GUIDANCE NOTES FOR DEVELOPMENTS OR ENGINEERING WORKS IN THE VICINITY OF SPT SUBWAY INFRASTRUCTURE JULY 2005

Transcription

1 GUIDANCE NOTES FOR DEVELOPMENTS OR ENGINEERING WORKS IN THE VICINITY OF SPT SUBWAY INFRASTRUCTURE JULY 2005

2 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 - 2 -

3 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

4 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

5 3.0 SPT APPROACH TO DEALING WITH APPLICATIONS FOR DEVELOPMENTS / WORKS IN THE VICINITY OF ITS SUBWAY INFRASTRUCTURE 3.1 General 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 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 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 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

6 3.2 Costs All cost associated with satisfying SPT requirements will be borne by the developer 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 Timescales 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 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

7 4.0 EXISTING SUBWAY INFRASTRUCTURE 4.1 General SPT Subway Infrastructure comprises a circular layout of twin tunnels, 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 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 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 Approximate tunnel levels can be obtained for site specific proposals from SPT

8 4.4 Tunnel Construction 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

9 5.0 INFORMATION SUBMISSION TO SPT 5.1 General 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 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 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 An initial guide to additional SPT information requirements, with respect to foundation proximity and foundation type / loading are given in Appendix

10 5.2 Further details in relation to points 3-7 above are given below: Detailed Site Ground Conditions 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 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 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 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 Detailed Information on Development Proposals 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

11 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 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 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 For lightly loaded foundations, remote from the Subway Infrastructure, simple analytical methods may be used 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

12 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 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 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 It should be noted that SPT is not liable for any costs associated with the assessment or provision of such measures

13 6.0 CRITERIA USED TO ASSESS DEVELOPMENT PROPOSALS 6.1 General 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 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 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 However as noted above, each development is considered by SPT on a case by case basis and exceptions to the above will occur

14 7.0 MITIGATING MEASURES 7.1 General 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 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 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 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

15 8.0 POSSIBLE CONSTRAINTS/RESTRICTIONS ON DEVELOPMENTS 8.1 Prior to Construction To minimise disruption, the time required for the activities associated with interfacing with the SPT, should be included in the development programme 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 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 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 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 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 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

16 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 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 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

17 9.0 SPT CONTACT INFORMATION 9.1 For further information, please contact :- Engineering SPT Glasgow Subway Broomloan Depot Robert Street GLASGOW G51 3HB Telephone No :

18 10.0 REFERENCES 10.1 Paper titled Centenary of the Glasgow Subway by JS Shipway `Proceedings of the Institution of Civil Engineers; Civil Engineering, 1996, 114, Aug Special Requirements and Specifications for Working in Tunnels Available from SPT on request

19 11.0 APPENDICES 11.1 Appendix 1 Plan of Subway indicating approximate location Appendix 2 Table indicating approximate minimum and maximum depths to crown of tunnels 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

20 APPENDIX 1 PLAN OF SUBWAY INDICATING APPROXIMATE LOCATION.

21 APPENDIX 1 N Hillhead Kelvinbridge Kelvinhall St. George s Cross Partick Cowcaddens Extent of Buffer Area Govan Buchanan St St. Enoch Ibrox Bridge St Cessnock Kinning Park Shields Rd Crown copyright and database rights 2014 Ordnance Survey Subway Consultation Zone Scale A2 West St Contact SPT if you are thinking about carrying out any demolition, development, site investigation or utility works within the yellow shaded area marked.

22 APPENDIX 2 TABLE INDICATING APPROXIMATE MINIMUM AND MAXIMUM DEPTH TO CROWN OF TUNNELS

23 DEPTH OF COVER TO SUBWAY TUNNELS Stations Minimum (m) Maximum (m) Kelvinbridge to St Georges Cross St Georges Cross to Cowcaddens Cowcaddens to Buchanan St Buchanan St to St Enoch St Enoch to Bridge St Bridge St to West St West St to Shields Rd Shields Rd to Kinning Park Kinning Park to Cessnock Cessnock to Ibrox Ibrox to Govan Govan to Partick Partick to Kelvinhall Kelvinhall to Hillhead Hillhead to Kelvinbridge (Mid Point)

24 APPENDIX 3 PLAN OF SUBWAY INDICATING APPROXIMATE EXTENT OF CONSTRUCTION TYPES

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26 APPENDIX 4 TYPICAL SECTIONS THROUGH THE VARIOUS TUNNEL CONSTRUCTION TYPES

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29 APPENDIX 5 SIMPLIFIED ZONING DIAGRAM INDICATING LIKELY SPT INFORMATION REQUIREMENTS

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31 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/m 2. 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/m 2. 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.