1. 1 Asia Managing Geotechnical Risk Are we learning from the failures “ The Use of Instrumentation and Monitoring to Verify Design and Control Construction of Deep Excavations (modified)” Andy Pickles of GCG (Asia) Ltd.

2. 2 Asia Overview of Presentation Presentation relates to deep excavation for major infrastructure projects Risk in design and role of instrumentation Risk in design and role of instrumentation Typical scope and cost of instrumentation Typical scope and cost of instrumentation Obtaining added value (reducing risk) from instrumentation Obtaining added value (reducing risk) from instrumentation Interpretation of instrumentation Interpretation of instrumentation

3. 3 Asia Risk in Design of Deep Excavations Instrumentation is associated with the management of risk (i.e. uncertainties). These include: Soil stratigraphy Soil stratigraphy Geotechnical design parameters Geotechnical design parameters Construction related factors Construction related factors

4. 4 Asia Uncertainty of Soil Stratigraphy Variation of Continuity of Sand Layer Discontinuous LayerContinuous Layer

5. 5 Asia Uncertainty in Design Parameters - 1 Deep Excavation in Clay FILL Soft CLAY Stiff CLAY Clayey SAND Hard CLAY 75 40 Bend Mom 2800 kNm 5000 kNm

6. 6 Asia Uncertainties in Design Parameters – 2 Variation of Rate of Softening Low PermeabilityHigh Permeability

7. 7 Asia Construction Related Uncertainties -1 Performance of Grout Cut-off CLAY

8. 8 Asia Construction Related Uncertainties - 2 Ground settlement on wall installation Ground settlement on wall installation Effectiveness and extent of dewatering Effectiveness and extent of dewatering Properties of jet grout layers Properties of jet grout layers Effectiveness of ground treatment Effectiveness of ground treatment Effects of previous construction work Effects of previous construction work Interaction with adjacent structures Interaction with adjacent structures

9. 9 Asia Instrumentation to deal with these risks All design approaches All design approaches Design parameters from previous experience Determined from instrumentation results Routine design approach Routine design approach Offset risk by using conservative assumptions Verify design using instrumentation results (AAA) Observational approach (progressive modification) Observational approach (progressive modification) Manage risk through engineering input Less conservative assumptions Continuous improvement of design based on instrumentation results As knowledge improves design improves and risk remains constant.

10. 10 Asia Trigger Levels in Routine Design Trigger levels are used as part of the AAA system Trigger levels are used as part of the AAA system Important to distinguish between trigger levels set using the design predictions, on the basis of additional calculation and based on engineering judgement Important to distinguish between trigger levels set using the design predictions, on the basis of additional calculation and based on engineering judgement Design predictions are unreliable and AAA value requires a design review, if appropriate AAA values can be updated Design predictions are unreliable and AAA value requires a design review, if appropriate AAA values can be updated Additional calculation is based on actual serviceability and AAA values should not be exceeded Additional calculation is based on actual serviceability and AAA values should not be exceeded Engineering judgement are often guesses or best practice and more detailed analysis is then required and AAA values can be revised Engineering judgement are often guesses or best practice and more detailed analysis is then required and AAA values can be revised

11. 11 Asia Managing Risk and Obtaining Value If the major role of instrumentation is to manage risk how can we make it more effective? If the major role of instrumentation is to manage risk how can we make it more effective? Alternatively, how can we get more value out of instrumentation? Alternatively, how can we get more value out of instrumentation?

12. 12 Asia The Role of Instrumentation Routine design and construction Routine design and construction To verify an already conservative design Observational approach Observational approach Use data to continually improve design Reduce construction costs Save construction time Long term perspective Long term perspective Full interpretation published with all background information allows future designs to be improved Benefits accrued by major clients 0% 10% INCREASINGVALUEINCREASINGVALUE

13. 13 Asia Typical Scope of Standard Instrumentation Standard instrument type 1 km cut and cover with station in Singapore 1 km cut and cover with station in Hong Kong Inclinometers in walls 12050 Strut load monitoring 400200 Piezometers (VW and standpipe) 50120 Settlement points 800500 Extensometers1015

14. 14 Asia Scope of Data Collection Typically 1000 to 2000 separate instruments Typically 1000 to 2000 separate instruments Readings required daily during excavation and strut removal stages and weekly at other times Readings required daily during excavation and strut removal stages and weekly at other times Typically of the order of 200 readings per instrument Typically of the order of 200 readings per instrument 400,000 separate sets of readings 400,000 separate sets of readings 1,000,000 or more data points 1,000,000 or more data points

15. 15 Asia Typical cost of instrumentation Cost includes Instrumentation Instrumentation Monitoring teams (instrumentation and survey) Monitoring teams (instrumentation and survey) Engineering support to coordinate work Engineering support to coordinate work Development and maintenance of database Development and maintenance of database Daily, weekly and monthly reporting with associated meeting costs Daily, weekly and monthly reporting with associated meeting costs Cost of instrumentation and monitoring 1.5% to 2% of contract value Management cost (engineering support, meetings etc.) 0.5% to 1% of contract value Total cost 2% to 3% of contract value

16. 16 Asia Cost of Instrumentation Routine Design Total cost for routine instrumentation of a deep excavation contract is S$ 5 to 10 million Total cost for routine instrumentation of a deep excavation contract is S$ 5 to 10 million Primary use is to verify the design of the excavation works Primary use is to verify the design of the excavation works Cost is of similar order to the original design costs (i.e. pay as much to verify as to design) Cost is of similar order to the original design costs (i.e. pay as much to verify as to design) Instrumentation is often seen as an onerous contract requirement Instrumentation is often seen as an onerous contract requirement No added value obtained from instrumentation No added value obtained from instrumentation Designer is often not closely involved with construction Designer is often not closely involved with construction

17. 17 Asia How to Add Value to Instrumentation Adding value is reducing risk and reducing cost Adding value is reducing risk and reducing cost Involve designer in the construction work Involve designer in the construction work Prepare good quality instrumentation interpretative reports (comprehensive rather than instrument specific) Prepare good quality instrumentation interpretative reports (comprehensive rather than instrument specific) Carry out back analyses to determine actual performance parameters Carry out back analyses to determine actual performance parameters Encourage value engineering through observational approach Encourage value engineering through observational approach Publish results and improve standards and codes of practice Publish results and improve standards and codes of practice

18. 18 Asia Cost of Adding Value to Instrumentation Additional cost for proper interpretation of results and associated report is S$ 0.1 million Additional cost for proper interpretation of results and associated report is S$ 0.1 million Additional cost for back analysis in order to obtain useful design data for future work is S$ 0.1 to 0.2 million Additional cost for back analysis in order to obtain useful design data for future work is S$ 0.1 to 0.2 million Large savings in Contract costs and times are achievable by making better use of monitoring data Large savings in Contract costs and times are achievable by making better use of monitoring data Additional costs can usually be offset by better control of day to day monitoring (i.e. cut down frequency) Additional costs can usually be offset by better control of day to day monitoring (i.e. cut down frequency)

19. 19 Asia Examples of Excessive Monitoring Manual Settlement Readings -15 -5 -120 0 Jan 00 Nov 01

20. 20 Asia Examples of Excessive Monitoring Manual Piezometer Readings 3 2 1 0 Groundwater Level mPD 18 Months with 500 Measurements

21. 21 Asia Examples of Excessive Monitoring Datalog Piezometer Readings 2 1 0 Groundwater Level mPD 1 Day Piezometer Tide Gauge

22. 22 Asia Examples of Excessive Monitoring Datalogged Piezometer Readings 2.5 -15 -5 Jan 00 Nov 01 -1.5

23. 23 Asia Monitoring Frequency, Value and Risk My experience approximately 50% of monitoring is unnecessary. My experience approximately 50% of monitoring is unnecessary. Obtained because nobody is reviewing the data. Obtained because nobody is reviewing the data. Extra value can be obtained without additional cost by better control of instrumentation Extra value can be obtained without additional cost by better control of instrumentation Better value is associated with reduced risk Better value is associated with reduced risk Additional value can be obtained through Additional value can be obtained through Use of Observational Approach (Progressive Modification) Adoption of updated design codes (e.g. CIRIA C580) Feeding back information to future contracts

24. 24 Asia Proposal for Increasing Value of Instrumentation Use of Observational Method can achieve substantial cost savings and more importantly time savings (e.g. Powderham, Nicolson) Use of Observational Method can achieve substantial cost savings and more importantly time savings (e.g. Powderham, Nicolson) Adoption of CIRIA C580 which makes more use of instrumentation and can reduce cost of Dwalls by approximately 5% (Sze and Chan 2005) Adoption of CIRIA C580 which makes more use of instrumentation and can reduce cost of Dwalls by approximately 5% (Sze and Chan 2005) Scope for reducing factor of safety or load factor by 10% Scope for reducing factor of safety or load factor by 10% Paper to ICDE 2006 proposes adoption of C580 with improved instrumentation as an interim measure. Better use of instrumentation, involvement of designer and more widespread adoption of Observational Approach. Paper to ICDE 2006 proposes adoption of C580 with improved instrumentation as an interim measure. Better use of instrumentation, involvement of designer and more widespread adoption of Observational Approach.

25. 25 Asia Comment on Interpretation of Instrumentation The 4 Basic Steps 1. Baseline readings and background trends must be established (daily rainfall, seasonal rainfall, tide, temperature etc.) 2. Construction records are critical to data interpretation 3. Instrumentation results must be correlated against baseline trends and construction history 4. Analysis and presentation of data must consider cause and effect

26. 26 Asia Establish Baseline Trend “X”“X” “Y”“Y” Movement of Viaduct Structure 40 m Alert = 10 mm Action = 15 mm Alarm = 20 mm Maximum Allowable Water Drawdown Is 1m

27. 27 Asia Establish Baseline Trend – 1 Movement of Bypass Pier Head 50 -30 20 0 Jun 00 Oct 01 X-dir Y-dir July 00 Feb 01 40 mm 18 mm

28. 28 Asia Establish Baseline Trend – 1 Movement of Bypass 50 -30 20 0 Jun 00 Oct 01 X-dir Y-dir July 00July 01 40 mm 18 mm

29. 29 Asia Establish Baseline Trend – 2 Variation of Groundwater Level 0 1 2 3 Groundwater Level mPD Jan 00July 00 Jan 01July 01

30. 30 Asia Construction Records – Tabulated Data Pile No.Cap MarkInclination Drilling Start Date Drilling Completion Date Ground Level Casing Top Level (for R.H.) Length of Casing (mPD) (m) MP33A-1 MP33A 1:414-Jul-05 6.8007.06021.66 MP33A-21:426-Jul-05 6.8007.119 21.60 MP33A-31:403-Aug-0504-Aug-056.8007.030 21.54 MP33A-40:122-Aug-0523-Aug-056.8007.000 20.13 MP33A-51:405-Sep-0506-Sep-056.8007.037 20.45 MP33A-61:418-Jul-0519-Jul-056.8006.942 20.53 MP33A-71:409-Aug-0517-Aug-056.8006.892 20.15 MP33A-81:427-Jul-05 6.8007.104 20.97 MP33A-91:402-Aug-0503-Aug-056.8007.151 20.94 MP33A-101:416-Jul-05 6.8006.98920.94 MP33A-110:105-Sep-05 6.8007.05119.9 MP33A-121:4 15-Jul-05 6.8007.028 20.32 MP33A-131:408-Aug-0509-Aug-056.8007.015 20.21 MP33A-141:429-Aug-0530-Aug-056.8006.88419.78

31. 31 Asia Construction Records - Environmental

32. 32 Asia Construction Records – Progress Summaries

33. 33 Asia Construction Records - Photographs 3 March 2002

34. 34 Asia Correlate Response to Construction Activities Cause and Effect Plots Excavation level (mPD) Settlement (mm) Inclinometer (mm) Piezometer (mPD) -15 -5 -120 0 50 +2.5 -1.5 Jan 00 Nov 01

35. 35 Asia Correlate Response to Construction Activities and Baseline Trends -2 0 +1 +2 Jan 00July 00 Jan 01July 01 Tidal Response Start Dewatering Complete Dwall Stop Dewatering Rainfall Control Groundwater Level mPD

36. 36 Asia Summary The primary purpose of instrumentation is to manage risk The primary purpose of instrumentation is to manage risk Risk arises due to uncertainties in ground engineering Risk arises due to uncertainties in ground engineering Designer is aware of uncertainties so should be involved in construction (i.e. continuity) but is often excluded Designer is aware of uncertainties so should be involved in construction (i.e. continuity) but is often excluded Much instrumentation is wasted, not enough engineering input Much instrumentation is wasted, not enough engineering input Reduced costs and reduced risk (i.e. added value) can be obtained by better use of instrumentation Reduced costs and reduced risk (i.e. added value) can be obtained by better use of instrumentation Requires good quality interpretation of data and reporting to manage the risks Requires good quality interpretation of data and reporting to manage the risks

37. 37 Asia End of Presentation Thank you