top of lining).

• Start the calculations.

It is noted that, the contraction of the shield tunnel lining by itself does not introduceforces in the tunnel lining. Eventual changes in lining forces as a result of thecontraction procedure are due to stress redistributions in the surrounding soil or tochanging external forces.

Through many runs with variations of lining thickness (from 30 to 60 cm), meshcoarseness (500 ÷ 1000), and contraction value (0.5 ÷ 2.5), it is observed that the soil

body collapses at different contraction values, and settlements as well as liningmember forces also fluctuate accordingly.

Finally, plane strain computation is made for the actual structure as follows:

- lining thickness of = 50 cm;

- number of elements = 959;

- number of nodes = 7868;

- number of stress points = 11508

Computed results:

- contraction converged (soil body collapses) at 1.3 % for the case of using wet density of soil; extreme total displacement is 82 mm (Figure107)

- contraction converged at 1.01 % if the dry density of soil is used;extreme total displacement is 64 mm (Figure 108)



155

Figure 107: Deformed mesh (displacement scaled up 50 times)

Figure 108: Shadings of vertical displacements



156

It can be seen from Figure 109 that, the vertical displacements on the surface (52 mm)are smaller that that on the tunnel crown (64 mm). But the trough width at the tunnelcrown level is narrower and steeper than at ground level.

a)

b)

Figure 109: Settlement troughs on the surface a) and at crown level b)

Figure 110 shows the development of settlements of four different points in the groundwhen the contraction is increased. When the contraction reaches 1.01 %, soil bodycollapses, the settlement of Point A at the tunnel bottom attains 10 mm, the settlementof Point B on top of tunnel (crown) is 64 mm, the settlement of Point C on the side of tunnel (haunch) is 40 mm, and the settlement of Point D near the ground surface is 52mm.



157

Figure 110: Development of vertical displacements of different points

In Table 18 and 19 are compared the settlements obtained from the empirical analysisand from 2D modelling, at the same values of volume loss of 1.3 %, and 1.0 %,respectively. The settlement given by 2D modelling is greater than that of empiricalformula.

Table 18: Comparison of settlement results between empirical methods and 2D

analysis, VL = 1.3 % (using wet density of soil)

O'Reilly & New(1982)/Mair et al(1996) formula

2D Plaxismodelling

Max settlement (mm) 9 82

Volume loss (%) 1.30 1.3

(k=0.338)



158

Table 19: Comparison of settlement results between empirical methods and 2Danalysis, VL = 1.0 % (using dry density of soil)

Mair et al (1996)formula

2D Plaxismodelling

Max settlement (mm) 7 64Volume loss (%) 1.00 1.01

(k=0.338)

Lining forces

Normal force and bending moment in tunnel lining are shown in Figure 111. Extremeaxial force is -947.08 kN/m, extreme shear force is 110.80 kN/m, and extreme bendingmoment is -329.78 kN/m. These member forces can be used to design the

reinforcement for the lining.

a) Axial forces b) Shear forces



159

c)

-2.50 0.00 2.50 5.00 7.50 10.00 12.50 15.00 17.50

-5.00

-2.50

0.00

2.50

5.00

7.50

Bending moment

Extreme bending moment -329.78 kNm/m

Figure 111: Axial forces a), shear forces b), and ending moment c) in the lining

Stress paths

A stress path represents the development of the stress state at a local point of thegeometry. The visualization of stress paths provides a valuable insight into local soil

behaviour. The stress paths of four points are shown in Figure 112: Point F at thetunnel bottom, Point G on top of tunnel (crown), Point H on the side of tunnel(haunch), and Point I near the ground surface.

Figure 112: Stress paths of different points



160

6.3.3 Face Stability by Plaxis 3D Tunnel

Tunnel heading stability, ground deformation/surface settlements, and loads on liningare the three main focuses of tunnel analyses (Vermeer, 2001).

The shield tunnel construction can be modelled as a stepwise process. During theerection of the tunnel lining the tunnel boring machine (TBM) remains stationary.Once a tunnel lining ring has been fully erected, excavation is resumed, until enoughsoil has been excavated to erect the next lining ring. As a result, the construction

process can be divided in construction stages (slices) with a length approximatelyequal to a tunnel ring.

The excavation process in each staged construction phase is: the support pressure at thetunnel face needed to prevent active failure at the face, the conical shape of the TBMshield, the excavation of the soil and pore water within the TBM, the installation of thetunnel lining and the grouting of the gap between the soil and the newly installed lining(Figure 113).

Figure 113: Construction stages of a shield tunnel

Although runs of the 3D phased excavation of a shield tunnel with limited excavation

steps can only be completed in approximately several hours, it is worth performing,considering the value of the information it is able to provide and the complexity of themodel.

However, in this subsection only the stability of the tunnel face will be investigated.Only the TBM is included in the model and the tunnel lining is not modelled. The

purpose is to search for the minimum face pressure that is required to keep the tunnelheading stable by lowering the original face pressure until collapse occurs.

final lining groutpressure

TBM

face pressure

contraction of shield



161

6.3.3.1 Geometry

In the model, again only one symmetric half is included, but it is the left half in thiscase. The model is 40.0 m wide, it extends 55.0 m in the z-direction and it is 52.0 mdeep. With these dimensions (over three times of tunnel diameter in three directions),

the model is sufficiently large to allow for any possible collapse mechanism to developand to avoid any influence from the model boundaries.

The tunnel excavation process is simulated in one excavation stage. The interaction between the TBM and the soil is modelled by means of an interface. The tunnel face pressure is modelled by means of a z-load, which is applied in the excavation stage.

Boundary conditions

Standard fixities function of the program will generate full fixities at the bottom,

vertical rollers at the vertical sides and rotation fixities at the ends of the tunnel. Thegeometry model is shown in Figure 114.

Figure 114: Geometry model in the Input window

Material properties

The material properties of the soil clusters and other geometry objects are entered indata sets. Interface properties are included in the data sets for soil.

In addition to the material data sets for soil and interfaces, a data set of the plate type is

created for the TBM, with the properties as given in Table 20.



162

Table 20: Material properties of the TBM

TBM Parameters Name Value Unit

Type of behaviour Material type Elastic -

Axial/Normal stiffness EA 12,600,000 kN/mFlexural rigidity(bending stiffness)

EI 85,000 kNm2/m

Equivalent thickness d 0.285 m

Weight w 50.77 kN/m/m

Poisson's ratio ν 0.00 -

Mesh generation

The 2D mesh should be made fully satisfactory before proceeding to the 3D meshextension. The basic volume elements of the 3D finite element mesh are the 15-nodewedge elements. In addition to the basic volume elements, there are special elementsfor structural behaviour (plates, geogrids and anchors). PLAXIS allows for a fullyautomatic generation of 2D finite element meshes and a semi-automatic generation of 3D meshes.

The standard very coarse mesh is used first. 2D mesh is shown in Figure 116. Model: plane strain; Elements: 6-noded; number of elements: 68; number of nodes: 170;number of stress points: 204.

Figure 115: 2D finite element mesh



163

3D mesh is shown in Figure 116. Model: 3D parallel planes; Elements: 15-nodedwedge; number of elements: 612; number of nodes: 2168; number of stress points:3672.

Figure 116: 3D finite element mesh

Initial conditions

The initial conditions of the current project require the generation of water pressuresand the generation of initial stresses. The generation of water pressures (i.e. pore

pressures and water pressures on external boundaries) is based on the input of phreaticlevels of 17.5 m (Figure 117). The initial stresses are generated by means of the K 0-

procedure (Figure 118).



164

Figure 117: Active pore pressures (initial)

Figure 118: Effective mean stresses (initial)

6.3.3.2 Calculations

We concentrate on the tunnel heading stability and consider that the TBM has already

advanced its own length (11.35 m) into the soil. The first construction phase willconsist of the excavation of the soil to allow the installation of the TBM, the



165

application of the TBM itself, the lowering of the water level in the TBM, theapplication of the tunnel face pressure and the application of contraction to simulatethe fact that the TBM is conical towards its tail (0.5 %). The adapted material sets(with reduced interface friction and adhesion) are assigned to the first slice in whichthe tunnel is excavated.

The tunnel face pressure needs to be applied to the face of the TBM, and is maintained by a fluid (bentonite) with a unit weight of 14.0 kN/m3. The tunnel face pressure is120.0 kN/m2 in the negative z-direction at the top of the tunnel (+6.49 m) and 302.0kN/m2 at the bottom (-6.49 m). The pressure gradient is 14.0 kN/m2/m. A referenceordinate yref of +6.49 m (corresponding to the top of the tunnel), a reference pressure

pref of -120.0 kN/m2 and a pressure increment pinc of -14.0 kN/m2/m are introduced.

A contraction value will be introduced to model a shortening of the tunnel shell andthus a reduction of the tunnel radius during the calculation, i.e., to simulate the soilvolume loss around the tunnel due to overcutting, conicity of the TBM, or any other

cause. The value of contraction defines the cross section area reduction as a percentageof the whole tunnel cross section area. Here, the tail of the TBM will be given acontraction of 0.5% to simulate the conicity of the TBM.

Inside of the tunnel will be set dry in the first excavation phase. Active pore pressuresare given in Figure 119.

Figure 119: Active pore pressures in the first excavation phase



166

The minimum required tunnel face pressure can be found by reducing the tunnel face pressure until the tunnel heading collapses. Calculation type is 3D plastic. Calculation phase 2 starts from Phase 1. All loads defined as load system A (in this case only theZ-Load representing the tunnel face pressure), will gradually be reduced to 0.

Several nodes and stress points will be selected for a later generation of load-displacement curves and stress and strain diagrams. On the TBM workface plane arechosen:

• Nodes for load-displacement curves: Point A is at the bottom, point B at tunnelhaunch, point C on top of tunnel and point D at the ground surface right abovethe tunnel.

• Stress points for Stress/Strain curves: Point E is at the bottom, point F at tunnelhaunch, point G on top of tunnel and point H near the ground surface rightabove the tunnel.

The first calculation phase should successfully finish (Figure 120). It can be seen thatthe original face pressure is sufficiently high to keep the tunnel face stable. Thedisplacements at the tunnel face are very small. The largest deformations 30 mm occur above the tail of the TBM. This is due to the applied contraction.

Figure 120: Deformed mesh at the end of phase 1

The total and incremental values of the realised contraction can be seen from Figure121. The total realised contraction of 0.52 % almost corresponds to the input value of

0.5 %.



167

Figure 121: Realized value of contraction, at Front Plane (left) and Face Plane (right)

The second calculation phase should not successfully finish, because the Prescribed

ultimate state not reached , and Soil body collapses (Figure 122).

Figure 122: Finish of the calculation phases



168

The Multipliers parameter Σ- MloadA has reached a value of 0.9058, so the minimumtunnel face pressure required to prevent failure is 0.9058 x 120.0 = 108.7 kN/m2 at thetop and 0.9058 x 302.0 = 273.3 kN/m2 at the bottom of the tunnel. This gives an idea

about the safety of the tunnel heading against active failure.The total displacement is 31 mm.

Safety Analysis

It is important to consider not only the final stability, but also the stability duringconstruction. The stability against failure can be defined by means of a safety factor. Asafety factor can be defined as the ratio of the available shear strength to the computedminimum strength required for equilibrium:

available

needed for equilibrium

S Safety factor S

=

By introducing the standard Coulomb condition, the safety factor is obtained as:

tan

tann

r n r

cSafety factor

c

σ ϕ

σ ϕ

+=

+

Where c and ϕ are the input strength parameters and σn is the actual normal stresscomponent. The parameters cr and ϕr are reduced strength parameters that are justlarge enough to maintain equilibrium. The principle described above is the basis of the

method of Phi-c reduction that can be used in PLAXIS to calculate a global safetyfactor. In this approach the cohesion and the tangent of the friction angle are reducedin the same proportion:

tan

tanr r

c sf

c

ϕ

ϕ = = Σ

The reduction of strength parameters is controlled by the total multiplier ΣMsf. This parameter is increased in a step-by-step procedure until failure occurs (calculation phase 3). The safety factor is then defined as the value of ΣMsf at failure.

To calculate the global safety factor for the situation of the original face pressure, thefirst increment of the multiplier for strength reduction ( Msf ) is preset to 0.1.

The deformations obtained for the second and the third phase will be shown below for comparison. Both the second and the third phase represent a collapse situation. Thesecond phase (face pressure reduction) shows the soil locally moving inwards (Fig.123), whereas the third phase (phi-c reduction) shows a chimney-like failuremechanism reaching to the ground level (Fig. 124).



169

Figure 123: Displacement increments at the end of Phase 2 (face pressure reduction)

Figure 124: Displacement increments at the end of Phase 3 (Phi-c reduction)

The development of the Σ-MloadA multiplier and the development of the Σ-Msf multiplier can be viewed in Figure 125 and Figure 126.

Figure 125 shows that, in the second phase, ΣMloadA reaches a value of 0.9058, atwhich large inward movements of the tunnel face occur.

Figure 126 shows that, in the third phase, ΣMsf (may be regarded as a global safetyfactor) reaches a value of 2.027, at which large inward movements of the tunnel face

occur.



170

However, in this type of application the procedure of phi-c reduction does not give arealistic safety factor. This is because the problem is very much dominated by thetunnel face pressure, which is not reduced in the phi-c reduction procedure. Themethod of phi-c reduction is much more applicable for embankment or slope stability

problems, and does give a realistic safety factor in such cases.

Figure 125: Development of Sum-MloadA as a function of the displacements



171

Figure 126: Development of Sum-Msf as a function of the displacements

Concluding notes

It should be noted, that this type of tunnel face stability can only be justified if thematerial properties of the TBM are correctly given by the machine manufacturer.

In order to avoid mistakes in the modelling of face stability as well as phasedexcavation of a shield tunnel with the use of Plaxis 3D Tunnel program, it is desirableto:

• prescribe enough displacements on active mesh;

• avoid very slender elements;

• refine around tunnel(s); and

• reduce stiffness differences.

6.4 Summary

Surface settlements were predicted for the tunnel to be excavated in the section of Km33+480 to 33+800 of BEG project line using both empirical and numerical prediction

methods.



172

With the analytical methods, different empirical formulae result in differentsettlements with the same volume loss.

2D analysis presented the bigger values of settlement with the same volume loss.However, these may give some useful indications before construction begins.

Although 3D analysis of face stability gave out a total settlement of 31 mm, it isunsuitable to make a comparison with the aforementioned results, since it did notaccount for staged excavation and grouting pressure as well as lining installation.

Limitations of the analytical/empirical methods are that, they are specific to soil typeand unable to account for soil-lining interaction. Empirical methods may be useless for the complex structural configurations. Actual construction works commonly comprisea variety of intersecting excavations where tunnels may change diameter (e.g. stations)and where cross connecting adits occur. It is often difficult to readily calculate

important 3D ground movements at these complex locations.Limitations of the numerical method are that, when modelling the shield tunnelling

problem in 2D, the extrusion of the face may hardly be modelled directly, and the usersmay have to rely on some "tricks" during generating the mesh and base onapproximations of the lining behaviour. Phased construction also has never beenexactly modelled. For 2D FE models, it is not so easy to estimate pre-relaxation

factors (sometimes called stress reduction factors), which is fraction of load effectingon tunnels, and purely based on practical experience.

The Plaxis software's assumption that the contraction of the tunnel lining (applied tosimulate the ground loss) by itself does not introduce forces in the lining is somewhatartificial. It could be interesting if some correlation is made to the load reductionmethod and the stiffness reduction method used for taking into account 3D effects in2D analyses (Schweiger et al, 1997). Also, one can have recourse to the explanation of Augarde et al, in that the hoop shrinkage is achieved by the application of a suitable setof radial forces within the tunnel liner. The process leads to fictitious stresses withinthe liner, but the liner is elastic and so this does not affect the way in which the groundand the liner interact.

The two methods can be used together for a given project to cross-check one another.The FEM is a strong tool but it still depends on the qualification of the users, not

including specific adaptations or approximations. And it is vital that the output fromthe analysis is checked carefully. It is hoped that the future developments andenhancement of the presently available specialist codes will help to address theoutstanding problems.



173

Chapter 7

7. Conclusions and Future Work

Conclusions

In preparation of this final project, the author has investigated both theoretical and practical aspects of interactions within TBM excavations as well as interfaces between

TBM and lining. The theoretical part attempted to make clear a number of critical points that have to be paid due attention in the design and construction of tunnels. Numeral calculations have been conducted to illustrate the theoretical part. In reviewof the report, a few points are recapped below.

• A rather comprehensive investigation has been performed on the interface between TBM and lining, from a practical engineering standpoint, which helpsto make clear many outstanding issues relating to TBM tunnels design,construction and project management.

• High performance TBMs are essential for the successful construction of tunnel

projects. The TBMs will be purpose built machines using proven “state of theart” technology and designed specifically for the project to a minimumspecification to ensure their reliability in terms of performance and settlementcontrol. They should be designed to cater for the range of ground conditionsanticipated.

• Given the advances in tunnelling technology today, tunnels can be excavated invirtually all types of soil and environment, but there are still numerousunknown parameters. One of the most important is the knowledge of the groundthrough which the tunnel will be routed. Therefore, geotechnical design should

be based on adequate geotechnical investigation, then data evaluation provided,

and monitoring program elaborated.

• Risk management procedures should be provided for to cover all the possiblerisks; prepare measures to deal with that risks including corresponding costestimate. Risks have to be considered from the first steps of the tunnel project,through installation process to its operation. Budget for risk managementshould be allocated and defined in tender documents and contract requirements.

• For the purpose of understanding and managing the surface settlement, the problem of face stability has been reviewed. Countermeasures to ground failuredue to urban tunnelling are also given, with the particular use of grouted bodies.

A case history of Metro Torino has been presented to show the application of those grout-consolidated slabs.



174

• Ground settlements caused by shielded tunnelling operations have beenexamined with both analytical and numerical approaches, then resultscompared. Face heading stability has also been analyzed by 3D numerical tool.

Numerous parameter studies have helped the author to gain a critical view onthe use of the available approaches. Semi-empirical methods must be applied

with caution, and finite element analysis with geomechanical software must beused toward an effective way.

Recommendations for future studies

• Simulation of the subsidence induced by the excavation of single, twin tunnelsor even more complex configurations, taking into account the presence of surface structures or structures within the zone of influence of the tunnels. A

clear presentation of the effects of tunnelling on overlying structures isobviously the next step to pursue.

• Design of segmental concrete linings for tunnels in soft soils using 3-Dnumerical modelling, with the reasonable consideration of soil-structure(ground-lining) interaction. It would be useful if different commercial packagessuch as PLAXIS, FLAC, Phase2, etc. are used together with analytical methodsto compare and validate the respective results.

• Otherwise, study in the feasible alternatives for the realization of deep and longtunnels coming from various markets, such as the railway link beneath the

Strait of Gibraltar, which have an essential need for implementation of flexibleresponses due to observations and definitely involves the discussed criticalinterfaces, both contractually and technically.



List of Acronyms

ENGLISH

ABI : Association of British Insurers

ACI : American Concrete Institute

ANN : Artificial Neural Networks

AR : Advance Rate

BOQ : Bill Of Quantities

BS : British Standards

BTS : British Tunnelling Society

CBP : Controlled Boring Process

CEVP : Cost Estimate Validation Process

CHD : Cutter Head Drive

CLI : Cutter Life Index

COE : U.S. Army Corps of Engineers

CSI : Computers and Structures, Inc.

D&B : Drill & Blast / Drilling and Blasting method

DAT : Decision Aids in Tunnelling

DRB : Disputes Review Board DSC : Differing Site Condition

DSU : Double Shield Universal

DTA : Designed Tunnel Axis

ELS : Electronic Laser System

EPB : Earth Pressure Balance

EPBM/EPBS : Earth Pressure Balance Machine/ShieldEPDM : Ethylen-Propylen-Dien Material

EPFL : Ecole Politechnique Fédérale de Lausanne

EU : European Union

FEM : Finite Element Method

FER : Foam Expansion Ratio

FIR : Foam Injection Ratio/Rate

FLAC: Fast Lagrangian Analysis of Continua

GBR : Geotechnical Baseline Report



GIS : Geographical Information System

GTS : Gyro Tunnelling System

HM : Hand Mining

HS : Hardening Soil model

ICE : Institution of Civil Engineers

IMIA : International Association of Engineering Insurers

ITA-AITES : International Tunnelling Association - AssociationInternationale des Travaux en Souterrain

ITIG : International Tunnelling Insurance Group

JSCE : Japan Society of Civil Engineers

MFS : Multi-circular Face Shield

MIT : Massachusetts Institute of Technology

MT : Mechanized Tunnelling

NATM : New Austrian Tunnelling Method

NMT : Norwegian Method of Tunnelling

PLAXIS : PLasticity AXISymmetry

PR : Penetration Rate

QA/QC : Quality Assurance/Quality Control

RMP : Risk Management Plan

RPM : Revolutions Per Minute

RQD : Rock Quality Designation

SCL : Sprayed Concrete Lining

SFRC : Steel Fiber Reinforced Concrete

SM : Shield Machine

SRF : Stress Reduction Factor

SS : Soft Soil modelTBM : Tunnel Boring Machine

TEN : Trans-European Transport Network

UCS : Uniaxial Compressive Strength

VAL : Automated Light Vehicle

WSDOT : Washington Department of Transportation



FRENCH

AFTES : Association Française des Travaux en Souterrain (French

Association of Tunnels and Underground Space)

FIDIC : Fédération Internationale des Ingéniers-Conseils (InternationalFederation of Consulting Engineers)

GERMAN

AVN : Automatischer Vortrieb Naß (Automatic/remote controlled

Wet/slurry Driving/tunnelling machine)

BEG : Brenner Eisenbahn GmbH (Brenner Railway Ltd.)

DAUB

: Deutscher Ausschuß für unterirdisches Bauen (German

Committee for Underground Construction)

DIN: Deutsches Institut für Normung e.V. (German Institute for

Standardadization, registered society)

ÖBB : Österreichisches Bundesbahn (Austrian Federal Railway)

ÖNORM :Österreichisches Normungsinstitut (Austrian Standards

Institute)

ITALIANADECO-RS : Analisi delle Deformazioni Controllate nelle Rocce e nei Suoli

(Analysis of Controlled Deformation in Rocks and Soils)COREP : Consorzio per la Ricerca a l’Educazione Permanente

(Consortium for the Research and Permanent Education)

GTT : Gruppo Torinese Trasporti (Turin Transportation Group)

RFI : Rete Ferroviaria Italiana SpA (Italian Railway Network; or

National Railway Infrastructure Administration)

SELI

: Società Esecuzione Lavori Idraulici S.p.A. (Hydraulic Works

Construction Company)

SIG : Società Italiana Gallerie (Italian Tunnelling Society)

S.p.A : Società per Azioni (Joint stock company)

RUSSIAN

СНиП (SNiP) : Строительные Нормы и Правила (Construction standardsand regulations)



References

[1] AFTES (1995) Settlements induced by tunnelling . Association Française des

Travaux en Souterrain (The French Association of Tunnels and UndergroundSpace).

[2] AFTES (1999). Recommendation for the design, sizing and construction of

precast concrete segments installed at the rear of a tunnel boring machine(TBM). The French Association of Tunnels and Underground Space.

[3] AFTES 2000. New recommendations on Choosing mechanized tunnelling techniques. French Tunnelling and Underground Engineering Association.

[4] Anagnostou G., Kovari K. (1994). The Face Stability of Slurry-shield-driven

Tunnels. Tunnelling and Underground Space Technology, Volume 9, Issue 2,

165-174.[5] Andreossi E. 2001. Costs - The Insurers Point of View. International Centre for

Geotechnics and Underground Construction (CUC). BEMA, Switzerland.

[6] Arrigoni G.A. 2006. Project management - Contractual and legislative aspects.Lecture at Master Course in Tunnelling and TBMs, Edition V 2005-2006,Politecnico di Torino, Italia.

[7] Assis A. P. 2006 - Examples of Underground Excavations in Rock (Part 1);Gibraltar Strait Crossing (Part 4). Lecture series at Master Course in Tunnellingand TBMs, Edition V 2005-2006, Politecnico di Torino, Italia.

[8] Augarde C.E., Burd H.J. and Houlsby G.T. Some experiences of modelling tunnelling in soft ground using three-dimensional finite elements. 4th EuropeanConference on Numerical Methods in Geotechnical Engineering.

[9] Barla G. 1998. Tunnelling under squeezing rock conditions. Department of Structural and Geotechnical Engineering, Politecnico di Torino, Italia.

[10] Barla G. & Pelizza S. 2000. TBM tunnelling in difficult ground conditions. Proc.GeoEng2000, Melbourne.

[11] Barton N., 1999b: TBM performance estimation in rock using QTBM . Tunnels &Tunnelling, September 1999, pp. 30-34.

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Appendix 1A

EOLE Lot 35B Project

Paris / France

Years of construction: 1992 - 1995.

The subway line (EOLE) is running 35 m deep under the city center of Paris.

Job description

Detail design and construction consultancy for an innerurban railway tunnel which

connects the two stations of “St. Lazare - Condorcet” and “Nord - Est”.

The tunnel has a length of 2 x 1.670 m, an inner diameter of 6.4 m, a segment thickness

of 35 cm and an overburden between 22 m and 28 m.

Services provided by D2-Consult for DG Construction Paris

- Detailed design of tunnel lining

- Geometry of regular cross section

- Alignment study by ring rotations

- Segment installation sequences

- Joint Configurations

- Segment dimension - "Mould" drawings

- Segment reinforcement

- Structural analysis

- Thrust jacking loads

- Trailer loads

- Secondary grouting

- Eccentricity during segment installation

- Construction consultancy on site

- Analysis of segment quality

- Twisting of segments

- Offsets in circumferential joints

- Observation of segment installation and recommendations

Back analysis of the segmental ring elements of one pass lining for 2 TBM connecting

tunnels, 1.700 m length and 6.4 m inner diameter. Tunnels are excavated 30 m beneath

the surface. Transition structure is located on the level of Saint-Ouen limestone as well aswater saturated Beauchamp sands. Connecting tunnels are crossing successive horizons

of marl, gravel and heavy limestone beneath the ground water table.



EOLE LOT 35 B / FRANCE

INNERURBAN RAILWAY TUNNEL

LOCATION

INSTALLATION OF A RHOMBOIDAL SEGMENT

TBM – POLYSHIELD TBM TUNNEL – CROSS SECTION

PARIS

PROJECT DESCRIPTION

DETAIL DESIGN AND CONSTRUCTION CONSULTANCY FOR AN

INNERURBAN RAILWAY TUNNEL WHICH CONNECTS THE TWO

STATIONS OF ”ST.L AZARE - CONDORCET“ AND ”NORD - EST”.

THE TUNNEL HAS A LENGTH OF 2 X1.670M, AN INNER DIAMETER

OF 6,4 M, A SEGMENT THICKNESS OF 35CM AND AN

OVERBURDEN BETWEEN 22M AND 28M.

SERVICES PROVIDED

- DETAILED DESIGN OF TUNNEL LINING

- GEOMETRY FO REGULAR CROSS SECTION

- A LIGNMENT STUDY BY RING ROTATIONS

- SEGMENT INSTALLATION SEQUENCES

- JOINT CONFIGURATIONS

- SEGMENT DIMENSION – ”MOULD” DRAWINGS

- SEGMENT REINFORCEMENT

- STRUCTURAL ANALYSIS

- THRUST JACKING LOADS

- TRAILER LOADS

- SECONDARY GROUTING

- ECCENTRICITY DURING SEGMENT INSTALLATION

- CONSTRUCTION CONSULTANCY ON SITE

- A NALYSIS OF SEGMENT QUALITY

- T WISTING OF SEGMENTS

- OFFSETS IN CIRCUMFERENTIAL JOINTS

- OBSERVATION OF SEGMENT INSTALLATION AND

RECOMMENDATIONS

PERIOD OF WORK : 1992 - 1997

V OLUME OF WORK : 206.150 EURO

O WNER: SNCF

Appendix 1B



Boston Outfall Tunnel Project

Boston / USA

Owner Water Resources Authority Massachusetts

Client Sehulster Tunnels Inc. Concrete Systems Inc. JV

Contact: Mr. Joseph P. Sehulster, Tel. +1 603 8894-163

Project The tunnel underneath Boston Harbour and brings cleaned waste water fromthe Deer Island treatment plant over discharger pipes to the open sea. The 55outfall tunnel diffusers, located at regular intervals over the final 2km, weredrilled from the sea-bed and connections made by probe drilling from thetunnel.

The main tunnel was driven by TBM through hard rock Cambridge Argillite andlined with pre-cast concrete segments

Project Details Inner diameter 7.4 m

Tunnel length 14 km

Overburden 45 m

Segment thickness 25 cm

Services • Detailed lining design („Conex System“)

• Engineering for in-situ testing

• Construction consultancy

Period of Work 10/1990 – 12/1995

Volume of Work EUR 223,000

TBM Tunnel – segment supply

Appendix 2A



BOSTON EFFLUENT OUTFALL TUNNEL / USA

DETAILED DESIGN OF LINING SEGMENTS

LOCATION

CROSS SECTION LONGITUDINAL SECTION

SEGMENT SUPPLY SEGMENT WITH TIMBER DOWELS IN RING JOINT

PROJECT DESCRIPTION

TBM DRIVEN AND SEGMENTAL LINED WATER TUNNEL IN ARGELITIC

ROCK UNDERNEATH BOSTON H ARBOUR.

INNER DIAMETER 7,40 M

LENGTH 14 KM

O VERBURDEN 45 M

SEGMENT THICKNESS 25 CM

SERVICES PROVIDED

- DETAILED LINING DESIGN CONEX S YSTEM

- ENGINEERING FOR IN-SITU TESTING

- CONSTRUCTION CONSULTANCY

PERIOD OF WORK : 10/1990 – 12/1995

V OLUME OF WORK : 223,000 EURO

BOSTON

O WNER: W ATER RESOURCES A UTHORITY M ASSACHUSETTS

Appendix 2B



Appendix 3

Type of PressureForce per

Ring

No. of

Shoes

Force per

Thrust

Shoe

Thrust

Shoe Area

Pressure

on Thrust

Shoe

Conc

Facto

Com

50/60

[kg/c

[-] [t] [-] [t] [cm2] [kg/cm

2]

Installed advance pressure

(max. machine)10344.6 21 492.60 95 x 17 1615 305.0

Excavation in Sand-Gravel

(max. force)9051.5 21 431.02 95 x 17 1615 266.9

Excavation in Coarse

Gravel (approx. 60% of

max. force)

5430.9 21 258.61 95 x 17 1615 160.1

Excavation in Fine Gravel

(approx. 33% of max.

force)

2987.0 21 142.24 95 x 17 1615 88.1

Average Installation (15

ton/dowel) 315 21 15.00 95 x 17 1615 9.3

Thrust Shoe

Dimentions

[cm]

JACKING THRUST PRESSURE ON LINING, BEG TUNNEL8 Segment Rings (5 rectangular, 2 Trapezoids, 1 Keystone)

Remarks: Thrust shoe dimensions are supposed only as machine has not yet been officially



Appendix 4

BEG LOT H3-4. INPUT PARAMETERS FOR HARDENING SOIL MODEL

"GREEN-FIELD" CROS-SECTION

Soil Layer

Volumetric

weight gamma

γ [kN/m3]

Real depth

[m]

Cohesion c

[kN/m2]

Friction

angle φ

[deg]

Dilactancy

angle ψ

[deg]

Poison's

ratio νur

E-Modul

[MN/m2],

f(z) =

0.1v(0.13z)w

Coefficient of

lateral stress

Ko=1-sinφ

GA_T1 21 21.8 0 37 0.20 0.000 0.398

GA_T1 21 21.3 0 37 0.20 6.311 0.398

GA_T1 21 20.8 0 37 0.20 9.903 0.398

GA_T1 21 20.3 0 37 0.20 12.889 0.398

GA_T1 21 19.8 0 37 0.20 15.540 0.398

GA_T1 21 19.3 0 37 0.20 17.965 0.398

GA_T1 21 18.8 0 37 0.20 20.226 0.398

GA_T1 21 18.3 0 37 0.20 22.357 0.398

GA_T1 21 17.8 0 37 0.20 24.384 0.398

GA_T1 21 17.3 0 37 0.20 26.325 0.398

GA_T1 21 16.8 0 37 0.20 28.190 0.398

GA_T1 21 16.3 0 37 0.20 29.992 0.398

GA_T1 21 15.8 0 37 0.20 31.737 0.398

GA_T1 21 15.3 0 37 0.20 33.432 0.398

GA_T2 21 14.3 0 37 0.20 36.691 0.398

GA_T2 21 13.3 0 37 0.20 39.801 0.398

GA_T2 21 12.3 0 37 0.20 42.785 0.398

GA_T2 21 11.3 0 37 0.20 45.661 0.398

GA_T2 21 10.3 0 37 0.20 48.442 0.398

GA_T2 21 9.3 0 37 0.20 51.140 0.398

GA_T3 21 8.8 0 37 0.20 52.461 0.398

GA_T3 21 8.3 0 37 0.20 53.764 0.398

GA_T3 21 7.8 0 37 0.20 55.050 0.398

GA_T3 21 7.3 0 37 0.20 56.320 0.398

GA_T3 21 5.8 0 37 0.20 60.041 0.398

GA_T3 21 4.3 0 37 0.20 63.642 0.398

GA_T3 21 2.8 0 37 0.20 67.137 0.398

GA_T3 21 1.3 0 37 0.20 70.536 0.398

GA_T3 21 -0.2 0 37 0.20 73.849 0.398

GA_T3 21 -1.2 0 37 0.20 76.014 0.398

GA_T3 21 -2.2 0 37 0.20 78.146 0.398





Curriculum Vitae

Name Nguyen Duc Toan

15.9.1974 Born in Hanoi, Vietnam

June 1991 Graduated from Dan Phuong secondary school, Hanoi, Vietnam

1991-1996 Enrolled at Bridge and Tunnel Engineering Section, Faculty of Engineering, University of Communication and Transport, Hanoi,

Vietnam

June 1996 Bachelor Degree of Civil Engineering from University of Communication and Transport, Vietnam

1996-1998 Employed as an Assistant Bridge Engineer by Taisei-Rotec Joint-

Venture, Hanoi, Vietnam

1998-2000 Enrolled at Pedagogic English Section, Faculty of Continuing

Education, College of Foreign Language - Vietnam National

University, Hanoi

April 2000 Bachelor Degree of Foreign Language from College of ForeignLanguage - Vietnam National University, Hanoi

1998-2001 Employed as a Bridge Engineer by Louis Berger Inc., Hanoi,Vietnam

2001-2004 Employed as a Tunnel Inspector by Transport Engineering Design

Inc. (TEDI), Hanoi, Vietnam

March 2004 Consulting Engineer Certificate (Construction Supervision) byMinistry of Transport of Vietnam

Since 2004 Employed as a Civil Engineer by Institute of Transport Science and

Technology (ITST), Hanoi, Vietnam

Since 2005 Study for Master Degree at University of Technology of Turin, in

partnership with Consortium of Research and Permanent Educationof Turin, Italy

Contact [email protected]; [email protected]



Post Graduate Master Course by Politecnico di Torino (University of Technology)

TUNNELLING AND TUNNEL BORING

MACHINESV EDITION 2005-06

Master endorsed by ITA/AITES

Under the patronage of SIG ITALIAN TUNNELLING SOCIETY