Pile Acceptance A System View

Transcription

1 Pile Acceptance A System View AGS Perth, WA 12 May, 2015 Dr. Julian Seidel

2 Paper #1 Overview of The Role of Testing and Monitoring in the Verification of Driven Pile Foundations ANZ 2015 Wellington, NZ February, 2015 Dr. Julian Seidel

3 Talk Outline 1 st Paper Overview of Testing Static testing Dynamic testing 2 nd Paper Enhanced Use of PDA Dynamic Formulas (ECM) Pile Acceptance

4 1 Introduction > What is a system view? I care about the reliability of the single static or PDA test But I am more concerned about ensuring all 160 piles are OK My mind set is always how can I ensure intent is met for all piles?

5 Reconciling Test and System Perspectives Heirarchy of Test Reliability 1. Static Testing 2. PDA Testing 3. Dynamic Formulas Heirarchy of Project Influence 1. Dynamic Formulas 2. PDA Testing 3. Static Testing Inopiles International Pte Ltd

6 Static Load Testing the good, the bad and the ugly

7 1 Introduction > The reliability of design Pile design is uncertain prediction exercises typically show a range of 3 to 5 highest to lowest Testing is necessary because of unreliability of ground and stratigraphic variations

8 2 Pile Testing > 2.1 Static Load Testing > Load Measurement Static pile test : load measurement Static testing is the golden reference for pile testing IF PERFORMED TO A HIGH STANDARD Use of manometers rather than load cells can lead to capacity overestimates of 20% or more

9 2 Pile Testing > 2.1 Static Load Testing > Capacity Interpretation Static pile test capacity interpretation There is usually no definitive and unequivocal interpretation of a static load test In this typical example, the different interpretation methods lead to a 25% range of interpreted 'static capacity'

10 2 Pile Testing > 2.1 Static Load Testing > Capacity Mobilization and Proof Tests Mobilization : Proof vs Failure Tests If piles are tested to a proof load rather than geotechnical failure, then the actual capacity can only be inferred If the ultimate capacity is uncertain, then the static test is not a certain basis for developing a capacityset relationship

11 2 Pile Testing > 2.1 Static Load Testing > Low Statistical Representation Extrapolation of static testing highway bridge 96 pier bridge over flood plain 25m spans 16 piles/pier 0.5% = 1 pile every 12 spans or 300m 1% = 1 pile every 6 spans or 150m

12 2 Pile Testing > 2.1 Static Load Testing > Low Statistical Representation Capacity variations and testing frequency In this example, capacities in a single pier (5m x 12.6m) vary by 15% about the average (all toes within 0.2m penetration) How can the results of static pile tests be extrapolated distances of 150 to 300m? 1.8m

13 Capacity [kn] 2 Pile Testing > 2.1 Static Load Testing > Time dependent capacity changes The importance of time dependency Acceptance based on capacity, energy, set, TC at end of drive Static capacity at time of test may be more or less than the end of drive capacity, so a relationship with set, TC is misleading 2,500 2,000 1,500 1, capacity vs time end of drive capacity static capacity Time [days]

14 2 Pile Testing > 2.1 Static Load Testing > Time dependent capacity changes How to meaningfully use static? Basic problem : we need to control the DRIVING response of piles based on results of tests conducted weeks after driving. o o Static test to failure Use load cells to accurately measure capacity o Adopt a 'reasonable' and consistent ultimate capacity interpretation probably displacement based o Recognize and accommodate time-dependency Correlate static and dynamic tests Establish setup or relaxation quantum and variability

15 PDA Testing the good, the bad and the ugly

16 1 Introduction > How can PDA help? 1. Primarily it can be done extensively and spread around the site 2. But also it can be done at different times (EOID, Restrike) 3. It can be correlated UP to static testing and DOWN to driving characteristics

17 2 Pile Testing > 2.2 High Strain Dynamic Load Testing PDA Testing Restrike Tests allow time-dependence of capacity to be established, and trends in post-installation capacity increase (setup) or decrease (relaxation) to be taken into account for correlation with reference static test Driving Tests relate directly to driving criteria and therefore allow linkage with typical acceptance criteria (Energy- Capacity-Movement relationship) R = EMX s + 0.5C Pile SP38 Set = 0.9 mm/blow TC = 6 mm

18 Capacity [kn] 2 Pile Testing > 2.1 Static Load Testing > Time dependent capacity changes The importance of time dependency Multiple PDA tests can establish time dependency trends PDA restrike tests can be performed just before or after a static test (or both before and after) to better frame the comparison 2,500 2,000 1,500 1, capacity vs time PDA/CW capacity static capacity Time [days]

19 2 Pile Testing > 2.2 High Strain Dynamic Load Testing > Reliability of Dynamic Pile Tests PDA/Capwap a capacity INFERENCE Dynamic testing analysis by wave matching (e.g. Capwap) is based on simple static/dynamic soil models. Capacity is INFERRED. The quality of the match reflects the relevance of the models to 'truth' Measures Type A Type B Type C Occurrence >95% <5% 1% Match Quality Good Good Poor Capacity Range Narrow (< 10%) Wide (> 20%) Uncertain Recommendation Static test to ultimate capacity* Best Match or Upper Bound Lower Bound or Static Correlation Safe Lower Bound if it can be assured Optional Yes, unless LB used Yes * Static testing to ultimate capacity is always best practice as long as requirements and limitations are understood

20 Relative Probability 2 Pile Testing > 2.2 High Strain Dynamic Load Testing > Reliability of Dynamic Pile Tests The reliability of Wave Matching analysis % DLT : 1/ g = % DLT: 1/ g = % DLT: 1/ g = % DLT : 1/ g = If static testing provides an accurate and relevant reference then dynamic potentially overestimates by up to 30% This overestimate is 'covered' by a g of 0.75 [10% dynamic] 20% 18% 16% 14% 12% 10% 8% 6% 4% 2% 0% Chambers and Lehane (2011) : reduced 42 tests Likins and Rausche (2008) : 197 tests Ratio of dynamic: static (DLT / SLT)

21 Geotechnical Credibility and Oversight The following 2 cases highlight the importance of analyses being geotechnically informed They also highlight the importance of effective geotechnical review and oversight

22 Case 1 :Capwap vs Borelog near pile toe Depth below ground (m) Auto Shaft/Toe (kpa) Manual Shaft/Toe (kpa)

23 4 Summary Geotechnical credibility Case 2 Marine piling may require simultaneous assessment of tension, compression and embedment for lateral capacity for pile sign-off Time for assessment and sign-off is critical Fast turnarounds are often specified

24 5 Geotechnically credible solutions Automatic vs "Geotechnical " Analysis With Auto matching the testing rate was increased to 100% of piles After Manual matching the testing rate was reduced back to 15% of piles Auto Manual

25 5 Geotechnically credible solutions Automatic vs "Geotechnical " Analysis For marine piles (uplift) shaft resistance is often critical Auto Manual Total Capacity : kn kn Shaft : kn kn

26 4 Reliability through Solution Consistency Consistency of solution If a consistent set of dynamic and static soil parameters can be applied generally across a suite of tests, that modelling solution gains greater credibility through the universality of its application A master database allows consistency of tests to be reviewed in tables and graphs, e.g. physical parameters PDA parameters Capwap parameters

27 4 Summary Summary Paper 1 Static testing is the reference test for a single pile test but is hard to extrapolate On a project basis, static testing* can provide a reference or calibration for dynamic tests A primary benefit of dynamic tests is they are extensive The inferred capacity error * is generally less than 10% (A) and less than 25% (B), which is fully compensated by normal g values * if conducted properly

28 Paper #2 Enhanced Use of Dynamic Pile Testing in Foundation Engineering ANZ 2015 Wellington, NZ February, 2015 Dr. Julian Seidel

29 Dynamic Formulas the good, the bad and the ugly

30 2 Pile Testing > 2.2 High Strain Dynamic Load Testing PDA Testing Restrike Tests allow time-dependence of capacity to be established, and trends in post-installation capacity increase (setup) or decrease (relaxation) to be taken into account for correlation with reference static test Driving Tests relate directly to driving criteria and therefore allow linkage with typical acceptance criteria (Energy- Capacity-Movement relationship) R = EMX s + 0.5c Pile SP38 Set = 0.9 mm/blow TC = 6 mm

31 Dynamic Formulas comprehensively discredited Convention Very low reliability Use in sand and rock, not clay Ratios to capacity vary within and between sites Use as standalone for untested piles anyway Comment Most studies pre 1980 against static and before PDA Predict Driving Resistance Dynamic component of resistance varies between sites and with driving condition Use but use with understanding (and correlation) Inopiles International Pte Ltd

32 3 Pile Monitoring Pile Driving Monitor Safe (from 10m) and accurate (0.1mm) measurement of set, TC Measures position at 4000Hz So pile velocity can be computed Pile velocity is affected by hammer impact energy ( v E ) 3M disposable reflector attached to pile PDM 10m from pile

33 3 Pile Monitoring Variation in peak pile velocity The peak pile velocity reflects variations in hammer performance and hammer and pile cushion properties A variation in v peak of 1.59 to 1.92 m/s suggests a 45% variation in delivered energy R = EMX s + 0.5c

34 3 Pile Monitoring Variation in delivered energy concrete piles The same project showed a variation of -37% +27% about average for controlled drop height o min 42.0 kj o max 84.5 kj Acceptance criteria should adjust for energies to individual piles

35 2 Inference of capacity from input and response Inference of capacity Apply and Measure Input Dynamic Test : WaveDown Infer system property Measure Pile Response Dynamic Test : WaveUp Static Test : Load Capacity (C) Static Test : Deflection Untested : Stroke (E) ECM Relationship Untested : Movement (M)

36 3 The Nexus between Energy Capacity and Pile Movement Typical ECM Relationships Hiley Formula R = e x M x h s + 0.5(c 1 +c 2 +c 3 ) [M m + n 2 (M f + M p )] M m + M f + M p Wave Equation (WE) Bearing Graph R E 1 E 2 E 3 R E 1 E 2 E 3 1/set set

37 3 The Nexus between Energy Capacity and Pile Movement The golden reference for the pile system Static load testing is the 'golden reference' for the evaluation of a single pile capacity The Energy-Capacity-Movement relationship is the 'golden reference' for the determination of the capacity of untested piles for a given hammer-pile-foundation system Static testing is the reference for correlation of single dynamic tests The ECM relationship is the reference for development of a consistent suite of dynamic tests. The ECM guides the installation of all untested piles (usu. 90%+)

38 3 The Nexus between Energy Capacity and Pile Movement Internally inconsistent PDA tests These tests are for same hammer, energy and pile The tests may suggest that capacity is 9500kN regardless of set Or that a set of 1.5mm achieves capacities between 9.7 and 14.6MN

39 2 Pile Testing > 2.1 Static Load Testing > Low Statistical Representation Wave equation capacity-set relationships The tester provided WE bearing graphs matching each analyses At 8mm set, these curves suggest capacities between 3.8 and 9.8MN The tests don t provide clarity for acceptance of untested piles in the form of a consistent ECM relationship

40 4 Summary Pile capacity control - case study Marine piling is generally driven based on set or blow count alone Hence the bearing graphs just seen DRF = ECM Capacity / Reference Capacity

41 5 Geotechnically credible solutions Capacity-set trendline (Capwap vs set) There is a clear trend but there is significant scatter. Why?

42 5 Geotechnically credible solutions Driving formula/capwap trendline (DRF vs set) The trendline is developed from correlation of dynamic formula and Capwap The trend for the project is clear, with DRF increasing as set increases

43 6 Isolated Test Approach and Quick Turnaround Analysis The 1 hour Capwap analysis (Marine) Specifications sometimes require Capwap analysis in 1 hour This has unintended consequences. The 1 hour approach The ECM approach Fast automatic analysis (Slow) manual analysis No geotechnical input Geotechnically informed No review of consistency Consistent parameters, results Project confusion Clear project guidance Reliance on individual tests Sign-off on project-wide basis Sometimes (much) more testing Relatively less testing

44 Piling Targets and Real-time sign-off

45 8 Implementation of a System Approach Implementing an ECM System Approach Recognize that Capwap is not unique ( 5-10% generally and < 25%) First 5 or 6 Capwap analyses are considered draft Establish the ECM relationship based on the initial analyses (correlated dynamic formula, suite of bearing graphs etc.) Adjust and re-issue the 5 or 6 initial Capwap analyses with consistent parameters that support the ECM ALL piles (tested or untested) are accepted by the ECM and whatever other criteria are required for conformance (zero delay << 1hour!) Ongoing review of ECM relationship

46 8 Implementation of a System Approach The need for monitoring of every pile Measured Energy (kj) Effective Monitoring of energy and movement Energy variations even for hydraulic hammer on steel piles varies -16% to +20% about average All piles are as important as each other, whether tested or not Steel pile with modern hydraulic hammer Measured Energy EMX Sequence of dynamic tests

47 3 Pile Monitoring QA/Capacity estimation for untested piles Pile Driving Monitor (PDM) combined and correlated with PDA / Capwap for reliable energy capacity and movement estimation for all untested piles PDM in use offshore in Mauritius for both continuous driving records and final capacity assessment

48 4 Summary Summary Paper 2 PDA/Capwap should be mindful and geotechnically informed Automatic Capwap analysis does not meet either criterion Reviewers should do credibility checks on both individual Capwaps and on the suite of results Mindless analysis can misinform and lead to increased testing A system approach based on establishing the underlying ECM relationship is recommended Such an approach will provide an informed and consistent assessment, clear guidance, and faster sign-off.

49 Thank you Questions? AGS Perth, WA 12 May, 2015 Dr. Julian Seidel