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.
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Contents
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Overview of the management of geotechnical risk (Tom Henderson)
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Overview of deep excavation practice in Hong Kong (Tom Henderson)
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Comment on the scope and reporting of site investigations (Tom Henderson)
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Design aspects for deep excavations and in particular the use of numerical
modelling (Andy Pickles)
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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)
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Deep Excavation Practice in Hong Kong
Some general comments
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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
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Statutory Control of Deep Excavation Design and
Construction in Hong Kong
Covered by Building Ordinance and Building Regulations
(Cap 123)
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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
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Statutory Control of Deep Excavation Design and
Construction in Hong Kong
Control of the parties involved
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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
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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
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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
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Statutory Control of Deep Excavation Design and Construction in
Hong Kong
Site Supervision Plan
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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
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Statutory Control of Deep Excavation Design and Construction in
Hong Kong
Site Supervision Plan
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Pre-requisite for consent to commence construction
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Principally a safety management tool
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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
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Statutory Control of Deep Excavation Design and Construction in
Hong Kong
Site Supervision Plan
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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
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Statutory Control of Deep Excavation Design and Construction in
Hong Kong
Approved Devolvement of Supervision Responsibility
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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
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Statutory Control of Deep Excavation Design and Construction in
Hong Kong
Supervision required for Deep Excavations in Hong Kong
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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
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Statutory Control of Deep Excavation Design and Construction in
Hong Kong
Reporting
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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
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Format of Reports
List of works inspected – results of inspection
Notes of non-conformance – recommendations on remedies
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Statutory Control of Deep Excavation Design and Construction in
Hong Kong
Critical Tasks
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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
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Pre-loading of struts
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Pumping tests
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Attainment of founding levels for retaining walls
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Removal of structural support in the absence of permamant support
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All works when allowable movements groundwater changes have exceeded
prescribed limits
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Statutory Control of Deep Excavation Design and Construction in
Hong Kong
Other Associated Documents for Reference
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GEO Guide #1 “Guide to Retaining Wall Design”
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GCO Publication #1/90 “Review of Design Method for Excavations”
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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)
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Statutory Control of Deep Excavation Design and Construction in
Hong Kong
Summary
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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
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Thank you
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