Singapore Building and Construction Authority (Building Engineering Division)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

17. Thank you Asia