guidance notes for developments or engineering works in the

GUIDANCE NOTES FOR DEVELOPMENTS OR ENGINEERING WORKS IN THE VICINITY OF SPT SUBWAY INFRASTRUCTURE

JULY 2005

Glasgow Subway Guidance Notes for Developments

CONTENTS

1.0 INTRODUCTION

2.0 OVERVIEW OF SPT APPROACH TO DEVEOPMENTS/WORKS IN THE VICINITY OF ITS SUBWAY INFRASTRUCTURE

3.0 SPT APPROACH TO DEALING WITH APPLICATIONS FOR DEVELOPMENTS/ WORKS IN THE VINCINITY OF ITS SUBWAY INFRASTRUCTURE

4.0 EXISTING SUBWAY INFRASTRUCTURE

5.0 INFORMATION SBMISSION TO SPT

6.0 CRITERIA USED TO ASSESS DEVELOPMENT PROPOSALS

7.0 MITIGATION MEASURES

8.0 POSSIBLE CONSTRAINTS/RESTRICTIONS ON DEVELOPMENTS

9.0 SPT CONTACT INFORMATION

10.0 REFERENCES

11.0 APPENDICES

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1.0 INTRODUCTION

1.1 The purpose of this document is to provide information and initial guidance for those

involved with proposed new building developments, demolition works, or other engineering

works in the vicinity of Strathclyde Passenger Transport (SPT) Subway Infrastructure.

1.2 This document is intended to give initial guidance on the SPT’s requirements, with regard

to safeguarding Public Safety and its Subway Infrastructure, prior to detailed consultation

with SPT regarding any specific proposed development in the vicinity of the Subway

Infrastructure. For the purposes of this document, SPT’s Subway Infrastructure is defined

as all subway tunnels, station buildings, station chambers and Broomloan Yard and Depot.

1.3 This document presents a framework for the presentation of data required by SPT, such

that the risk to public safety and Subway Infrastructure can be assessed. It also presents

the criteria by which SPT will assess the presented data.

1.4 The information contained in this document is necessarily general in nature and does not

provide site specific information or guidance. Where new building developments or other

engineering works are planned, in the vicinity of SPT’s Subway Infrastructure, contact

should be made with the SPT to discuss the proposal and establish SPT’s site specific

requirements. Contact details are given in Section 9 of this document.



2.0 0VERVIEW OF SPT APPROACH TO DEVELOPMENTS / WORKS IN THE VICINITY OF ITS SUBWAY INFRASTRUCTURE

2.1 SPT has statutory obligations to ensure that its facilities are safe for the Public to use. It

also has commercial obligations to maintain and protect its infrastructure. These

obligations must be balanced against the commercial and social needs of the city to

regenerate and prosper.

2.2 SPT’s approach is therefore to work together with those seeking to develop / re-develop in

the vicinity of its Subway Infrastructure, to ensure that both Public Safety and the Subway

Infrastructure is protected, whilst allowing development / re-development to be carried out.



3.0 SPT APPROACH TO DEALING WITH APPLICATIONS FOR DEVELOPMENTS / WORKS IN THE VICINITY OF ITS SUBWAY INFRASTRUCTURE

3.1 General

3.1.1 The onus is on the developer to demonstrate that the proposed demolition / development /

works will not have an adverse effect on SPT’s Subway Infrastructure. The level of detail

required to do this, is dependent on a number of factors, principally :

• The location of the proposed development / works, in relation to the Subway

Infrastructure.

• The type of foundation and the foundation level, for the proposed development / works,

in relation to the Subway Infrastructure.

• The magnitude of the foundation loads of the proposed development / works.

• The proposed demolition / construction methods, for the proposed development /

works.

3.1.2 In general, the closer the proposed demolition / development is to the Subway

Infrastructure, and the higher the demolition / foundation loadings, then the more detailed

the information and study that will be required, in order to demonstrate that the Subway

Infrastructure is not adversely affected.

3.1.3 Initial guidance is given in Appendix 5 of this document, with regard to the likely level of

detail that will be required by the SPT. However, as noted above, site specific proposals

should be discussed in detail with the SPT, once the scope of the development is known.

3.1.4 It should be noted that due to the different ground conditions through which the tunnels are

constructed and the different types of construction adopted in the original tunnel

construction, over the length of the Subway, SPT requirements may differ for similar

development proposals constructed on different sites.



3.2 Costs

3.2.1 All cost associated with satisfying SPT requirements will be borne by the developer.

3.2.2 For large demolitions / developments, close to or over the Subway Infrastructure, this may

include :

• Costs of employing an independent engineer, on behalf of, and to be selected by SPT,

to review the proposals.

• Costs of strengthening works to the tunnels.

• Costs of insurance protecting the SPT against loss of earnings and any required

remedial works, should there have to be an unplanned temporary closure of the

Subway, during adjacent construction works.

• Costs of entering into a legal agreement with SPT prior to commencement of

construction works.

• Costs of any intrusive investigations.

• Costs of before and after dilapidations surveys.

• Costs of monitoring the tunnels during construction..

3.3 Timescales

3.3.1 Timescales, from initial discussions with SPT, to commencement of construction works will

vary dependant on the nature of the proposed development and the quality of information

submitted for review. It is recommended that proposals are discussed with SPT as soon

as the scope of the development is known.

3.3.2 Indicative timescales, can vary from a few weeks for a small development with little

influence on the Subway Infrastructure, to 12 months for a large development, at shallow

depth, directly over the tunnels. Every effort should be made to make contact with SPT, for

initial discussions, six months before the proposed construction works.



4.0 EXISTING SUBWAY INFRASTRUCTURE 4.1 General

4.1.1 SPT Subway Infrastructure comprises a circular layout of twin tunnels, 10.54 km in length,

serving 15 stations around Glasgow city centre. The system was opened in 1896 and with

the exception of modernisation works carried out to the stations in the late 1970’s and

regular maintenance works, the tunnel infrastructure remains as originally constructed.

The tunnels are 3.35m (11ft) in diameter, with different construction materials used to

accommodate the varying ground conditions encountered along the tunnel route, and

different forms of construction adopted by the different contractors, employed on the

various sections of the system.

4.2 Tunnel Location 4.2.1 A map indicating the approximate location of the Subway tunnels is included in Appendix 1

of this document. Reference should be made to current large scale Ordnance Survey

maps for more accurate information; however it should be noted that the information

indicated on these maps is not precise and where developments are proposed close to the

Subway Infrastructure, topographical surveys will be required to accurately confirm the

relative positions of the tunnels to the proposed development / works. SPT can provide

detailed Ordnance Survey maps indicating the line and level of the Subway tunnels on

request.

4.3 Tunnel Depth

4.3.1 The depth to crown of the tunnels varies from 1m to 35m below ground level. Indicative

depths to the tunnel crown, below existing ground levels, are indicated on the plan included

in Appendix 2.

4.3.2 Approximate tunnel levels can be obtained for site specific proposals from SPT.



4.4 Tunnel Construction

4.4.1 Cast iron segments have been used, principally beneath and adjacent to the river

crossings and in areas of poor ground, elsewhere there are sections of circular brick or

mass concrete horseshoe shaped lining. Where sections of the tunnel have been

constructed by cut and cover methods, the construction is a combination of mass concrete

and brickwork. A plan and sections, indicating the type of construction of the various

sections of the Subway Infrastructure are indicated in Appendices 3 and 4.



5.0 INFORMATION SUBMISSION TO SPT 5.1 General

5.1.1 The purpose of the information submission to SPT is to provide an objective engineering

assessment of the effects of the proposed development on SPT’s Subway Infrastructure. It

is anticipated that the services of a suitably experienced and qualified geotechnical / tunnel

engineer, with proven competency to carry out this work, will be employed by the

developer.

5.1.2 In order to minimise the time taken by the SPT to review the proposals, the information

should be submitted as a comprehensive package, the requirements for which, having

been discussed and agreed with SPT, prior to submission.

5.1.3 The package submitted to SPT shall be in report form, with appendices giving supporting

documentation. As a minimum, the package shall incorporate the following :-

1. Introduction to the proposed development, giving an overview of the proposals and

contact details for the developer, engineer and architect.

2. CV of developer’s geotechnical / tunnel engineer.

3. Details of the site ground conditions, in the form of an interpretative report.

4. Detailed information on the development proposals.

5. An assessment of likely impact that the development shall have on SPT infrastructure.

6. Actions to mitigate the impact of the development.

7. Monitoring proposals.

5.1.4 An initial guide to additional SPT information requirements, with respect to foundation

proximity and foundation type / loading are given in Appendix 5.



5.2 Further details in relation to points 3-7 above are given below:

5.2.1 Detailed Site Ground Conditions

5.2.1.1 A desk study should be carried out reporting the recorded geology of the area, previous

mineral / mining activities and investigation, the historical uses of the proposed

development site, land ownership details and the locations of services.

5.2.1.2 In general, in order to predict the effects of a development in the vicinity of SPT’s Subway

Infrastructure, a comprehensive ground investigation will be required, to establish the

ground characteristics. The information from the ground investigation should be presented

in the form of an interpretative report, giving due consideration to the proposed

development and the Subway Infrastructure.

5.2.1.3 In addition, a mineral/mining desk study and if necessary intrusive investigation will be

required, to determine if old mine workings exist in the area of the proposed development.

Where they exist, an assessment of risk posed by the presence of mine workings on the

development and subway infrastructure, will be required.

5.2.1.4 Ground investigation boreholes shall not be installed any closer than 9m to the tunnel lining

as indicated on current 1/1250 Ordnance Survey maps. SPT should be contacted, where

site investigations closer to the tunnels are required.

5.2.2 Detailed Information on Development Proposals

5.2.2.1 Detailed information defining the proposed development will require to be submitted, as a

minimum this will include :

• The location of the proposed development relative to the SPT’s Subway Infrastructure.

As a minimum, the site limits of development shall be shown clearly on a 1:10,000

Ordnance Survey plan. The closer the development is to the tunnels, the more

accurate the survey and setting out that will be required.

• The type and size of foundations proposed, together with their associated loads.

• The foundation geometry.



Where developments fall into category B and C of Appendix 5 more detailed submissions

will be required, in increasing content, depending upon the complexity of the development

and interaction with the subway infrastructure.

Typically this will include:

• Ground investigation establishing ground stratification and soil / rock characteristics.

• Calculation of the stress increase in the ground surrounding the tunnels.

• Predicted ground movement.

• Change in stress of the tunnel lining.

• Tunnel deformation estimates.

5.2.2.2 Where demolition works are to be carried out within 35m of the Subway Infrastructure, then

the specific proposals should be discussed with SPT. Information requirements will

depend on the scale and proximity of the demolition works together with the proposed

method of demolition. As a minimum, demolition method statements will be required.

Where the demolition methods proposed are likely to lead to significant changes in loading

or cause vibration in the Subway Infrastructure, then additional information will be required,

which will allow the effects of the proposals to be assessed against the criteria listed in

Section 6 below.

5.3 Assessment of Development Proposals on the Subway Infrastructure

5.3.1 A study demonstrating the predicted impact of the development proposals on the Subway

Infrastructure shall be undertaken appropriate to the scale of the development proposed.

5.3.2 For lightly loaded foundations, remote from the Subway Infrastructure, simple analytical

methods may be used.

5.3.3 For heavily loaded and complex foundation arrangements more detailed geotechnical and

structural calculations will be required, to ascertain the change in condition of the tunnels

and their environs, and the potential effect on the structural integrity of the tunnel. This

may require the use of Finite Element Analysis, or similar, to assess fully possible changes

in conditions.



5.3.4 In addition to determining potential changes in stress within the tunnel lining and

deformation of the lining and surrounding ground, depending upon the extent of estimated

deformation, an assessment may be required to ascertain any change to the kinematic

envelope and/or gauging of the running track within the subway.

5.3.5 Where the effects of the development are excessive, or deemed unacceptable by SPT, the

developer will require to design and incorporate appropriate mitigation measures to provide

a safe and suitable operational infrastructure.

5.4 Measures to mitigate vibrations and noise from the Subway Infrastructure on the proposed development

5.4.1 Depending on the nature of the development and its proximity to SPT’s Subway

Infrastructure, there may be a requirement to incorporate sound or vibration absorption

measures into the development proposals. SPT make no warranty to limit noise and

vibration emanating from the Subway infrastructure.

5.4.2 It should be noted that SPT is not liable for any costs associated with the assessment or

provision of such measures.



6.0 CRITERIA USED TO ASSESS DEVELOPMENT PROPOSALS 6.1 General 6.1.1 Once SPT receives the above data package, it will then be in a position to assess the likely

impact of the development, on the infrastructure. Submitting data in a manner that departs

from the above, or is incomplete or ambiguous may lead to delays in assessing proposals.

6.1.2 As guidance, adverse effects on the Subway Infrastructure can result from :

• Ground deformations and tunnel lining stress change due to loading or unloading of the

ground surrounding the tunnel.

• Changes in the ground water table levels around the tunnel.

• Ground vibrations due to piling or other construction work.

6.1.3 As a guide, where the following limits are not exceeded, the development proposals would

generally be deemed to be acceptable to SPT :

• predicted movements of the tunnels of less than 1 mm;

• predicted stress change in the tunnel lining of + or – 5%;

• predicted vibration at the tunnel lining of a peak particle velocity of less than 2.7mm/s

6.1.4 However as noted above, each development is considered by SPT on a case by case

basis and exceptions to the above will occur.



7.0 MITIGATING MEASURES 7.1 General

7.1.1 SPT will review the foundation proportions, the technical assessment of likely impact of the

development on the infrastructure and any mitigative measures proposed. There should

be a demonstrable philosophy linking the mitigative measures with reducing risk to the

tunnels.

7.1.2 In general terms, SPT regard foundation design and construction specification as the

primary mitigative action. The most obvious measure is to spatially arrange the proposed

development so that the most heavily loaded foundations are furthest from the Subway

Infrastructure. Alternatively, the structural arrangement of the proposed development can

ensure that the load paths take the structure loads to foundations located remotely from the

Subway Infrastructure.

7.1.3 Where heavy foundation loads in the vicinity of the Subway Infrastructure cannot be

avoided, then non-displacement piles, founded below the tunnel formation level will

generally be required. Additional pile slip linings/coatings and limits on construction

methods may also be required, depending on the ground conditions / pile proximity to

tunnels.

7.1.4 For developments proposed in close proximity to the Subway Infrastructure, tunnel lining

strengthening works may also be required. This may take the form of grouting, bolting

and/or reinforcement of the lining or similar intrusive works within or outside of the tunnels.



8.0 POSSIBLE CONSTRAINTS/RESTRICTIONS ON DEVELOPMENTS 8.1 Prior to Construction

8.1.1 To minimise disruption, the time required for the activities associated with interfacing with

the SPT, should be included in the development programme.

8.1.2 Dependant on the nature of the development, SPT may require that detailed construction

method statements are submitted, for agreement, prior to any construction work

commencing. Contractual arrangements for the works should therefore take cognisance of

this requirement.

8.1.3 For development proposals which require a close control on construction works, SPT may

require that the developer enters into a legal agreement in order to ensure that SPT

interests are protected.

8.1.4 Contractual arrangements for the development should ensure that one organisation / agent

is responsible for ensuring compliance with SPT’s requirements throughout all stages of

design and construction of the development.

8.2 During Construction

8.2.1 Where tunnel strengthening or monitoring works are required, then they will require to be

carried out during night-time track possessions, under the access control of a SPT

Flagman.

8.2.2 Depending upon the extent of the scheme a detailed pre-works condition survey will be

undertaken of the tunnels and their environs; followed by periodic inspections and reports

during the period of construction.

8.2.3 Depending on output of the detailed studies carried out to predict the impact of the

development on the Subway Infrastructure, instrumentation and monitoring of the tunnels



may be required in order to validate the predictions made. This may range from simple

vibration monitoring to sophisticated electrolevel and tunnel lining stress monitoring.

8.3 Post Construction

8.3.1 “As built” record drawings of the works in the vicinity of the Subway Infrastructure may be

required to be submitted to SPT on completion of the development.

8.3.2 A condition survey of the tunnel will be carried out immediately after construction and depending upon the extent of the works at quarterly intervals thereafter for a period of one year. Should any defects be identified then these shall be corrected immediately by the developer, in agreement with SPT.


9.0 SPT CONTACT INFORMATION


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9.1 For further information, please contact :-

Engineering

SPT Glasgow Subway

Broomloan Depot

Robert Street

GLASGOW

G51 3HB

Telephone No :- 0141 333 3159 Email :- [email protected]

mailto:[email protected]


10.0 REFERENCES

10.1 Paper titled “Centenary of the Glasgow Subway 1896 – 1996” by JS Shipway

`Proceedings of the Institution of Civil Engineers; Civil Engineering, 1996, 114, Aug 130-

139

10.2 Special Requirements and Specifications for Working in Tunnels

Available from SPT on request.



11.0 APPENDICES

11.1 Appendix 1 – Plan of Subway indicating approximate location.

11.2 Appendix 2 – Table indicating approximate minimum and maximum depths to crown of

tunnels.

11.3 Appendix 3 – Plan of Subway indicating approximate extent of construction types

11.4 Appendix 4 – Typical sections through the various construction types

11.5 Appendix 5 - Simplified zoning diagram indicating likely SPT information requirements


APPENDIX 1

PLAN OF SUBWAY INDICATING APPROXIMATE LOCATION.

Scale 1:10,000 @ A2

Crown copyright and database rights 2014 Ordnance Survey 100023445 ©

Contact SPT if you are thinking about carrying out anydemolition, development, site investigation or utilityworks within the yellow shaded area marked.

Subway Consultation Zone

Extent ofBuffer Area

Partick

Kelvinhall

Hillhead

Kelvinbridge

St. George’s Cross

Cowcaddens

Buchanan St

St. Enoch

Bridge St

West StShields Rd

Kinning Park

Cessnock

Ibrox

Govan

NAPPENDIX 1

APPENDIX 2

TABLE INDICATING APPROXIMATE MINIMUM AND MAXIMUM DEPTH TO CROWN OF

TUNNELS

DEPTH OF COVER TO SUBWAY

TUNNELS

Stations Minimum (m) Maximum (m)

Kelvinbridge to St Georges Cross 5 13.3

St Georges Cross to Cowcaddens 6.4 8.4

Cowcaddens to Buchanan St 7.9 22.4

Buchanan St to St Enoch 6.3 8.5

St Enoch to Bridge St 3.6 15.2

Bridge St to West St 1.5 9

West St to Shields Rd 3.8 4.8

Shields Rd to Kinning Park 2.3 7.7

Kinning Park to Cessnock 2.4 3.5

Cessnock to Ibrox 1 6.4

Ibrox to Govan 2.2 4

Govan to Partick 3.2 18.8

Partick to Kelvinhall 3.7 6.3

Kelvinhall to Hillhead 2.8 11.8

Hillhead to Kelvinbridge 5 35.6 (Mid Point)

APPENDIX 3

PLAN OF SUBWAY INDICATING APPROXIMATE EXTENT OF CONSTRUCTION TYPES

APPENDIX 4

TYPICAL SECTIONS THROUGH THE VARIOUS TUNNEL CONSTRUCTION TYPES

APPENDIX 5

SIMPLIFIED ZONING DIAGRAM INDICATING LIKELY SPT INFORMATION REQUIREMENTS

Examples Example 1 – Proposed construction of a two storey building with foundations 12m above and 25m minimum horizontal distance from the Subway Infrastructure to the proposed development. The foundations comprise generally of 900mm wide reinforced concrete strip footings, with a maximum un-factored bearing pressure of 220kN/m2. This proposal falls into foundation zone 4.1, and foundation type M (refer Fig A5.1), therefore it is sufficient to advise SPT of the proposed development and that, due to the location and type of the proposal, that no additional information is required, other than if demolition is involved. Example 2 - Proposed construction of a five storey building with foundations 2m above and 7m minimum horizontal distance from the Subway Infrastructure to the proposed development. The foundations comprise generally reinforced concrete pad footings of various sizes up to 3m square, with a maximum un-factored bearing pressure of 240 kN/m2. This proposal falls into foundation zone 2.2, and foundation type M (refer Fig A5.1), therefore the following information is likely to be required as a minimum (see cat B – fig. A5.1) :

• Scale plan and section of proposed development relative to the subway infrastructure • Structure type • Foundation type, level and loading • Construction methods proposed • Ground investigation establishing stratification of site and soil / rock classification and characteristics • Calculation of stress increase in the ground surrounding tunnels

Example 3 - Proposed construction of a six to seven storey building with ground level 12m above the Subway Infrastructure and piled foundations 6m horizontal distance from the extrados of the Subway tunnel to the proposed development. The foundation system comprises rotary bored, cast in-situ concrete piles socketed into the rock below the tunnel; in addition a slip coating / system is incorporated around the pile shaft to tunnel invert level to prevent side loading of the tunnel walls. This proposal falls into foundation zone 2.1, and foundation type H (refer Fig A5.1), therefore the following information is likely to be required as a minimum (see cat C – fig. A5.1):-

• Scale plan and section of proposed development relative to the subway infrastructure • Structure type • Foundation type, level and loading • Construction methods proposed • Ground investigation establishing stratification of site and soil / rock classification and characteristics • Calculation of stress increase in the ground surrounding tunnels* • Calculation of Ground deformations * • Calculation of change in stress in tunnel lining and approximate tunnel deformation * * It is possible that the above calculations may not be required if a suitable slip coating / slip system is

incorporated, which is acceptable to SPT. It is likely that the suitability of the piling system, including the shaft slip mechanism, will need to be proven as acceptable to SPT by undertaking a test pile installation; this test pile arrangement shall include vibration monitoring, and possibly deformation monitoring, which will require to be installed inside the tunnels during night shift.

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guidance notes for developments or engineering works in the