Singapore Building and Construction Authority (Building Engineering Division)
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Singapore Building and Construction Authority (Building Engineering Division). Managing Geotechnical Risks – are we learning from our failures 29 th September 2006 Andy Pickles & Tom Henderson Geotechnical Consulting Group (Asia) Ltd. Contents.
Singapore Building and Construction Authority (Building Engineering Division)

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Slide 1

Singapore Building and Construction Authority(Building Engineering Division)

Managing Geotechnical Risks – are we learning from our failures

29th September 2006

Andy Pickles & Tom Henderson

Geotechnical Consulting Group (Asia) Ltd.

Asia

Slide 2

Contents

  • Overview of the management of geotechnical risk (Tom Henderson)

  • Overview of deep excavation practice in Hong Kong (Tom Henderson)

  • Comment on the scope and reporting of site investigations (Tom Henderson)

  • Design aspects for deep excavations and in particular the use of numerical modelling (Andy Pickles)

  • Instrumentation to verify design and control during construction of deep excavations (Andy Pickles)

  • Miscellaneous lesson learnt from the investigation into Nicoll Highway collapse (Andy Pickles)

Asia

Slide 3

Deep Excavation Practice in Hong Kong

Some general comments

  • Ground conditions issues in Hong Kong for deep excavations tend to be different to those encountered in Singapore

  • Deep excavations normally confined to shoreline

  • Presence of weathered rock and/or variable reclamation fill mean that sheet piles not commonly adopted for deep excavations of any significance

  • Support systems are fairly robust – but groundwater control often a concern

Asia

Slide 4

Statutory Control of Deep Excavation Design and Construction in Hong Kong

Covered by Building Ordinance and Building Regulations (Cap 123)

  • Statutes attempt to regulate the following:

    qualifications (competency) of the representatives for parties associated with design and construction

    design submissions for deep excavations

    construction supervision and performance review

Asia

Slide 5

Statutory Control of Deep Excavation Design and Construction in Hong Kong

Control of the parties involved

  • Building Authority maintains a list of the following who are qualified to participate in design and construction of deep excavation works in Hong Kong

    Authorized Person (AP)

    Structural engineers (RSE)

    Geotechnical engineers (RGE)

    Approved general contractors

    Approved specialist contractors

Asia

Slide 6

Statutory Control of Deep Excavation Design and Construction in Hong Kong

General Control

  • Building Authority operates on a two stage control system

    written approval of documents/plans submitted – design approval

    written consent to commence construction in accordance with approved plans + acceptable supervision plan – construction approval

    Approval has a 60 day assessment period and is valid for 2 years

    Consent has a 28 day assessment period and is valid for 3 months

    BA will normally request input from other Government departments in submission review process – CED, GEO, HyD, DSD

Asia

Slide 7

Statutory Control of Deep Excavation Design and Construction in Hong Kong

Approved Plans for Deep Excavation – Excavation and Lateral Support Plan

In addition to plans and sections showing arrangement and sequence of excavation and support – supporting documentation will normally include:

Assembly of all relevant factual information

geology, hydrogeology, site history, utilities

Interpretative report based on all factual data plus –

Discussion of anticipated geotechnical problems

Actions if geotechnical assumptions are found to be erroneous

Calculations on limiting stresses and movements in the support system

Instrumentation and monitoring plans

Asia

Slide 8

Statutory Control of Deep Excavation Design and Construction in Hong Kong

Site Supervision Plan

  • Recent addition to regulatory control

  • Amalgamation of quality management and safety management plans and supervision/reporting requirements for works with significant geotechnical content

  • Technical Memorandum – Building Regs

  • Code of Practice – guidance document

Asia

Slide 9

Statutory Control of Deep Excavation Design and Construction in Hong Kong

Site Supervision Plan

  • Pre-requisite for consent to commence construction

  • Principally a safety management tool

  • Establishes procedures to ensure works are constructed in compliance with Building Regs and approved plans

  • Implicitly – verify design assumptions relating to ground and ground water conditions during construction

Asia

Slide 10

Statutory Control of Deep Excavation Design and Construction in Hong Kong

Site Supervision Plan

  • Authors are named AP,RSE, RGE plus named representative from approved contractor's)

  • Identify/Characterize particular hazards associated with construction works and the means/personnel required to address them

  • Identify degree of supervision required and grade/experience of supervisory personnel

  • Identify critical tasks that are particular to the construction works

Asia

Slide 11

Statutory Control of Deep Excavation Design and Construction in Hong Kong

Approved Devolvement of Supervision Responsibility

  • Building Ordinance recognizes limitations of RGE presence on major works

  • Allows RGE to devolve responsibibility of supervision role to “technically competent person(s)” - TCP

  • TCP is a person with recognized academic & professional qualifications commensurate with supervision requirements

  • Building Ordinance recognizes 5 levels of TCP for supervision of construction works

Asia

Slide 12

Statutory Control of Deep Excavation Design and Construction in Hong Kong

Supervision required for Deep Excavations in Hong Kong

  • Classified as “building works with significant geotechnical content”

  • Requires as a minimum:

    Full-time presence of TCP (3) – degree holder + 2 years relevant experience

    Weekly Inspection by TCP (5) – degree holder + 5 years relevant experience

    Ad-hoc inspections by RGE

  • Supervision tasks generally address

    Engineering safety – requiring professional judgment – TCP 4/5

    Routine Safety – compliance with Ordinance/Codes – TCP 1-3

Asia

Slide 13

Statutory Control of Deep Excavation Design and Construction in Hong Kong

Reporting

  • Site Supervision Reports required whenever TCP/RGE are on site

    Full-time presence of TCP - Daily Reports

    Weekly Inspection by TCP – Weekly Reports

    Ad-hoc inspections by RGE – Periodical Reports

  • Format of Reports

    List of works inspected – results of inspection

    Notes of non-conformance – recommendations on remedies

Asia

Slide 14

Statutory Control of Deep Excavation Design and Construction in Hong Kong

Critical Tasks

  • RGE expected to identify “Critical Tasks” in Site Supervision Plan that will required increased levels of supervision

  • Excavation works close to water mains, gas mains, buildings on shallow footings, MTR/KCRC railways

  • Pre-loading of struts

  • Pumping tests

  • Attainment of founding levels for retaining walls

  • Removal of structural support in the absence of permamant support

  • All works when allowable movements groundwater changes have exceeded prescribed limits

Asia

Slide 15

Statutory Control of Deep Excavation Design and Construction in Hong Kong

Other Associated Documents for Reference

  • GEO Guide #1 “Guide to Retaining Wall Design”

  • GCO Publication #1/90 “Review of Design Method for Excavations”

  • GEO Report #56 “Application of Prescriptive Methods to Slopes and Retaining Walls

  • GEO Technical Guidance Notes

  • Works Branch Technical Circulars (WBTC 3/97 – requirement for ICE for retaining walls)

  • Practice Notes for Approved Persons (PNAP)

Asia

Slide 16

Statutory Control of Deep Excavation Design and Construction in Hong Kong

Summary

  • Well regulated and rigorous procedures for engineering profession

  • Recent changes in supervision/reporting of construction are for the better

  • TCP role reduces pressure on RGE as individual

  • Reasonably sensitive to variation in scale and complexity of works that are carried out

Asia

Slide 17

Thank you

Asia


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