environment, transport 環境運輸及工務局 and works bureau 香港 …

ETWB TCW No. 15/2005 of 10

政府總部

環境運輸及工務局香港花園道美利大廈

Environment, Transport and Works Bureau

Government Secretariat Murray Building, Garden Road,

Hong Kong

Ref. : ETWB(W) 925/52/01 Group : 5, 7

29 September 2005

Environment, Transport and Works Bureau Technical Circular (Works) No. 15/2005

Geotechnical Control for Tunnel Works

Scope This Circular outlines the policy and procedures for geotechnical control of planning, design and construction for tunnel works. The Director of Lands and the Director of Environmental Protection have agreed to this Circular. 2. Tunnel works comprise tunnels, shafts, caverns and associated underground facilities, however constructed. Construction of tunnel works may involve use of drill and blast methods, tunnel-boring machines, cut and cover methods, techniques that incorporate insitu ground treatment, groundwater control, installation of temporary and permanent supports, etc. Maintenance aspects of tunnels are not covered. Furthermore, the geotechnical control requirements do not apply to immersed tube tunnels, box culverts, submarine outfalls and underground pipes for drains, sewers and water mains. Effective Date 3. This Circular is applicable to projects involving tunnel works, for which the tender for the works is invited on or after 1 December 2005. However, there is no need to follow the requirements described in paragraphs 12 and/or 13 if the

香港特別行政區政府 The Government of the Hong Kong Special Administrative Region


feasibility study have already been completed and/or technical and fee proposals for the selection of consultants for the project have already been invited on the date of issue of this Circular. Effect on Existing Circular 4. This Circular should be read in conjunction with the following circulars:

Circular No. Subject

ETWB TCW No. 29/2002 Geotechnical Control for Slopes and Retaining Walls

ETWB TCW No. 29/2003 Confidentiality Clauses in Works Contracts and Consultancy Agreements

ETWB TCW No. 17/2004 Impossibility/Unforeseen Ground Conditions/Utility Interference

ETWB TCW No. 6/2005 Implementation of Systematic Risk Management in Public Works Projects

Background 5. A review carried out by the Environment, Transport and Works Bureau (ETWB) on the implementation issues of the Harbour Area Treatment Scheme (HATS) Stage I project has indicated the need to strengthen geotechnical input and control for future projects involving tunnel works. This includes the need to involve government’s in-house geotechnical expertise at appropriate stages of the project, especially in the early project planning and contract preparation stages, and in the interpretation, modelling and verification of ground conditions during the design and construction stages. Policy 6. The Project Department (PD) shall ensure that the documentation for the


geotechnical design of all permanent tunnel works and the associated temporary works is submitted to the Geotechnical Engineering Office (GEO) of the Civil Engineering and Development Department (CEDD) as set out in this Circular. The GEO shall audit the geotechnical design and the implementation of the geotechnical design, site supervision and risk management during construction, where the tunnel works or their construction would pose a significant risk to public life or property, and provide geotechnical advice to the PD. 7. The GEO’s audits do not change the authority, duties, responsibilities and liabilities of the PD and its agents (consultants/contractors) for the project/contract. Risk Assessment and Exemption from Audit 8. At the feasibility study stage of a project involving tunnel works, the PD shall conduct a risk assessment to determine whether the proposed tunnel works under the project would pose a significant risk to public life or property. Where the risk assessment shows that the risk to public life and property posed by any section of the tunnel works would be insignificant, such works are exempt from the audit requirements on the approval of an officer at D2 rank or above from the PD. For these exemption cases, the PD will not need to submit to the GEO for audit the geotechnical design of the tunnel works and associated documents, and GEO will not undertake site audits. Notwithstanding, the PD shall comply with all general requirements of this Circular, including the GEO consultation requirements (see paragraphs 12, 13, 17 and 18) and the requirements to make submissions to GEO for record purposes (see paragraph 25). When granting such approval, the approving officer of the PD shall take into account any major assumptions, in particular the geotechnical assumptions made in the risk assessment, and require verification of the assumptions and where necessary a review of the risk management at the design and construction stages. The PD shall submit a copy of the risk assessment to the Deputy Head (Mainland) of the GEO, CEDD for record. Submissions 9. All project-specific submissions shall be made to the Chief Geotechnical Engineer (CGE) of the relevant district division of GEO. (The boundaries of the GEO district divisions are shown in Figure 1 of ETWB TC(W) No. 29/2002). For major projects which straddle district boundaries, the GEO will provide a one-stop


service and nominate a district CGE as co-ordinator for processing all submissions (on the tunnel works as well as those required under ETWB TC(W) No. 29/2002 for any slopes and retaining walls forming part of the project). The PD shall make submissions to the GEO as early as possible, to facilitate contract preparation and project implementation. 10. The GEO will provide its response to a submission to the PD as quickly as possible and always within 28 calendar days of its receipt. Where a shorter response time is required, the PD and GEO should agree suitable arrangements for the submission. 11. The PD shall make due allowance in the project programme for the time required to make submissions to the GEO for consultation and audit under this Circular. Feasibility Study Stage Consultation 12. In accordance with FC No. 11/2001, the PD is required to include a preliminary geotechnical appraisal (PGA) of the project in the Technical Feasibility Statement (TFS). In preparing the PGA for the project and in undertaking any supporting engineering feasibility studies (EFS), the PD or its consultants shall consult the Hong Kong Geological Survey through CGE/Planning of the GEO to obtain general geological advice, especially on identification of geological features. The EFS and the PGA of the project should cover geotechnical considerations such as identification of problematic ground, formulation of preliminary ground models including the hydrogeological models, and preliminary assessment of geotechnical risks (both during construction and in the long-term when the facility is operating). They should also cover the possible scope and extent of site investigations and geotechnical studies required to reduce uncertainties and risks. The PD shall consult the GEO, take into account GEO’s response in finalising these documents and submit a copy of the final versions to the GEO. Consultation During Preparation of Consultancy Briefs 13. The PD shall include provisions in the consultancy briefs for design and construction of tunnel projects to incorporate the GEO consultation and submission requirements under this Circular. The PD shall consult the GEO on the briefs, take


into account GEO’s response in finalising the briefs and submit a copy of the final versions to the GEO. Engineer’s Designs – Detailed Design Stage Submission 14. The PD or its consultants shall submit to the GEO for audit the documentation on the geotechnical design of all tunnel works and any associated temporary works undertaken by them (i.e. Engineer’s design), where such works would pose a significant risk to public life or property. Details of the information to be included in the geotechnical design submission are given in Appendix A. The geotechnical issues identified in the EFS and the PGA, as well as any comments provided by the GEO in the feasibility study stage, shall be addressed in the submission. The PD or its consultants shall also review the validity of the original assumptions made and if necessary update the risk assessment, taking into account all additional geotechnical and other relevant site data collected, any on-going works in the vicinity of the site, the Engineer’s design and the stipulated/assumed construction methods and procedures (see paragraph 8). They shall submit to GEO a copy of any updated risk assessment carried out if this indicates any sections of tunnel works, additional to those previously identified, would pose a significant risk to public life or property. The PD or its consultants shall also make a geotechnical design submission related to such works to the GEO for audit. 15. The geotechnical design submission shall identify the requirements for any investigation, geological/hydrogeological mapping (see paragraph 26), design/design review, inspection, testing, survey/monitoring, supervision of built quality, risk assessment and management, geotechnical performance review, and documentation and reporting that the PD or its consultants are required to carry out during the implementation of the works contract. Contract Preparation Stage and Tendering 16. The PD shall include suitable clauses in the Particular Specifications (PS), and, in the case of Design and Build (D&B) contracts, the Employer’s Requirements (ER), to enable effective implementation of this Circular. The clauses should:


(a) incorporate requirements that take account of comments made by GEO on

the feasibility study stage submissions and, for Engineer’s design projects, the detailed design stage submissions;

(b) specify that copies of all documents, records and other information related to the design and construction of the tunnel works under the contract, including those prepared or obtained by the Engineer/Architect/Supervising Officer (E/A/SO) and the Contractor, may be submitted or provided to the GEO; and

(c) include requirements on any investigation, geological/hydrogeological mapping (see paragraph 26), design/design review, inspection, testing, survey/monitoring, supervision of built quality, risk assessment and management, geotechnical performance review, and documentation and reporting that the Contractor is required to carry out under the contract.

In addition, where a marking scheme is used for tender evaluation, the marking scheme for the tenderers’ technical submissions should contain elements and due weight for assessment against the minimum requirements governing the competence and experience of site supervision staff, including geotechnical/tunnelling/blasting specialists, that the Contractor is required to employ under the contract. 17. Where blasting works are anticipated, the PD or its consultants shall consult CGE/Mines, GEO, CEDD as early as possible regarding the issues related to the site storage, delivery and use of explosives that need to be considered. The issues shall be properly addressed prior to tendering of the contract. 18. The PD or its consultants shall consult the GEO on the PS or the ER clauses related to the tunnel works and any associated temporary works, take into account GEO’s response in finalising the clauses and submit a copy of the final clauses to the GEO. The PD shall consult the GEO on the minimum requirements on the site supervision personnel that the E/A/SO shall employ for supervising the various items of work identified including that in paragraph 15. They shall also consult the GEO on the minimum requirements on the site supervision personnel that the Contractor shall employ under the contract for supervising the various items of work identified in paragraph 16(c). The GEO shall advise on the minimum requirements for the supervision of construction of the different types of tunnel works under the contract. The PD shall take into account GEO’s response and request its consultants to take appropriate action, and submit a copy of the final site supervision requirements to the GEO.


19. Where the GEO raises major geotechnical concerns on the public safety aspects of the geotechnical design or the related PS or the ER clauses, the PD must resolve such concerns before tenders are invited. Any unresolved major issues shall be promptly brought to the attention of the directorate officers in the PD and GEO for a speedy resolution. Construction Stage Submissions 20. After the award of the contract but prior to the commencement of construction of the tunnel works, the PD or its consultants shall submit the following documents to the GEO in relation to those sections of tunnel works that would pose a significant risk to public life or property:

(a) the contract programme; (b) the Contractor’s proposed construction methods and procedures; (c) where Contractor’s design is involved, details of any risk assessment with

respect to risk to public life and property and any geotechnical design prepared by the Contractor, after any detailed checking and certification required under the contract (see Appendix A for details of geotechnical design submission required); and

(d) details of the E/A/SO’s and the Contractor’s actual site supervision arrangement and management structure, including the curriculum vitae of the key site supervision personnel, and their duties, responsibilities, authority and lines of reporting (see Appendix A).

The PD or its consultants shall also submit updated versions of the above documents to the GEO should there be significant amendments before or during construction of the tunnel works, as soon as they become available. 21. For any Engineer’s designs of tunnel works and associated temporary works under the contract, the PD or its consultants shall review the validity of the original assumptions made and if necessary update the risk assessment previously carried out (see paragraph 14), taking into account all additional geotechnical and other relevant site data collected during the contract, any on-going works in the vicinity of the site, and the Contractor’s proposed construction methods and procedures. The PD or its consultants shall submit to GEO a copy of any updated risk assessment carried out if this indicates any sections of tunnel works, additional to


those previously identified, would pose a significant risk to public life or property. The PD or its consultants shall also make a geotechnical design submission related to such works, together with any updated versions of the Engineer’s designs for the sections of tunnel works the construction of which have previously been assessed as posing a significant risk to public life or property, to the GEO. The submissions shall be made prior to commencement of construction of the related section of the works. 22. GEO may audit the documents submitted and carry out site audits. The E/A/SO shall make suitable arrangements, make available to the GEO during the site audits all records and other information related to the consultancy/contract, and provide all assistance required by the GEO to facilitate these audits. 23. The GEO will submit its audit reports to an officer at D1 rank or above in the PD managing the project, who shall study critically the audit findings and take necessary follow-up actions in a timely manner. For cases where GEO considers that continuing the works would pose significant risk to public life and property, the GEO should immediately bring the matter to the attention of the E/A/SO and the relevant directorate officer of the PD for follow-up action. Submission Prior to Consultancy/Contract Completion 24. For all tunnel works, the PD or its consultants shall submit the following to the GEO for record prior to the completion of any consultancy/contract under the project, as appropriate:

(a) the geotechnical performance review carried out and monitoring/survey data obtained for the tunnel works (prepared by the designer and certified by the design checker);

(b) the geological and hydrogeological data collected including any field data obtained from the excavation faces (see paragraph 26);

(c) as-built survey plans (accepted by the E/A/SO under the contract) showing the boundaries of the tunnels/shafts/caverns and the extent of any temporary works which may affect future construction; and

(d) maintenance manuals, where appropriate, for the maintenance and the long-term monitoring of special measures such as prestressed ground anchors (prepared by the designer and certified by the design checker).


For those sections of tunnel works for which the geotechnical design is exempt from the GEO audit requirements, the PD shall submit to the GEO for record the documentation on the geotechnical design (including any significant amendments) and any risk assessment with respect to risk to public life and property carried out during design or construction. The PD shall submit these documents either individually at the stage of the project when each final/certified document becomes available, or all together in a single package prior to completion of the consultancy/contract. Technical Guidance 25. Technical guidance on geotechnical aspects of tunnel works will be prepared from time to time in the form of GEO Technical Guidance Notes, which are accessible through the CEDD website http://www.cedd.gov.hk. Annex TGN1A1 of Technical Guidance Note (TGN) No. 1 lists the guidance documents being used by the GEO as de facto geotechnical standards. The TGN can be found at the CEDD website. Documentation and Submission of Geological and Hydrogeological Data 26. The E/A/SO shall ensure the factual geological and hydrogeological data, such as field data collected from the excavation faces and monitoring data, obtained during construction of the tunnel works under the contract are properly documented. The consultancies and the works contracts involving tunnel works shall specify that competent personnel with relevant qualifications and experience shall be employed to collect, document and certify the accuracy of such data. The PD shall submit the data to the Public Section of the Geotechnical Information Unit, CEDD in accordance with WBTC No. 20/2001. The Hong Kong Geological Survey will refer to such data when preparing new or revised geological maps. Advisory Services 27. For general geological advice, the PD shall consult the Hong Kong Geological Survey through CGE/Planning of the GEO.


28. The GEO also operates a geotechnical engineering advisory service to assist government departments with the geotechnical aspects of their projects. These could include the identification and resolution of geotechnical problems, planning and interpretation of site investigation, ground modelling, and preparation of geotechnical submissions for their projects. Requests for geotechnical advice/assistance, including that on the engineering feasibility study, investigation, design, assessment of impacts due to proposed tunnel works, assessment of impacts on existing tunnels due to other proposed projects, and maintenance of existing cavern and tunnel facilities, if required, should be directed to CGE/Geotechnical Projects of the GEO. This service does not obviate the need for the PD to make submissions to the GEO for audit/record as required under this Circular. 29. Any further queries on this Circular or related issues should be directed to PAS(W)3 of this Bureau.

( C S Wai ) Deputy Secretary for the Environment,

Transport and Works (Works) 2

ETWB TCW No. 15/2005 Appendix A Page A1 of 2

Appendix A

Geotechnical Design Submission for Tunnel Works The geotechnical design submission for tunnel works shall include plans, reports and specifications covering the following aspects:

(a) plans showing the details of the permanent tunnel works and the associated temporary works and the works contract boundary;

(b) assumptions and, where applicable, any requirements to be specified in the contract on construction methods and procedures;

(c) the design and geotechnical risk assessment approach, e.g. analytical/empirical approach and the Observational Method;

(d) standards and principles;

(e) supporting site investigation data and geotechnical studies;

(f) an assessment of the adequacy and reliability of the data used to formulate the ground model, including hydrogeological model, for the geotechnical design and the geotechnical risk assessment, and the geotechnical assumptions;

(g) design calculations including assessment of earth pressures and water pressures, stability analysis and sensitivity analysis;

(h) an assessment of the magnitude and extent of ground settlement/heave/lateral movement, including estimates of the maximum allowable water inflow rates/groundwater pressure changes to be specified in the contract for the control of ground deformation, as well as their effects;

(i) an assessment of construction-induced vibrations and their effects;

(j) an assessment of the pre-construction conditions and vulnerability of other properties/facilities that could be affected by the works, e.g. buildings, roads, slopes, landfills, tunnels and utilities, and of the exposure of members of the public;

(k) if blasting is anticipated, a blasting assessment to demonstrate that the effects of blasting works on adjacent built properties/facilities, including geotechnical features and members of the public, are within acceptable limits, and documentation of the basis for estimating the tunnel advance rates, taking into account the allowable charge weights;

(l) plans, reports and specifications giving the details of the safety-critical plant and equipment (e.g. TBM) and the preventive and mitigation measures required, and a report documenting the performance monitoring and design review system designed to check the performance of the tunnel works and

ETWB TCW No. 15/2005 Appendix A Page A2 of 2

to verify the design assumptions and the adequacy of the construction methods/procedures and preventive/mitigation measures throughout construction of the works, including limits for alerting the designer to carry out review and for suspending the works of the Contractor, and their basis, and the associated contingency measures in the event that the set limits are exceeded; and

(m) plans, reports and specifications giving the details of the reinstatement works where these would pose geotechnical risks affecting public life or property, e.g. backfilling of access shafts and removal of temporary supports.

Notes: A site supervision plan incorporating the following shall be provided to the

GEO prior to commencement of construction of the related section of tunnel works:

(1) the site supervision arrangement and management structure, clearly identifying the parties responsible for making key assessments/decisions and taking action relating to the design, built quality and risk management of the temporary and permanent tunnel works;

(2) the curricula vitae of key site supervision personnel to confirm that the PD or its consultants (for consultant-supervised contracts) and the Contractor have employed site supervision staff with relevant qualifications and experience to identify and supervise all items of work identified in the geotechnical design submission to be requiring supervision, their duties, responsibilities, authority and lines of reporting under the consultancy (for consultant-supervised contracts) and works contract;

(3) if blasting works are anticipated, the curricula vitae of key site supervisions personnel to confirm that the PD or its consultants (for consultant-supervised contracts) and the Contractor have employed site supervision personnel with relevant qualifications and experience to check and/or approve the blast designs, method statements, blasting assessments and other submissions related to any blasting works to be carried out, and to supervise the carrying out and safety of such works under the contract; and

(4) the standard of service required of the site supervision staff (e.g. full-time, or the frequency/time of inspection/check/design review if part-time), and the names of clearly identified individuals responsible for checking and certifying all critical items and procedures prior to construction of the temporary and permanent tunnel works, and for timely documentation and checking/review of all observations, interpretations, decisions and actions taken.

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