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Spring 2010

Engineering OptionsReport

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Please note:

Further details are provided in the Final Report on SiteSelection Process (doc ref: 7.05) that can be found onthe Thames Tideway Tunnel section of the PlanningInspectorates web site.

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Engineering Options Report

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THAMES TUNNEL

ENGINEERING OPTIONS REPORT

LIST OF CONTENTS

Page Number

1 EXECUTIVE SUMMARY 12 INTRODUCTION 2

2.1 Purpose of report 22.2 Background to project 32.3 Engineering design development 3

3 SYSTEM DESIGN AND ENGINEERING REQUIREMENTS 43.1 System design and engineering assumptions 43.2 Health and safety considerations 43.3 System requirements 43.4 Engineering geology 113.5 Tunnel engineering and construction requirements 143.6 CSO engineering and construction requirements 23

4 ENGINEERING DEVELOPMENT AND COMPARISON OF OPTIONS 274.1 Introduction 274.2 Main tunnel engineering options preparation 274.3 Main tunnel engineering options assessment 434.4 CSO engineering options 49

5 CONCLUSIONS AND RECOMMENDATIONS 55APPENDICES

The following appendices can be found in the accompanying document Engineering OptionsReport Appendices (100-RG-ENG-00000-000009):

APPENDIX A ASSUMPTIONS REGISTER

APPENDIX B DRAWINGS

APPENDIX C TIME CHAINAGE

APPENDIX D GEOLOGY

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LIST OF FIGURES

Page Number

Figure 3.1 General layout of the three Thames Tunnel routes being considered ............................ 8Figure 3.2 Thames Tunnel CSO connection main system elements............................................. 9

Figure 4.1 Main tunnel shaft zones ................................................................................................. 29Figure 4.2 Key for matrix of possible drives .................................................................................... 33Figure 4.3 Main tunnel shaft site types ........................................................................................... 37Figure 4.4 Drive option example ..................................................................................................... 38Figure 4.5 Type A CSO connection ................................................................................................ 49Figure 4.6 Type B CSO connection ................................................................................................ 50Figure 4.7 Type C CSO connection ................................................................................................ 51Figure 4.8 Type D CSO connection ................................................................................................ 52Figure 4.9 Type E CSO connection ................................................................................................ 53

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LIST OF TABLES

Page Number

Table 3.1 Details of combined sewer outfall ..................................................................................... 5Table 3.2 Geology of London Basin ................................................................................................ 12

Table 3.3 Chalk aquifer groundwater levels 2008 and imposed pressure at tunnel invert (east ofShad) ................................................................................................................................................ 14Table 4.1 Grouping of main tunnel drive sites ................................................................................ 29Table 4.2 Western End drive options consideration of practical drive lengths ............................ 33Table 4.3 Eastern end River Thames route drive options consideration of practical lengths ...... 34Table 4.4 Eastern end Rotherhithe route drive options .................................................................. 35Table 4.5 Eastern end Abbey Mills (via S8) drive options .............................................................. 36Table 4.6 Eastern end Abbey Mills route (via S7) drive options ..................................................... 36Table 4.7 Initial provisional main tunnel drive options matrix.......................................................... 39Table 4.8 Finalised main tunnel drive options matrix ...................................................................... 41Table 4.9 Thames Tunnel summary of drive options ...................................................................... 42Table 4.10 Programme assumptions for comparison of options .................................................... 43Table 4.11 Summary of construction duration differences for main tunnel drive options ............... 47Table 4.12 Summary of cost differences for main tunnel drive options .......................................... 48

LIST OF ABBREVIATIONS

AOD above Ordnance Datum

ATD above tunnel datum

CSO combined sewer overflow

Defra Department of Environment Food and Rural Affairs

EA Environment Agency

EU European Union

EPB earth pressure balance

GWT ground water table

LL1 Low Level Sewer No 1

m/s metres per second

m3/s cubic metres per second

NESR North East Storm Relief

OD Ordnance Datum (mean sea level at Newlyn in Cornwall)Ofwat Water Services Regulatory Authority

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PLA Port of London Authority

PS pumping station

SMP System Master Plan

SR storm relief

STW sewage treatment worksTBM tunnel boring machine

GLOSSARY

Term Description

Tunnel boring machine(TBM)

A machine used to excavate tunnels with a circular cross sectionthrough a variety of ground conditions.

Drive or Drive Option A possible tunnelling option for driving a tunnel from one location toanother with a TBM.

Slurry A mixture of bentonite and water to form a dense liquid capable ofsupporting open excavations such as bored piles and diaphragmwalls. Also used in TBMs to support the face and transport theexcavated material through a pumped system.

River Thames route One of three overall main tunnel routes considered. The RiverThames route terminates at Beckton STW and predominantlyfollows the River Thames, except for crossing the GreenwichPeninsula. This route is closest to the Option 1c tunnel routepresented in the December 2006 Tackling Londons Sewer

Overflows reports. This route has also previously been referred toas the baseline option and Option 1c-1. Drive option identifiersassociated with this route are generally prefixed with a B.

Rotherhithe route This main tunnel route is the same as the River Thames route,except that it cuts across the Rotherhithe Peninsula. This route hasalso previously been referred to as Alternative 1 and Option 1c-2.Drive option identifiers associated with this route are generallyprefixed with A1.

Abbey Mills route This main tunnel route terminates at Abbey Mills, using the LeeTunnel to convey flows to Beckton STW. This route has alsopreviously been referred to as Alternative 2 and Option 1d. Driveoption identifiers associated with this route are generally prefixed

with A2.

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1 Executive Summary

Page 1100-RG-ENG-00000-900006-Engineering-Options-Report.doc Printed 04/11/2010

1 EXECUTIVE SUMMARY

1.1.1 This report has been prepared for Thames Water as part of the process to support thecreation of the preferred list of shaft sites and preferred scheme. It is specific to theThames Tunnel Project, but takes cognisance of the Lee Tunnel Project. The need for thisreport and the process that it is part of is outlined in the Site Selection Methodology Paper,document reference 100-RG-PNC-00000-000025.

1.1.2 It is intended that this report is read as a technical document and, as such, the content hasbeen kept brief with the understanding that the reader has technical familiarity with thesubject matter.

1.1.3 The report begins by defining the overall engineering requirements that are to beconsidered as part of the development of engineering options. These are largelysummarised without providing any in-depth justification; the main aim of the report beingthe identification of main tunnel drive options.

1.1.4 Three main tunnel routes between west London and Beckton Sewage Treatment Works(STW) are identified as part of the design development and it is these that are takenforward separately for evaluation.

1.1.5 The second part of the report presents a methodology for determining possible options todeliver a scheme for the three main tunnel routes. This is based on engineeringrequirements and the list of shortlisted shaft sites provided by the site selection process,which identifies sites potentially suitable for use as either main tunnel drive orintermediate/reception shaft sites to facilitate the construction of the main tunnel and itssubsequent operation. Drive options for the connection tunnels in association with theshortlisted CSO sites are not considered in this report as they are dependent upon theselection of the main tunnel route and shaft sites.

1.1.6 To build the scheme, it is necessary to drive a tunnel or series of tunnels connecting anumber of shaft sites. Possible permutations of tunnel drive scenarios (drive options) forthe three tunnel routes and presented sites are established in a systematic manner topermit evaluation.

1.1.7 The relative desirability of the feasible drive options for the three routes are then examinedin terms of engineering factors, which are separated into engineering risk, programme andcost. These and the other discipline factors, such as planning, environment, communityand property, will ultimately be used in conjunction with the site suitability reports todetermine preferred sites and the preferred scheme, although this will be addressed insubsequent workshops and presented in the Preferred Scheme Report. It is also notedthat the relative merits in system performance of the three main tunnel routes are notdiscussed or considered within this report as these will be addressed separately by theproject team.

1.1.8 This report shows that appropriate engineering options are available to drive the maintunnel for each of the three main tunnel routes. These are presented as a schedule offeasible main tunnel drive options to be taken forward to the next stage of the siteselection methodology, and therefore the Preferred Scheme Report.

1.1.9 Finally, engineering factors that will be used to provide content for consultations and fordetermining the preferred sites and associated drive options for the three main tunnelroutes are also presented. These are the factors that will be used in the Preferred SchemeReport to examine the advantages and disadvantages, including engineering risk,programme and cost.

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2 Introduction


2 INTRODUCTION

2.1 Purpose of report

2.1.1 The Engineering Options Report has been prepared as part of the process for the creation

of the preferred list of shaft sites and preferred scheme as set out in the Thames TunnelProjects Site Selection Methodology Paper

1. The Site Selection Methodology Paper

states that the Engineering Options Report will consider:

how sites work in combination, and options for the main tunnel alignment andcombined sewer overflow (CSO) connections2

how options for tunnel alignment and CSO connection points will be refined, havingregard to the availability of and spacing of suitable shaft sites, as well as to thepotential for combined use of sites. Cost considerations associated with engineeringoptions, transport and energy will be reported, balanced and taken into account.3

2.1.2 This report identifies and refines possible main tunnel alignment options, givingconsideration to the overall location and grouping of the shaft sites that have been

shortlisted for site suitability assessment. Drive and alignment options for the CSOconnection tunnels are not included in this report as they depend on the selection of themain tunnel shaft sites, but they will be presented in the Preferred Scheme Report. Theestablishment of preferred sites, and hence preferred scheme, will follow on from thisreport. The findings of this Engineering Options Report will help inform the preferredscheme selection process.

2.1.3 The Engineering Options Report is divided into two parts:

Part 1: System design and engineering requirements

2.1.4 This part sets out at high level the system, geological, tunnelling and CSO engineeringrequirements to be considered as part of the development of engineering options, andsubsequent selection of both a preferred scheme and an associated preferred list of shaftsites. As such, this will largely state and summarise requirements without providing anin-depth justification for the system and engineering requirements.

Part 2: Engineering review and comparison of tunnel options

2.1.5 This part summarises the tunnel options considered and the analysis and refinement ofthese options. Included in the analysis is consideration of the relationship of the tunneloptions to the available groups of shortlisted shaft sites.

2.1.6 The report only considers the development of options from an engineering perspective.The considerations dealt with as part of the site suitability reports for each site have notbeen referred to in the preparation of this Engineering Options Report.

2.1.7 In considering main tunnel routes, drive options and shaft sites, this report does not identifypreferred tunnel routes, alignments, preferred shaft sites, connection tunnel routes or CSOsites. The selection of the preferred main tunnel route, alignments, connection tunnelalignments, preferred CSO sites and preferred shaft sites are to be assessed at laterstages in the process (selection of the preferred sites and preferred scheme). Thesestages will be carried out by a broader multidisciplinary team and reported in the PreferredScheme Report. The considerations in this Engineering Options Report, along with sitesuitability reports, will feed into and inform these stages.

1Site Selection Methodology Paper, document reference 100-RG-PNC-00000-000025 AA, Thames Tunnel,

(21 May 2009)2Site Selection Methodology Paper, Section 2.3.27, fourth bullet

3Site Selection Methodology Paper, Section 2.3.32

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2 Introduction


2.2 Background to project

2.2.1 The Thames Tunnel Project is required to intercept flows from CSOs along the RiverThames between west London and the Beckton STW in east London. It is needed forcompliance with Directive 91/271/EEC on Urban Waste Water Treatment and theavoidance of European Union (EU) fines. The project will benefit London as a whole, andthose living, working in and visiting London, by providing a cleaner River Thames. TheSite Selection Methodology Paperprovides further detail on the background to the project.

2.2.2 The Minister of State for Climate Change and the Environment issued a Ministerialstatement in March 2007 with reference to sewer overflows to the River Thames. This wasfollowed by a letter from the Minister, Ian Pearson MP, to Thames Water in April 2007,indicating that on the basis of the information supplied, it is the Ministers view that anOption 1 type approach is needed. Various options were presented in the December 2006reports, Tackling Londons Sewer Overflows, Thames Tideway Tunnel and Treatment Option Development, and were also discussed in Defras report, Regulatory ImpactAssessment sewage collection and treatment for London (March 2007).

2.2.3 The Option 1c solution, presented in the above referenced documents, consists of afull-length tunnel along the River Thames to intercept, store and convey to treatment thedischarges from 36 Category 1 and 2 CSOs. The Thames Tunnel Project controls flowsfrom 34 of the 36 CSOs, while the CSO (Abbey Mills) is controlled by the Lee TunnelProject, and the CSO (Wick Lane) by a standalone project.

2.2.4 It is noted that a further 21 Category 3 and 4 CSO are not to be controlled.

2.3 Engineering design development

2.3.1 Following the Ministers letter indicating the need for an Option 1 type approach, there hasbeen ongoing development of the main tunnel based on the Option 1c solution. The LeeTunnel has also been consented and the contract for its construction awarded.

2.3.2 The Thames Tunnel Projects site selection process4 recognises that the engineering

design will need to proceed in parallel with the site selection process, and that there is aniterative relationship between the two.

2.3.3 Design development activities have included:

engineering designs and studies of various components of the scheme, andidentification of possible high-level main tunnel routes

system master planning to define the sewage system operation changes andfacilities needed to control and limit overflows from the scheme

construction, transportation and river navigational logistics studies

field investigations, including ground investigations and surveys.

2.3.4 This Engineering Options Report draws on the relevant aspects of these studies and

investigations, as well as the results from the site selection shortlisting process.

4Site Selection Methodology Paper, Section 1.7.5

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3 System Design and Engineering Requirements


3 SYSTEM DESIGN AND ENGINEERING REQUIREMENTS

3.1 System design and engineering assumpt ions

3.1.1 The assumptions made for the preparation of this report are identified and listed in an

assumptions register in Appendix A (which can be found in the accompanying document,Engineering Options Report Appendices, reference 100-RG-ENG-00000-000009).These assumptions and further requirements are discussed in the following sections.

3.2 Health and safety cons iderations

3.2.1 Through risk assessment and management, the Thames Tunnel Project is working inaccordance with industry codes and project standards, with the aim to achieve world-classhealth and safety objectives. The project has a plan and policies in place to ensurecompliance with the Construction (Design & Management) Regulations 2007.

3.3 System requirements

Performance objective

3.3.1 The need for the project is described in the Site Selection, Background Technical Paper(Ref 100-RG-PNC-00000-000027).

Basis for the design and system development

General design requirements

3.3.2 The Site Selection, Background Technical Paperstates that the main features of theThames Tunnel Project were proposed to be:

the control of 34 combined sewer overflows within the tidal River Thames

the capacity to store the intercepted stormwater flows in a main tunnel

the ability to pump-out the tunnel to treatment.

3.3.3 The design development activities have progressed and, at the time of this report, theengineering requirements to be taken forward in assessing engineering tunnel route andalignment options are summarised and briefly discussed in the following sections. Thesedetails are the subject of ongoing work. However, for the basis of this report, it is notedthat the implications of any possible changes would need to be further assessed andreviewed.

3.3.4 To achieve the design performance and functionality requirements, the main tunnel isrequired to be a 7.2m internal diameter tunnel. This has been assessed to provide asystem with acceptable capacity to meet the requirements of the project.

3.3.5 This section of the report focuses on system requirements relevant to the selection of sitesand tunnel engineering alignments.

Developments in design requirements

3.3.6 Developments in the design have updated the scheme requirements such that 21 or 22CSOs are now required to be directly intercepted, depending on the main tunnel route,while the remaining CSOs are to be controlled by other measures. These measuresinclude three interceptions to the existing northern Low Level Sewer No 1 (LL1).

3.3.7 Table 3.1 lists the controls needed for all 34 CSOs, as well as indicating the 21 or 22 CSOs

requiring interception, and three additional interceptions to the existing LL1.

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Table 3.1 Details of combined sewer outfall

Combined sewer overflow Flow interception

CS01X Acton Storm Relief (SR) CSO flow is to be intercepted

CS02X Stamford Brook SR No modifications required

CS03X North West SR No modifications required

CS04X Hammersmith PS andCS04B LL1 Brook Green

CSO flow is to be intercepted

CS05X West Putney SR CSO flow is to be intercepted

CS06X Putney Bridge CSO flow is to be intercepted

CS07A Frogmore SR Bell Lane Creek andCS07B Frogmore SR Buckhold Rd


CS08A Jews Row Wandle Valley SR andCS08B Jews Row Falconbrook SR


CS09X Falconbrook PS CSO flow is to be intercepted

CS10X Lots Road PS CSO flow is to be intercepted

CS11X Church Street Indirect by action at Ranelagh/Western pumping station

CS12X Queen Street Indirect by action at Ranelagh/Western pumping station

CS13B Smith Street SR andCS13A Smith Street Main Line

Indirect by action at Ranelagh/Western pumping station

CS14X Ranelagh CSO flow and LL1 is to be intercepted

CS15X Western PS andCS15B Western PS upstream

Control modifications at Western pumping station

CS16X Heathwall PS CSO flow is to be intercepted

CS17X South West SR CSO flow is to be intercepted

CS18X Kings Scholars Pond SR Indirect by action at Ranelagh/Western pumping station

CS19X Clapham SR CSO flow is to be intercepted

CS20X Brixton SR CSO flow is to be intercepted

CS21X Grosvenor Ditch Indirect by action at Ranelagh/Western pumping station

CS22X Regent Street Indirect by action at Northumberland Street

CS23X Northumberland Street CSO flow and LL1 is to be intercepted

CS24X Savoy Street Indirect by action at Northumberland St/Fleet Main

CS25X Norfolk Street Indirect by action at Northumberland St/Fleet Main

CS26X Essex Street Indirect by action at Northumberland St/Fleet Main

CS27X Fleet Main CSO flow and LL1 is to be intercepted

CS28X Shad Thames PS CSO flow is to be intercepted

CS29X North East SR CSO flow is to be intercepted

CS30X Holloway SR CSO flow is to be intercepted

CS31X Earl PS CSO flow is to be intercepted

CS32X Deptford SR CSO flow is to be intercepted

CS33X Greenwich PS CSO flow is to be intercepted

CS34X Charlton SRCSO flow to be intercepted*/indirect by action at Greenwich pumping station**

* Applicable to the River Thames and Rotherhithe routes** Applicable to the Abbey Mills route

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3.3.8 Further elements that the scheme should provide as a minimum are listed below:

The westerly start point of the scheme should connect to the Acton Storm Relief(SR) CSO.

To meet hydraulic capacity and transient (temporary surge flow) requirements, themain tunnel (7.2m diameter) should extend to Hammersmith Pumping Station (PS)

in the west.

The easterly end point of the tunnel is to connect to the Lee Tunnel. This can beachieved at either Abbey Mills PSs or at Beckton STW.

The provision of three connections to the LL1 along the Chelsea and Victoriaembankments, where the high flows can be intercepted at new relief weirs. Theseflows will be diverted to the main tunnel and the operating philosophy of the WesternPS will be amended. These measures enable discharges at some other CSOs to becontrolled without the need for direct interception.

Relieving controlling flows at LL1, as well as the discharging sewers at the CSOsites required for Ranelagh, Regent Street and Fleet Main CSOs, gives sufficientcontrol to reduce local CSO spills so that direct interception is no longer required on

the Northumberland Street, Church Street, Smith Street, Kings Scholars Pond,Grosvenor Ditch, Savoy Street, Norfolk Street and Essex Street sewers. Thesebenefits rely upon the sites for the interception chambers being at locations thatallow the full design functionality to be achieved.

A system that ensures the health and safety of operatives, public and other thirdparties. This includes providing, during both the construction and operationalphases, a hydraulically safe and robust system without the risk of flooding oradverse transient conditions; secure and resilient facilities, appropriate levels ofventilation and air treatment, and safe methods and facilities for access and egressinto and from the main and connection tunnels.

3.3.9 At the time of writing, the system operational philosophy is under development. However,at a high level, the operational philosophy will be common to all options. Details of the

proposed operation will be developed separately and presented in separate systemengineering reports.

Main tunnel routes

3.3.10 Design development has identified three tunnel routes: The River Thames route,Rotherhithe route and Abbey Mills route.

3.3.11 The River Thames route largely follows the route of the Thames, while the two other routesprovide respectively an alignment that cuts across the Rotherhithe Peninsula and a routethat connects to the Lee Tunnel at Abbey Mills. The latter has become feasible due to anincrease in depth of the Lee Tunnel at the Abbey Mills PSs shaft end to avoid difficultgeological conditions. This enables a continuous gradient with the Thames Tunnel

Projects main tunnel, satisfying the design constraints for the overall vertical alignmentand system hydraulic requirements.

3.3.12 These three routes are displayed in Figure 3.1 and described as follows.

River Thames route (connection to Lee Tunnel at Beckton STW)

3.3.13 This route is closest to the route in Option 1c, shown in Defras report dated March 2007entitled Regulatory Impact Assessment sewage collection and treatment for London, buttakes account of over two years of additional development work, including the items statedin the General design requirements section above.

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Rotherhithe route 1 (across Rotherhithe Peninsula connection to Lee Tunnel atBeckton STW)

3.3.14 This is a variation to the River Thames route that cuts across the Rotherhithe Peninsula,reducing the River Thames route main tunnel length by 1.8km by not following a majorbend in the river. A longer connection tunnel conveys flow from the North East StormRelief (NESR) to the main tunnel, and a shorter connection tunnel is needed fromGreenwich PS. This route is otherwise the same as the River Thames route, byintercepting the Acton Storm Relief (SR) Sewer at its upstream end by connection tunnel tothe main tunnel, and connecting to the overflow shaft at Beckton STW at its downstreamend.

Abbey Mil ls route (connect ion to Lee Tunnel at Abbey Mil ls PSs)

3.3.15 This is different from the River Thames route because it connects the main tunnel to thehead of the Lee Tunnel at Abbey Mills. The main tunnel length would reduce byapproximately 9km. The upstream tunnel system would stay the same as the RiverThames route over the length from the interception of Acton SR to Rotherhithe, but theroute then veers northeast to Abbey Mills. A potential route/corridor for this length of

tunnel could follow the Limehouse Cut Canal. CSOs to be intercepted downstream ofRotherhithe would connect back to the main tunnel by connection tunnel, except CharltonSR, where alternative methods of control can be implemented.

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Figure 3.1 General layout of the three Thames Tunnel routes being considered

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Control and interception of CSO flows

3.3.16 The CSOs to be controlled and intercepted are outlined in the previous section and listed inthe assumption register provided in Appendix A. The register also indicates the minimumdiameter of the connection tunnels and drop shaft sizes for hydraulic purposes.

3.3.17 The interception of CSO flows and connection to the main tunnel typically comprises fourmajor elements: A CSO interception chamber, connection culvert, drop shaft andconnection tunnel, as shown in Figure 3.2 below. A description of the constructionelements is provided in the Site Selection, Background Technical Paperand these arediscussed further in CSO interception design and construction in Section 3.6.

Figure 3.2 Thames Tunnel CSO connection main system elements

Tunnel hydraulic requirements

3.3.18 The tunnel system is to store and convey flow, with the purpose of reducing CSOdischarge.

3.3.19 The internal tunnel diameter has been taken at 7.2m, which is compatible with the Lee

Tunnel.

3.3.20 The conveyance of flow is dependent upon the hydraulic grade line (rather than physicaltunnel gradient). To permit the hydraulic grade line (and therefore flow) to be containedwithin the system, the general top-of-structure level at the shafts could be as high as107.0mATD5. The interception chambers will not generally be subject to these higherlevels, due to the protection afforded by a range of flap valves (that prevent flow reversing).

3.3.21 The tunnel system has to be self-cleansing. This can be achieved by either the flowregime (physical gradient) or the provision of flushing water.

5This report reflects the information available at the time of writing, when it was anticipated that the elevation

of top structures at both CSO and shafts sites would be finished at 107mATD. Subsequent to the preparationof this report, this was changed to 104.5mATD, and this updated information has been used at later stages,such as the Preferred Scheme Report.

MAIN TUNNEL

Drive Shafts (not shown)provide principal

operational inspection

access

CONNECTIOTUNNEL

DROPSHAFTCONNECTION CULVERTOpen-cut or

Tunnelled/Jacked2 nr Flat gate chambers notshown and would naturally

form part of the Interceptionchamber and Drop Shaft

CSO INTERCEPTIONCHAMBER

Where CSO comprises

a PS the location of the

interception may be upor downstream of the

CSO PS

EXISTING OUTFALL

RIVER

Indicative of siteclearance and enabling

works

BECKTON STW

Inlet PSInlet works

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3.3.22 A gradient in excess of approximately one in 850 has been found to generate self-cleansing conditions with velocities exceeding 1m/s during event cycles. Based uponinternational experience, the self-cleansing velocity above this is sufficient to move detrituswithout further flushing requirements.

3.3.23 The gradient of the connection tunnels is generally in the range of one in 200 to one in 500in order to achieve flow capacities and maximum peak velocities. The minimum diameterfor these tunnels is to be 2m, to reflect the practicality of access for inspection byoperatives and to limit peak velocities.

3.3.24 Large tunnel systems are potentially prone to hydraulic pressure effects, due to thegeneration of transient (temporary surge flow) conditions. Control features therefore needto be incorporated into the tunnel design and mode of operation. These include:

the main tunnel diameter of 7.2m should extend to the Hammersmith PS to avoidover-pressurisation

provision of overflows6 to the river at main tunnel shafts

balancing the flows that are allowed to enter the tunnels with the volumetric capacityof the tunnels after allowing for rates of build up and evacuation of fluids and gases.

System functional and operational requirements

Operation and related safety requirements

3.3.25 In order to ensure safe operations, access, inspection and maintenance of the tunnel,design development has defined the following assumptions and features:

The main tunnel and connection tunnels are to be maintenance free, such thattunnel entry for inspection and maintenance is only planned to take placeapproximately every ten years.

The ten-year inspection will be a major undertaking in its own right, which will involve

elements of design and fabrication to permit entry. The system controlling tunnel filling is to be passive6 where possible to reduce the

need for maintenance/access and operational complexity.

Main tunnel drive shafts will be the designated access points to the tunnel system.The spacing of the main tunnel drive shafts is controlled by the requirements formaintenance access on the basis that the construction access demands are lessonerous, in view of what can be achieved with modern tunnelling techniques. Thespacing between permanent access points shall not exceed 9km, and shall bereduced to 5km or less where practicable. However, where main tunnelintermediate shaft access is available, this can be incorporated to improve theoverall access conditions and regime.

The main tunnel drive shafts shall be provided with large access openings to permitinspection plant to be lowered into the tunnel. CSO and shaft sites are to beselected to ensure space for two cranes to service the shafts.

The provision of permanent ventilation and monitoring of the exhaust air qualityalong with air treatment facilities (odour control).

The provision of control gates to isolate the tunnel system and prevent flow fromentering. These gates will be controlled from a central control room to permitoverview of the system from a single point.

6

This report reflects the information available at the time of writing, when it was anticipated that inflow wouldbe passively controlled and overflows to the river would be required at main tunnel shafts. Subsequent to thepreparation of this report, it was considered that overflows would not be required at all main tunnel shafts.

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Integrating the operating regime for the tunnel with the operating regimes atpumping stations, particularly Abbey Mills and Greenwich, along with Beckton STWand Crossness STW.

Due to the presence of pressure/pneumatic transients and the conveyance of foulwater, access ancillaries (eg, platforms, steps) shall not be provided as part of thepermanent works.

3.3.26 When considering the main tunnel shaft spacing for the completed system, and basedupon the experience from other major CSO systems, it is assumed maintenance andinspection teams will travel through the main tunnel by inspection vehicle. This reducesthe transit time and permits a wider range of equipment to be carried with relative ease.Vehicular access is practicable for this system, given the main tunnel diameter and that thesystem will be dry when inspection is undertaken.

3.3.27 Access to the connection tunnels will also be required during inspection. Connectiontunnel length is highly variable and site-dependent, ranging from 100m to 2,000m in length.Diameters are in the range of 2m to 5m. Provision for emergency egress will be made atthe drop shafts, by the provision of suitable access openings and space for cranes tooperate a man-rider.

3.4 Engineering geology

Route geology

3.4.1 The route geology has been established using the British Geological Survey (BGS)Lithoframe50 Model, from which geological long sections have been prepared. This isconsidered to be adequate for this report. Additionally, preliminary information fromongoing ground investigations has been taken into account for this report7.

3.4.2 Geological long sections, derived from the model, are provided for the three main tunnelroutes in Appendix D.

3.4.3 The basic geological horizons presented in the London Basin are given in Table 3.2.

7

This report reflects the information available at the time of writing. Subsequently, additional information andinterpretation of conditions have been available. This updated information has been used at later stages, suchas the Preferred Scheme Report.

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Table 3.2 Geology of London Basin

Era Group Formation Brief description of formationApproximate

range ofthickness (m)

Recent

Alluvium

Soft clays, silts, sands and gravels. May

contain peat. 0 - 5Floodplain Terrace

Kempton ParkTerrace

Medium to dense sand and flint and chert

gravel occasional cobbles and boulders.0 - 10

Tertiary Thames London Clay Very stiff, fissured silty clay. >100

Harwich

Swanscombe member:

Sandy clay to clayey sand (< 2m) withsome fine to medium black rounded

gravel.

Blackheath member:

Dense to very dense flint gravel (withoccasional cobbles) in silty or clayey,

glauconitic, fine to medium sand matrix.

Oldhaven member:

Very dense clayey sand with gravel andshells - often cemented as limestone.

0 - 10

LambethGroup

Woolwich

Reading

Highly variable material consisting ofgravel, sand, clay, silt, limestone, lignite

and calcrete.10 20

UpnorGravel, glauconitic and organic sand, silt

and clay. 5 7

Thanet Sands Formation (incl

Bullhead Bed at base 0.5m)

Very dense silty to very silty sand. The

lowest 0.5m consists of a conglomerate offlint pebbles. 10 15

Cretaceous Chalk Seaford*Homogeneous chalk with flint bands

(>100mm thick). circa 40

Lewes*Heterogeneous nodular chalk with flint

bands and marl seams. circa 50

Notes: * Limited to those formations of the White Chalk subgroup expected within the Thames TunnelProject. (Upper and Middle Chalk are now known collectively as White Chalk.)

3.4.4 The distribution of strata along the route is largely controlled by the London Basin Syncline,which plunges gently eastwards. Thus, beneath a cover of made ground and recentdeposits, the succession of tertiary deposits is gradually exposed west to east along theriver until the Chalk occurs at outcrop around Greenwich.

3.4.5 The anticipated geology at the proposed main tunnel invert is as follows:

London Clay Formation Hammersmith PS/Acton SR to just west of WandsworthBridge (Harwich at the base approximately between Wandsworth Bridge andVauxhall Bridge)

Lambeth Group just east of Wandsworth Bridge to Blackfriars Bridge

Thanet Sand Formation Blackfriars Bridge to just west of Tower Bridge

White Chalk subgroup all routes downstream from just east of Tower Bridge.

3.4.6 Faulting at London Bridge is expected to repeat the sequence, and mixed face conditionsin the Lambeth Group and Thanet Sand Formation are expected from Blackfriars Bridge

through to Tower Bridge, with only a short section wholly in Thanet Sand Formation, closeto Tower Bridge.

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3.4.7 Various structural geological models provide different interpretations of the structuralsetting across the London Basin, but they all generally indicate regular faulted blocktopography in the Chalk and NW by SE trending faults cutting the basic east-west mainsynclinal form.

3.4.8 The dominant structural geological features are:

the Greenwich Fault down throw 20m to 30m to the northwest in a series ofstepped faults. The fault runs generally parallel with the main syncline, SW to NEfrom Greenwich to Beckton, crossing the River Thames downstream of the ThamesBarrier.

the Greenwich Anticline sitting to the south of the Greenwich Fault and on a similartrend lifts Chalk to surface outcrop over the eastern section of the routes

the London Bridge Fault down throw 10m to the east.

3.4.9 Other structural features include the North Greenwich Syncline, Millwall Anticline andBeckton Anticline, all of which have a NE SW trend, contrary to main basin axis.

3.4.10 Scour hollows are located on previous drainage channels formed by the River Thames andare often found at the confluence with the existing tributaries, eg, at the Fleet, Lee and

Wandle. The features usually contain a variety of granular deposits and/or disturbednatural materials and are localised and steep-sided.

3.4.11 The scour hollow in the vicinity of the Blackwall Tunnel is the only scour hollow known topenetrate into the Chalk; elsewhere, the hollows only affect the tertiary deposits and, moreparticularly, the London Clay. Basal depths are normally 5m to 20m below ground level,exceptionally 33m at Battersea Power Station and 60m at Blackwall Tunnel.

3.4.12 Of the known scour hollows, only the hollow at Hungerford Bridge is close to the ThamesTunnel alignments. This feature attains a base level of 73mATD in London Clay near thesouth bank, equivalent to only 10m above the tunnel crown. Tunnel alignment shouldtherefore preferably follow a route close to the north bank. Such features may, however,have implications for the shallower connection tunnels in other locations.

3.4.13 Known scour hollow locations affect the following potential shaft and CSO sites:

S68WH (Battersea Power Station base 72mATD)

S87WH (Heathwall base 82mATD)

C23XA (Regents base 90mATD)

C27XA (Fleet base 90mATD).

3.4.14 The likely presence of flints within the Chalk may cause excessive wear to the tunnelboring machine (TBM), causing frequent interventions for inspection and maintenance, soan important part of the current ground investigations comprises the investigation of theChalk structure, Chalk permeability and characteristics of any flint band features.

3.4.15 A number of flint bands are present within the Chalk. However, within the Seaford Chalk,the two principal and well defined flint bands are the Bedwells Columnar and SevenSisters. The Bedwells typically comprise a discontinuous layer of very large irregular flintsup to approximately 500mm high by 300mm in diameter, and the Seven Sisters is acontinuous band, with flints between 100mm and 150mm thick. Both bands represent asignificant challenge to tunnelling that will need to be assessed when comparing route andalignment options.

Hydrogeology

3.4.16 The major aquifer of the London Basin lies in the Chalk, the aquifer being whollyunconfined to the east but confined to the west below the tertiary strata and the LondonClay Formation in particular. The Chalk aquifer is generally in hydraulic continuity with the

overlying Thanet Sand Formation and sometimes also the granular strata of the LambethGroup, particularly any local sand channels and the Upnor Formation. The EA refers tothis combined aquifer as the Chalk-Basal Sands aquifer.

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3.4.17 Local aquicludes can exist in the overlying Lambeth Group, leading to perched watertables. Historical records of engineering schemes have described these perched featuresto retain hydrostatic pressures of up to 40m, which may result in high inflows at tunnellevels and particularly in shafts during construction.

3.4.18 The Harwich Formation (Blackheath Member) is also known to contain high groundwaterlevels in places, which cause problems during tunnel construction.

3.4.19 A minor regional aquifer lies within the floodplain and river terrace deposits and because ofthe connection to the Thames, this aquifer is generally tidal, with an average level of100mATD (0mAOD) +/- 2.5m.

3.4.20 Regional monitoring of the Chalk aquifer is reported by the EA and specific monitoring datais available over the years 2000 to 2008. These indicate a depressed groundwater table incentral London at 60mATD, with water levels close to Blackfriars Bridge at 62mATD (referto the groundwater level contour plan of the London Basin in Appendix D). However, thelatest ground investigations are showing groundwater levels in the Chalk from Rotherhitheto Charlton 10m higher than the reported EA levels.

3.4.21 Groundwater pressure in the Chalk will have an important bearing on tunnelling. Table 3.3shows the 2008 levels in the Chalk aquifer eastwards from Tower Bridge, using the data

obtained from the EA.

Table 3.3 Chalk aquifer groundwater levels 2008 and imposed pressure at tunnel invert(east of Shad)

Tunnel sectionTowerBridge

NESR Greenwich Charlton Abbey Mills Beckton

Approx tunnelinvert mATD

50 45 46 40 40 32

Approx GWTlevel 2008mATD

72 78 91/100* 100 92m 100

Approx GWTpressure bar

2.5 3.5 4.5/5.5* 6.0 4.0 7.0

* Highest levels indicated in Lee Tunnel and Thames Tunnel Project monitoring holes

3.4.22 Short-term effects of pumping can still have a demonstrable impact on the regionalcontours. For example, levels decreased significantly due to abstractions in supply wells atBattersea/Brixton commencing in 2002, the water level being drawn down some 18m localto the wells, by 10m in central London near Fleet and by approximately 6m respectively inthe vicinity of Tower Bridge and the Battersea Power Station area.

3.4.23 The EA reports that the groundwater feeding the Chalk aquifer from the southeast interactswith the River Thames from Greenwich to Woolwich as it flows northwest to Stratford, then

west to central London. In the Greenwich to Woolwich area, there is potential for/evidenceof saline intrusion within the aquifer.

3.5 Tunnel engineering and construction requirements

Risk management considerations

3.5.1 The British Tunnelling Societys and the Association of British Insurers Joint Code ofPractice for Risk Management of Tunnel Works in the UK recommendations should beadopted for all significant tunnelling projects in the UK, including the Thames Tunnel. Theobjective of the code is to promote and secure best practice for the minimisation andmanagement of risks associated with tunnelling works and to set out best practices that

should be adopted. At the core of the code is an obligation that owners, designers andcontractors should have processes in place to identify and manage risks throughout the lifeof the project.

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3.5.2 The project has a risk management plan and procedures in place to manage and controlrisks and comply with the requirements of the Joint Code of Practice for Risk Managementof Tunnel Works in the UK. Refer also to Health and safety engineering risk considerationsinSection 4.

General tunnel considerations

Tunnel diameters

3.5.3 Tunnels should be sized to suit the hydraulic performance of the system and the storagecapacity requirement. This indicates that the main tunnel between its upper western endnear Hammersmith PS and Beckton STW needs to be a minimum 7.2m internal diameterthroughout its length.

3.5.4 Connection tunnels will connect CSOs to the main tunnel via drop shafts. These tunnelsshould be sized to carry the design flows from the CSOs at gradients to limit maximum flowvelocities to 3.5m/s, but not exceeding a maximum gradient of 1:200. The size of theconnection tunnels will vary, depending on the flow, from 2m to 5m internal diameter. Theminimum tunnel size for safe man access is assumed to be 2m internal diameter.

Vertical tunnel alignments

3.5.5 The vertical alignment of the main tunnel should follow an approximate gradient of aboutone in 850. The overriding criteria controlling the gradient that can be achieved are thehydraulic functional performance, the constraints imposed by existing and proposedthird-party infrastructure and the tunnel tie-in connection level at either Beckton STW orAbbey Mills PSs. The main third-party constraints are the Thames Water Lee Valley WaterTunnel near Hammersmith Bridge, and the proposed National Grid Wimbledon to KensalGreen tunnel.

3.5.6 The vertical distance separating the Lee Valley Water Tunnel and the main tunnel crossingabove would be about 5m. Other existing deep level service tunnels, including National

Grids Beverley Brook tunnel and a number of BT Openreach tunnels also presentconstraints on the alignment. In addition to these, the planned National Grid Wimbledon toKensal Green tunnel is also noted as requiring co-ordination to ensure that possibleinterference between these future projects is minimised. The distance between the tunneland other existing third-party underground tunnels is less critical to the vertical tunnelalignment.

3.5.7 The potential connection tunnel connecting Deptford SR and Greenwich PS CSOs to themain tunnel would be restricted vertically by the Jubilee underground line that crosses theRotherhithe Peninsula.

Horizontal tunnel alignments

3.5.8 There are three routes for the main tunnel between west London Hammersmith PS andBeckton STW or Abbey Mills PSs, described in Section 3.3 of this report.

3.5.9 These alignment options generally follow the line of the River Thames, particularly to thewest of Tower Bridge. There are numerous second order alignment options that areidentified and compared in Section 4 of this report. These must all satisfy the hydraulicflow regime requirements.

3.5.10 The minimum horizontal radius for the main tunnel is taken to be 600m for practicableconstruction purposes. Smaller diameter, segmental lined, connection tunnels are taken tobe typically of a minimum radius of 300m, although techniques can be employed toachieve lower radii.

3.5.11 In order to minimise the effect of tunnelling on third-party infrastructure, the tunnel should,so far as practicable:

pass under the centre of the mid-deck span of bridges

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avoid interfaces with sensitive existing structures, such as the original ThamesTunnel (Brunels Thames Tunnel, now carrying the East London underground line)and the Rotherhithe road tunnel

avoid passing beneath high-rise buildings on deep piles.

3.5.12 The alignment of CSO connection tunnels will generally be based upon the location of the

main tunnel and its shafts, along with hydraulic considerations.

Tunnel lining

3.5.13 The primary lining for the main tunnel is assumed to comprise a reinforced concrete,tapered, segmental lining ring, approximately 350mm thick and 7.8m internal diameter.This assumes a 300mm thick concrete secondary lining8 to provide the required finishedtunnel of 7.2m internal diameter. The connection tunnels are also assumed to have asecondary lining for the purposes of this report.

Shaft sizes

3.5.14 The main tunnel drive shafts are anticipated to be 25m internal diameter, with depths

ranging from 40m in west London to 65m or 75m in east London, depending on the maintunnel route. Shafts of 25m are considered to be the minimum size required to bothensure that a TBM can be launched and that all equipment required for safe construction ofthe tunnel can be accommodated.

3.5.15 The intermediate shafts and reception shafts for the main tunnel are assumed to have aninternal diameter of between 20m and 25m.

3.5.16 The internal diameter of CSO shafts range from 6m to 20m to suit the hydraulicrequirements, although at some locations, it may be advantageous to incorporate the CSOconnection culvert directly into a main tunnel shaft.

Location of main tunnel shafts

3.5.17 The preferred location of main tunnel shafts for construction from solely an engineeringviewpoint is influenced by the tunnel drive options and other considerations described inSection 4 of this report. In addition, consideration has been given to the followingfunctional requirements:

Every ten years, the tunnels will be inspected for operational and maintenancepurposes. Access to the main tunnel will be via main tunnel shafts. A safemethodology, including equipment, will be developed to reduce, where possible, theneed for additional intermediate shafts, simply to provide access between driveshafts. This is the basis of inspection and maintenance access for other large CSOschemes in the world.

The main tunnel shafts will incorporate weirs9 to allow spills into the River Thames

during full tunnel conditions. As a minimum, there would be an overflow weir atBeckton STW and two between Shad and the Charlton/Woolwich areas, and at leasttwo upstream of Wandsworth. This would need to be subject to further hydraulicmodelling.

8The decision about whether secondary lining is required has not be made at the time of writing this report,

but this report has been based on the assumption that it is required, as that represents the worst case forprogramme considerations.9

This report reflects the information available at the time of writing, when it was anticipated that overflows tothe river would be required at main tunnel shafts. Subsequent to the preparation of this report, it wasconsidered that overflows would not be required at all main tunnel shafts.

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Tunnelling and shaft construct ion methods

Tunnelling construction methods

3.5.18 The main tunnel has been assumed to have an external excavated diameter of 8.8m toprovide for a 7.2m internal diameter after allowing for the primary lining, secondary lining 10

and annulus grout thicknesses.3.5.19 In order to achieve a completion date in 2020, several TBMs will be required. In addition to

this, managing construction risk and the suitability of TBM types for the varying groundconditions along the route will also affect the determination of the number of TBMs to beused.

3.5.20 The geology and hydrogeology along each tunnel alignment will influence the selection ofthe TBM type. Full face TBMs will be required to support the ground during tunnelling toprevent excessive water inflows and excess excavation, and therefore minimise scope forground settlement.

3.5.21 The types of full face TBMs can be either earth pressure balance (EPB) or slurry/mixshield.However, convertible TBMs, which have been used in the past, can operate as either an

EPB or slurry machine but result in additional plant, equipment and impact to programme,to allow for changes to the operational method. For the purpose of this report, it has beenassumed that specific machines will be tailored to the ground conditions. These wouldtypically be EPB type TBMs for the main tunnel drives through the Lambeth Group west ofthe Shad PS area and also the London Clay, and slurry type TBMs for the eastern drivesthrough the Chalk.

Shafts construction methods

3.5.22 The geology, hydrogeology, depth and size of shaft will influence the method of shaftconstruction. Various methods of construction can be used, such as:

segmental lined caisson or underpinned construction

sprayed concrete lined

reinforced concrete sunk caisson

secant piled wall

diaphragm wall.

3.5.23 The construction of shafts in the London Clay is likely to be by conventional methods, withsegmental lining, sunk either as a caisson or underpinned. Sprayed concrete linings arealso possible.

3.5.24 Where the shafts are very deep, constructed through mixed ground conditions and underhigh groundwater pressures, diaphragm wall type construction is the most likely method ofconstruction. In general, the diaphragm wall type of construction requires a larger working

area than other methods of shaft construction. A diaphragm wall shaft is a reinforcedconcrete lined shaft, comprising individually installed, abutting vertical concrete wallpanels, constructed in the ground using specialist plant, prior to the excavation of theground within the centre of the shaft.

Ground treatment and control of groundwater

3.5.25 For all methods of shaft construction, the control of groundwater will be required to enableboth safe excavation and sinking of the shaft and base slab construction.

10

The decision about whether secondary lining is required has not been made at the time of writing this report,but this report has been based on the assumption that it is required, as that represents the worst case forprogramme considerations.

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3.5.26 In some locations, ground treatment may be required to improve the natural state of theground in advance of shaft construction or tunnelling. The term ground treatment coversa variety of techniques to strengthen or stabilise the ground:

Injection of chemical or cementitious grouts to form blocks that can be excavatedwithout collapse. The method used will be dependent on the ground encountered.

Ground freezing, where injection pipes circulate brine or liquid nitrogen to freeze thegroundwater and produce a stable block that can be excavated. Ground freezing iscostly and takes a long time to implement.

Compressed air, where a section of tunnel at the face has the air pressureincreased, using air locks and compressors. The air pressure is increased to resistthe inflow of groundwater. This technique has several health and safety implicationsand, with the 8.8m high face of the main tunnel, is unlikely to be completelysuccessful.

Dewatering to control the inflow of water into shafts and tunnel excavations, thusensuring excavation stability. This can take the form of either regional (widespread)or localised dewatering methods, depending on the purpose and the extent ofpressure reduction required. These methods will include deep borehole wells or

localised drains, well points and injector wells.

Main tunnel shaft site requirements

Main tunnel shaft sites

3.5.27 Three types of shaft site may be needed to construct the main tunnel: drive shafts,reception shafts and intermediate shafts.

3.5.28 The main tunnel will be driven from main drive shafts, which will be equipped to enable theefficient operation of the tunnelling excavation and construction.

3.5.29 Reception shafts will be used to remove the TBM from the tunnel at the end of a drive.

Given a sufficient size of site, a shaft could be used for both drive and reception purposes.

3.5.30 Intermediate shafts can be used to gain access to the main tunnel bore duringconstruction, either to inspect and/or maintain the TBM or to provide access for secondarylining construction (should a secondary lining be required).

Location of sites

3.5.31 The required number and distribution of sites for tunnel construction will be informed by thefollowing key considerations:

The Thames Tunnel Project is to be operational by 2020.

The TBM types must be appropriate to the geological conditions expected.

The risk of TBM breakdowns/servicing requirements, and their severity andfrequency, increases with the length of the drive.

The emergency egress of the construction workforce will become more difficult thelonger the length of the drive.

3.5.32 The final decision on the number of TBMs, and hence the number of associated drive shaftsites, will be based on a balance between the type of TBM appropriate to the ground, theavailable locations of main drive shafts, geology, programme, environment, amenity, healthand safety, risk and cost considerations.

3.5.33 Construction of CSO connection tunnels will, where possible, be constructed from mainshaft sites to reduce the space required for CSO sites. Where CSO connection tunnels aredriven from main tunnel shaft sites, the CSO drop shafts would comprise smaller reception

shaft sites. Excavated material from the CSO connection tunnel could also be handled atthe main tunnel shaft sites.

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Main tunnel drive shaft site requirements

3.5.34 The main tunnel drive shaft sites must provide for the following core and ancillaryconstruction activities for construction of the shaft and main tunnel:

Construction of 25m diameter shaft

Delivery of construction materials for shaft and tunnelling materials

Storage, treatment and removal of excavated material arising from the shaftexcavation and tunnel excavation

Material stockyard for tunnel segments and accessories, including loading/unloadingareas

Craneage and transfer of materials within the worksite and into and out of the tunnelshaft access

Grout batching plant

River access comprising jetty/wharf facilities for loading/unloading materials formarine transport

Workshops to maintain all the mechanical and electrical plant, and large stores forspare parts; stockyard for rails, pipes, grease, foam, cable drums, and temporaryworks items

Power supply installations with possible need for substation

Construction offices, welfare facilities and medical facilities

Parking for construction traffic

Incoming and outgoing goods and material marshalling area

Possible logistics hub area to service satellite sites.

3.5.35 In order to provide space for both core and ancillary activities, it is anticipated that main

tunnel drive shaft sites from which slurry TBMs will be driven will need to be approximately20,000m2, whereas sites hosting an EPB TBM will need approximately 18,000m2, in linewith the material handling requirements. The above areas do not allow for a logistics hub.

3.5.36 The construction activities that follow tunnel excavation are less onerous with respect tosite spatial requirements. These will include tunnel secondary lining (if required), shaftlining, buildings and surface works, and mechanical and electrical fit-out works.

Main tunnel reception shaft sites and intermediate shaft site requirements

3.5.37 Main tunnel reception shaft sites and intermediate shaft sites are not intended to be usedfor driving the main tunnel. Apart from providing access and egress points to the tunnel,the core activities to be undertaken from these shafts will be restricted to the constructionof the shaft itself, removal (at reception shaft sites) or access to (at intermediate shaftsites) the TBMs, secondary lining (if required) and mechanical and electrical fit-outactivities.

3.5.38 It is estimated that the areas required for both reception or intermediate shaft sites willrange from 5,000m

2for sites with shafts constructed into the London Clay to 7,500m

2, if

deep diaphragm walling is proposed for shaft construction into Chalk.

Construction logistics

3.5.39 For the purposes of this Engineering Options Report, the following logistical needs havebeen considered:

The ability to provide efficient site layouts

Logistics hubs

Critical services: Power and water

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Transport of materials and equipment

Main tunnel segment fabrication and supply.

Site layouts for logistics

3.5.40 The layouts of individual sites for the logistics purposes will depend upon the specific siteuse and local constraints. The Site Selection Background Technical Paperindicatestypical layouts for the different types of sites.

Logistics hubs

3.5.41 The supply and servicing of the smaller CSO sites could be carried out as satellites to themain tunnel drive shaft sites. These drive shaft sites may therefore require an allowancefor a logistics hub area for facilities to service the satellite sites.

Critical services: Power and water

3.5.42 The temporary power supply requirements for construction sites typically varies from

0.5MVA to 2MVA for the smaller CSO sites, and up to 11MVA to 14MVA for the large maindrive shaft sites serving a single TBM.

3.5.43 The number and potential spread of sites for main tunnel drives is such that for the majorityof areas, it is likely that insufficient capacity exists, or will be available from EDF Energy atthe time construction commences. Therefore, power supply improvement works would berequired.

3.5.44 Discussions with EDF Energy have established that it would be prudent to plan for theearly procurement of power supplies for the main drive sites. It is likely that power supplyimprovement works would be required because it is considered that there will beinsufficient capacity to accommodate this projects requirements. Drive shaft sites shouldtherefore be planned to accommodate new substation installations, for which an area of atleast 60m x 20m is required.

Transport of materials and equipment

3.5.45 Construction of the shafts and tunnel works would require a wide variety of materials andequipment to be transported to and from the working sites.

3.5.46 Excavated material will need to be taken away from the drive shaft sites and a wide varietyof materials would need to be delivered, particularly the concrete segments for the maintunnel lining. Other logistical activities will include workforce arrival/departure, equipmentdeliveries/return, consumables and, for the drive shaft sites, the delivery of the large TBMcomponents.

3.5.47 Due to the large volume of materials to be transported in and out of the main tunnel driveshaft sites, marine transport is the preferred option in order to minimise disruption to the

surrounding communities. However, barge operation will only be practical in the followingcircumstances:

Material can easily be conveyed between worksite and river

Barge facilities can be provided within the river (jetty/wharfage)

Barge movements can satisfy the logistics supply needs

Barge operations do not interfere with navigation or with other river users to anunacceptable degree.

3.5.48 The practicality of rail transportation will depend on both the proximity of the main sites tosuitable rail sidings and the local networks capacity for freight movements.

3.5.49 It is expected that some deliveries would be need to be transported by road, even if bargeand/or rail transport facilities were available. Any necessary highway routes will need to be

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identified as part of the project development. Major deliveries/removals will be subject tospecific movement restrictions and conditions imposed by police and traffic authorities.

3.5.50 For the majority of the CSO sites, it is envisaged that the primary mode of transport will beby road.

Main tunnel segment fabrication and supply3.5.51 The supply of tunnel lining segments to the individual drive shaft site locations will depend

upon their final location and the location of the potential fabrication facility or facilities.

3.5.52 It is considered that the supply of these could either be by road or river, while rivertransport would be preferred where practical and economic.

Excavated material handling and disposal

Material type and handling

3.5.53 The main excavated material types will be London Clay, Lambeth Group, Thanet Sands

Formation and Chalk. The overall route geology dictates where these are encountered.3.5.54 The type of material and TBM choice will dictate the material handling and treatment

requirements; the excavated material consistency will vary from relatively dry London Clayto Chalk slurry.

3.5.55 For the purposes of site planning, an allowance has been made for onsite storage ofexcavated material equating to five days production. This allows for issues relating tomaintenance, plant breakdown and risks to barge operations on the River Thames.

Quantities and programme requirements

3.5.56 The total quantity of excavated material for all tunnels and shafts is anticipated to be in theregion of 2.5 to 3 million m3 (in situ quantity). This will vary, depending on the tunnel

alignment and connections.3.5.57 The quantity of excavated material arising per drive at main tunnel drive shaft sites will be

approximately 300,000m3 to 500,000m3, assuming a tunnel length of between 5km to 8km.

3.5.58 Where two drives are carried out from the same site location, this will increase the capacityrequired if these are to be carried out simultaneously.

3.5.59 The tunnelling advance rates dictate the requirements for material removal. For thepurposes of preliminary planning, a rate of 2,000m3 to 4,000m3 per day from a site isassumed, depending on TBM type and ground conditions.

Marine transport

3.5.60 The feasibility and use of marine transport for the removal of excavated material frompotential main tunnel drive shaft sites along the river is dependent on location.

3.5.61 Operations in the upper reaches of the River Thames beyond Hammersmith Bridge areconsidered to be unworkable, due to the restrictions of bridge height, tidal range and widthof the navigable channel. These would impose constraints to barges that would reducesubstantially the quantity and rate of material that can be removed, making the viability ofsolely marine transport in these areas unacceptable.

3.5.62 The operations between Putney Bridge and Hammersmith Bridge are considered to bechallenging, especially when servicing the peak tunnelling rates. However, sites along thislength of the Thames could be accessed and serviced but would require careful planningto mitigate the problems associated with navigational constraints.

3.5.63 Downstream of Putney Bridge, there are fewer navigational constraints and, as such, it is

possible to use reduced numbers of larger size barges on the lower reaches of theThames to the east. Hence, only 350t barges can be used around Putney Bridge, 1,000t

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barges can be used in the vicinity of Battersea Power Station and 1,500t barges can beused from Greenwich to Beckton.

In-river facilities

3.5.64 Jetty/wharf structures and their location with respect to the navigational channel, together

with associated dredging of the river for access purposes, will be site specific. Each maintunnel drive shaft site not having substantial jetty or deep water wharf facilities is likely torequire a bespoke solution with specific consents from the Port of London Authority (PLA)and the EA.

3.5.65 The above issues, with respect to in-river facilities, are more onerous on the upper reachesof the river. Thus, beyond Hammersmith Bridge and to a lesser extent beyond PutneyBridge the scale of facilities for barges is likely to impinge greatly on the existing river andits users, leading to difficulties in obtaining the required consents.

3.5.66 Particular risks to in-river facilities and barge movements relate to other river users and theneed to obtain a marine risk assessment for operations. As such, it is noted that in theupper reaches of the river beyond Putney Bridge, the presence of recreational users, suchas rowers and small boats, presents a major hazard and risk to be considered when

evaluating sites.

Disposal of material

3.5.67 The total quantity of excavated material to be disposed of for the Thames Tunnel Project isin the region of 2.5 to 3 million m3 (in situ quantity). The methods of treatment, transportand disposal are dependent upon the nature and consistency of the excavated materialand requirements for final disposal.

3.5.68 The overall policy is to favour marine transport of excavated material along the RiverThames, where practicable.

3.5.69 The details of potential disposal sites are not discussed or considered in this report. Thesewill be covered by the project Waste Management Strategy, forming part of the future

Environmental Impact Assessment.

CSO connection to the main tunnel

3.5.70 Where the CSO connection tunnels are directly connected to the main tunnel, it has beenassumed that the internal diameter will be no greater than 3m and at an angle of about 70degrees to the main tunnel, unless there are overriding technical considerations, whichmean that this cannot be achieved. The limitation on diameter is due to constructionconstraints and the need to maintain structural stability of the main tunnel lining.

3.5.71 The CSO connections to the main tunnel are to be grouped into five generic options/types.These are outlined in greater detail in Section 4.

Connection with Beckton STW or Lee Tunnel

3.5.72 The main tunnel can either connect with the Lee Tunnel at Beckton STW or Abbey MillsPSs, depending on the main tunnel alignment. The details of these connections areoutlined below.

Beckton STW connection (for the River Thames and Rotherhithe routes)

3.5.73 For the River Thames and Rotherhithe routes, the main tunnel would connect to the LeeTunnel at the proposed overflow shaft at Beckton STW. The overflow shaft will becompleted as part of the Lee Tunnel prior to the Thames Tunnel Project. The connectionwill need to provide a smooth hydraulic path for flows in both directions, to allow bothtunnels to overflow to the River Thames when required, and for the construction of the

connection to minimise the effect on the Lee Tunnel operations.

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3.5.74 It is planned that the Lee Tunnel overflow shaft will make provision for the connection byincorporating a tunnel eye in the shaft wall. The Thames Tunnel Project will include a shaftapproximately 30m to one side of the Lee Tunnel overflow shaft, either to launch or receivethe main tunnel TBM. The two shafts will be connected by a short 7.2m internal diametertunnel.

Abbey Mills connection (for the Abbey Mills route)

3.5.75 For the Abbey Mills route, the main tunnel will connect to the Lee Tunnel at Abbey Mills.The proposed arrangement is for the main tunnel to connect at or close to the Lee TunnelShaft F (proposed Lee Tunnel shaft to be located at Abbey Mills PSs). The connectionwill need to provide a smooth hydraulic confluence to allow flows in both directions, and forthe construction of the connection to minimise the effect on the Lee Tunnel operations.

3.5.76 Two connection arrangements are considered feasible, although other arrangements maybe considered as the design develops:

The main tunnel connects directly into Shaft F. The Lee Tunnel Shaft F willincorporate a tunnel eye in the shaft wall for the connection.

A shaft approximately 50m to one side of the Lee Tunnel Shaft F will be constructed,either to launch or receive the main tunnel TBM. The Lee Tunnel will be enlargedover a short length to form a connection chamber and the Lee Tunnel and the maintunnel will be connected by a short tunnel.

Third-party infrastructure impact

3.5.77 The nature of operations involved in construction of the main tunnel and associated shaftshas the potential to cause ground movements that could affect existing third-partyinfrastructure and buildings. The horizontal and vertical alignment of the main tunnel shaftlocations and construction methodologies will be selected so that the impact on third-partyinfrastructure due to settlement will be avoided or minimised, as far as reasonablypracticable.

3.5.78 Searches of historical and other records have revealed wells located within the alignmentcorridor, some of which are operational abstraction wells. The tunnel alignment will,wherever possible, avoid any adverse affect on these wells.

3.5.79 Searches have revealed, in addition to road and underground rail transport tunnels, anumber of existing deep level service tunnels, including National Grids Beverley Brooktunnel and a number of BT Openreach tunnels. In addition to these, the planned NationalGrid Wimbledon to Kensal Green tunnel is also noted. The alignment of the main tunnelwill avoid these assets, with acceptable clearances.

3.6 CSO engineering and construction requirements

General considerations

3.6.1 The design requirements for CSOs are outlined in Developments in design requirements inSection 3.3 with a list of the controls required for all 34 CSOs, as well as indicating the 21or 22 CSOs requiring interception, depending on the route, and three interceptions to theexisting LL1.

3.6.2 The CSO interceptions identified comprise a combination of direct gravity overflows andpumping stations. In each case, the location of the CSO interception works will beconstrained by the layout of the existing sewer system.

3.6.3 In general, interception of gravity CSOs will be downstream of the last incoming connectioninto the overflow before the overflow sewer reaches the river, to ensure that the CSOinterception is not bypassed during a storm event.

3.6.4 For the interception of flows from pumping stations, there are advantages anddisadvantages associated with interception pre- and post-pumping. For example,

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intercepting the flows pre-pumping allows direct gravity interception without reliance on thepumps and therefore provides energy savings, whereas post-pumping interception allowsthe pumps to be used regularly and therefore provides maintenance benefits. In practice,the criterion governing whether pumping station flows are intercepted pre- or post-pumpingis likely to be the availability of suitable CSO sites.

CSO interception design and construction

3.6.5 The CSO interceptions typically consist of the following elements:

CSO interception chamber

CSO connection culvert

CSO drop shaft

CSO connection tunnel.

3.6.6 Details of each of these elements are outlined below.

CSO interception chambers

3.6.7 The CSO interception chamber will typically be a box-shaped structure and will bepositioned on the line of the existing sewer pipe. The purpose of this structure is tointercept the CSO flow and direct it into the connection culvert leading to the dropstructure.

3.6.8 The size of the interception chamber will be determined to suit the existing sewer and toaccommodate the maximum flow requirements for interception. This will be done followinga combination of theoretical and physical modelling.

3.6.9 The depth of the interception chamber will be determined by the depth of the existingsewer and, although relatively shallow, these can be up to approximately 22m deep,depending on the depth of the existing sewer at the location of interception.

3.6.10 It is envisaged that the interception chambers will be constructed as a reinforced concretestructure. However, the construction methodology for the chamber will be dependent onthe depth, ground conditions and other site specific criteria. Generally, sheet piling may beused to provide the excavation for the construction of the chamber. Where the depth of thechamber precludes the use of sheet piling, an alternative method, such as secant piling,may be required.

3.6.11 The existing line of the overflow is to be retained for use as an overflow for the system inthe permanent case. An overflow is also to be maintained during the construction of theinterception works to enable the function of the existing system to be maintained in a stormevent within this period.

3.6.12 For foreshore interception options, it is envisaged that the interception chamber may beincorporated within the top of the drop shaft.

3.6.13 The overflow to the river will be protected by double isolation in the form of two lines of flapgates. These flap gates will either utilise the existing flap gate arrangement (whereacceptable) or, in some cases, a new structure and flap gate arrangement.

3.6.14 The interception chamber will also be protected against reverse surcharge flows from thedrop shaft by means of two lines of flap gates located on the line of the proposedconnection culvert. An actuated, motorised penstock will also be positioned within theinterception chamber at the junction of the connection culvert. This penstock will remainopen during normal operative procedures, but will be closed to prevent flows being divertedthrough the connection culvert during maintenance activities.

3.6.15 It is envisaged that a control kiosk will be required at each CSO interception site to operatethe motorised penstock. This kiosk may also be used to accommodate other control andmonitoring equipment and will be sized accordingly.

3.6.16 An opening will be required in the roof of the interception chamber to facilitate maintenanceaccess and to allow for repair or replacement of the flap gates and penstock in the future.

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These openings will be fitted with suitable lockable covers. It is envisaged that the roof ofthe chamber will be at or below ground level, with the covers to the openings positioned atground level.

CSO connection culverts

3.6.17 The CSO connection culvert will join the interception chamber to the drop shaft. It is theintention to minimise the length of the CSO connection culvert by positioning the chamberand shaft as close together as possible, although this is dependent on the individualconstraints at each site.

3.6.18 The depth of the connection culvert will typically be determined by the depth of the existingsewer, which in turn sets the depth of the interception chamber. In some cases, it may berequired to increase the depth of the connection culvert to minimise impact on third-partyassets, particularly if the culvert has to pass under existing structures or utilities.

3.6.19 The connection culvert will be sized to accommodate the required controlled or maximumdesign flow rate.

3.6.20 The form of construction of each CSO connection culvert will be controlled by the

constraints at each site. Typical forms of construction could include open cut supported bysheet piling, microtunnelling/pipejacking (utilising precast concrete pipe units) andheadings. Therefore, the connection culvert may be either circular or box-shaped in crosssection and could comprise precast concrete pipes, precast concrete culvert units or in situconcrete.

3.6.21 There may also be a series of access manholes along the length of the culvert toaccommodate the required flap gates and to provide maintenance and inspection access.

3.6.22 For foreshore interception of CSOs, the interception chamber may be accommodatedwithin the top of the drop shaft and no connection culvert would be required.

CSO drop shafts

3.6.23 The purpose of the drop shaft is to allow the intercepted flows from the CSO to be droppedto the level of the main tunnel or, in some cases, to the level of the connection tunnel.Three forms of mechanism have been considered to drop the flows within the drop shaft.These are summarised as follows:

3.6.24 Straight drop: The use of a straight drop is only considered appropriate where the drop inheight is less than 10m due to energy dissipation. The direct drop approach will maintainthe flow within a pipe rather than being a waterfall. For the majority of CSOs, the drop inheight is greater than 10m and therefore a straight drop will not be used.

3.6.25 Cascade drop: Cascade platforms within shafts are used to dissipate energy for dropsgreater than 10m. The cascade typically includes alternating platforms at approximately3-6m intervals over the full depth of the shaft, causing the energy to be dissipated in stagesas the flows drop to the required level. Due to the regular inspection and maintenance

regime required for cascade type drops, and the associated health and safety issues,cascade type drop shafts are not preferred.

3.6.26 Vortex drop: Vortex drop tubes can be used for drops greater than 10m. In order togenerate the vortex at the top of the drop tube, vortex tubes are envisaged to be in therange of 0.9m to 3m diameter.

3.6.27 Drop shafts will be sized to accommodate maximum flows, having regard to themechanism used to drop the flow to tunnel level. The assumptions register in Appendix Aprovides the assumed minimum sizes.

CSO interceptions and connection to main tunnel

3.6.28 For the River Thames and Rotherhithe routes, 22 CSOs will be intercepted and connected

to the main tunnel, along with three low level sewer connections as detailed in

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Developments in design require

Documents

100-RG-ENG-00000-900006-EOR_Spring 2010