CAPWAP rules Important!

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Christian Ashley Pierce
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2 inch (5 mm ) usually 0.1 inch; 2.5 mm SS, ST < 0.4 s/ft (1.3 s/m ) if higher, use SK model CS, CT 0.3 to 1.

1 CAPWAP rules Important! Unit friction < 4 ksf (200 kpa ) for most soils QT (+TG) < Dmax, toe to assure activation QS < 0.2 inch (5 mm ) usually 0.1 inch; 2.5 mm SS, ST < 0.4 s/ft (1.3 s/m ) if higher, use SK model CS, CT 0.3 to 1.0 CS < 3.0 if SK used Match set / blow (has penalty if set difference > 1 mm) use SK (radiation damping) for low set / blow, drilled piles do NOT use SK in high set / blow (< 3 BPI; > 8 mm / blow) low SK values may overpredict capacity

2 Record Selection - Quality 1. Use record of good quality Good proportionality No electronic or mechanical noise Integrates out to final set and zero velocity Force returns to zero Short rise time

3 Record Selection Energy Level a) For high resistance situation (set less than 3 mm/blow), find high energy/high force record b) For low resistance (set more than 10 mm/blow), find low energy/low force record c) Consider loss of setup or relaxation for restrike blow selection (more later on this)

$Acceleration zero line shift for correct final velocity and displacement (a small fraction of the maximum acceleration amplitude) 2.$

4 Data Adjustment 1. Acceleration zero line shift for correct final velocity and displacement (a small fraction of the maximum acceleration amplitude) 2. Calibration adjustment corrects for unknown pile properties, changing sensor constants, extreme cold temperatures (PR accelerometers)

Build Pile Model 1. Use 1 m pile segments or less 2. For records with very high frequency content or Rapid Impedance changes, use shorter pile segments - no point using less than.

5 Build Pile Model 1. Use 1 m pile segments or less 2. For records with very high frequency content or Rapid Impedance changes, use shorter pile segments - no point using less than.25 m segment length ( t =.05 to.06 ms) 3. Use 1m soil segments where shallow penetrations would yield less than 4 soil segments or when very good resolution is needed and warranted. 4. Use 2 m soil segments in most cases

slack input If no success, use reduced impedances 2.

6 Special Considerations: Pile Model for special cases 1. Uniform piles with Splices/Compression Slacks (show up within first 2L/c) Try matching with slack input If no success, use reduced impedances 2. Uniform piles with Tension Cracks (show up at and after 2L/c) Use tension slacks with low efficiencies (either force or deformation limited) Use Variable Time Increment (2014 version)

7 Pile Model for special cases - continued 3. For unknown Pile Shape (drilled shafts): Model uniform shaft Perform initial analysis Correct for reasonable resistance distribution Adjust impedances Later convert to area change in Pile Model (PM)

8 Pile Model for special cases - continued 3. For unknown Pile Shape (drilled shafts): Model uniform shaft Perform initial analysis Correct for reasonable resistance distribution Adjust impedances Later convert to area change in Pile Model (PM) 4. For unknown Wave Speed: Assume a wave speed, Attempt matching, adjust E of pile (correct force) Use overall wave speed change (no change of E) for piles with slight cracking

9 Toe quake sensitivity

10 Q t : (inch)

11 Shaft damping sensitivity

12 Js: (s/ft)

Check quake (particularly toe effect) (AQ) 2. Check damping effects (AQ) 3. Check unloading effects (AQ) 2.

13 Typical CAPWAP Procedure the easy part 1. Data input: select the proper record 1. Data adjustment (normally automatic) 2. Build pile model (normally automatic) 3. Interactively improve the soil model 1. Improve resistance distribution (AF) 1. Check quake (particularly toe effect) (AQ) 2. Check damping effects (AQ) 3. Check unloading effects (AQ) 2. Vary total capacity (RD or ARD) 3. Vary balance of shaft/toe resistance (also AT) 4. Repeat and find absolutely best match quality 2. Produce output

14 Summary of CAPWAP s Automatic Features AC AF AT AQ AQ AQ-Std Automatic CAPWAP (after user initialization) Calculate shaft resistance parameters Calculate a set of toe parameters Select and change multiple CW variables for BM Change current CW variable for BM Change CW standard variables* for BM ARD ARDQ Static/dynamic resistance exchange with user interaction Quick Static/dynamic resistance exchange AR ST Automatic balance of shaft/toe resistance (2014) *CAPWAP Standard variables: SS, ST, QS, QT, TG, UN, CS, CT

15 Find best MQ Adjust individual segment resistances to improve match automatic feature may smoothen distribution too much 1. Investigate shifting resistance between shaft to toe with appropriate quake and damping adjustments (AR ST) 2. Use ARD (or ARDQ) to vary capacity and check R U 3. Use AQ (Automatic Quantity improvement) on individual quantities or groups of CAPWAP variables 4. Do not spend excessive effort on late record portion unless it does affect the capacity/distribution results

16 Absolutely best MQ? Automatic searches may not be realistic, when The match has been achieved with an unreasonable set of parameters an engineer s review is required Data characteristics are unusual e.g. data quality an engineer s responsibility to check Pile model adjustments are required - e.g. slacks and/or Impedance variations engineer s decision Soil conditions modeling with radiation damping, residual stress analysis, shaft mass or plug effects, etc. - engineer s decision

17 Unusual Circumstances 1. Unusually High Damping Needed a) Maybe OK for low velocities (drilled shaft testing) b) May point to need for Radiation Damping Model

18 About Radiation Damping 1. Radiation Damping reasonable when a) Blow count very high (low set per blow) b) Open ended pipes/h-piles (plug effect) c) Match improves significantly with reasonable Smith damping factors 2. Radiation Damping unreasonable for a) Very cohesive or plastic soils b) Low blow counts P i l e S e g m e n t MS SK

19 Unusual Circumstances 1. Unusually High Damping Needed a) Maybe OK for low velocities (drilled shaft testing) b) May point to need for Radiation Damping Model 2. Wave return stretched out unlike impact signal a) Likely due to tension cracks needs tension slacks, reduced overall wave speed or variable time increment (CW 2014) 3. Splices with Compressive Slacks (e.g. follower on concrete pile) a) Use compressive slack and impedance reduction 4. Unusual Resistance Distribution a) Maybe needs Residual Stress Analysis b) Data Quality?

20 Final considerations You tried everything Resistance distribution reasonable Agreement with other methods reasonable Match Quality less than 5 If all above, quit and do output

21 CAPWAP Static Analysis Options Smoothing User Capacity Uplift Test Extrapolation Displacement (in) Load(kips) PileTop Bottom PileTop* Bottom* Ru =1105.4kips Rs = 780.0kips Rb = 325.4kips Dy = 0.79in Dx = 1.41in *Extrap Note: CAPWAP performs a t-z/q-z analysis with an elasto-plastic soil model.

22 CAPWAP Limitations Incomplete Resistance Activation small set per blow < 1/10 inch; 2.5 mm What to do? Bigger hammer; higher energy hammer Caution Watch stresses! No point exceeding 6 to 8 mm set per blow ( 1/4 to 1/3 inch per blow )

23 Underprediction Temporary Loss of Capacity during driving Increased pore water pressure? Arching? Other? What to do? 1. Restrike after sufficiently long wait 2. Use early, high energy blow! 3. Use Radiation Damping model ( if low set/blow, if drilled shaft) 4. Use superposition of EOD and BOR (only if BOR set per blow small < 2 mm)

24 Underprediction Loss of Setup Increasing Energy Analyze several blows Superposition resistance envelope ( only if refusal blow count ) 610 mm PSC, Pier A Load (kn) Top Toe Displacement (mm)

25 Does CAPWAP have a Unique Solution?

26 Many ways to apply load in a static test Also, Maintained, Quick, CRP loading

27 Static Load Test does not give a unique result! All get similar answers Get many different answers from different interpretations of failure

28 Failure criteria no unique answer Load (tons) 250 Chin 1.30 Brinch-Hansen 80% 1.17 Mazurkiewicz 1.15 Van Der Veen 1.13 Fuller and Hoy 1.12 De Beer 1.03 Butler and Hoy 1.02 Davisson 1.00 D/ D/30 + elastic D/ After Fellenius, Guidelines for the Movement Interpretation (inch) of static loading tests

4% Chin-Kondner Brinch Hansen 80% Davisson Not Unique!

29 Tangent Butler-Hoy Corps of Engr. Brinch Hansen 90% Fuller-Hoy Mazurkiewicz Housel DeBeer Shen-Nu Static Load Test Evaluations Range 0.73 (DeBeer) to 1.42 (Chin) COV 18.4% Chin-Kondner Brinch Hansen 80% Davisson Not Unique! Q/Qavg Duzceer & Saglamar, Evaluation of Pile Load Test Results DFI Conference - Nice France, 2002

30 To obtain good correlation of PDA with static testing must activate all resistance in dynamic test (minimum 2 to 3 mm set per blow) allow strength changes to occur (restrike test) (set-up increase on shaft, relaxation at toe) consider 3 dates: install, static and dynamic tests must have high quality static test (good measurements, test to failure) if either test not to failure, gives lower bound solution only

31 24-inch PSC+H Silty and Calcareous Sand

32 CAPWAP (CW) versus Static Load Test (SLT) 25.0% 20.0% Distribution of CW / SLT Ratios (96&SW: N=226) CW versus SLT combined (N=303) (80, 96, SW) Frequency 15.0% 10.0% 40,000 Unconservative (potentially unsafe) 5.0% 0.0% under over ,000 Ratio CW [kn] 20, % 20.0% Distribution of CW / SLTmax Ratios (96&SW: N=179) 10,000 0 Frequency Conservative (residual strength) 0 10,000 20,000 30,000 40, % 10.0% 5.0% 0.0% under Ratio over 130 SLT [kn]

33 Question 1: is CAPWAP result unique? Question 2: is any variation significant? Answer: results of experienced testers have little variation Discuss in more detail

34 Pipe in Silt H-pile in Sand COV 5% COV 6% Long pipe, very sensitive clay Pipe, weak crushing sandstone COV 13% COV 14% Variation of CAPWAP Results as a Function of the Operator by Fellenius, Third Int l Conf. on Application of Stress-wave Theory to Piles, 1988

35 CAPWAP - Results SLT +20% -20% CAPWAP Case Method CAPWAP

CAPWAP - Results SLT +20% -20% Unique solution? Case Yes - if you CAPWAP pursue to get the absolute minimum Method CAPWAP error in Match Quality. 14 3 But does it really matter?

36 CAPWAP - Results SLT +20% -20% Unique solution? Case Yes - if you CAPWAP pursue to get the absolute minimum Method CAPWAP error in Match Quality But does it really matter? No since solutions are generally all similar (within reasonable tolerance) and different blows may give slightly different answers Static test interpretation also is not unique!

37 CAPWAP might be more unique than Static Load Test interpretation! All get similar answers Get many different answers from different interpretations of failure

38 Dynamic Load Test result (CAPWAP) is generally conservative CAPWAP on average less than Davisson Davisson generally rather conservative Continued set-up on most piles after the DLT Group effects densification during production Most piles driven harder than criteria DLT often used with slightly higher S.F. Better site coverage by more DLT Possibly less risk with DLT than with SLT

39 CAPWAP Is a signal matching software Is absolutely essential for evaluation Is state-of-the-practice ( gold standard ) Interactive with user guided auto searches Is the ultimate answer for DLT capacity Guides selection of JC for Case Method Evaluates stresses vs. depth Models non-uniform piles, et.al.

40 Parting Comments and Advice. Many codes require signal matching (e.g. AASHTO) CAPWAP is only signal matching software that has been compared with an extensive correlation database Failure to use CAPWAP is contrary to state-of-practice Do whatever it takes to become proficient and thereby obtain the best possible results and reduce legal exposure Seek second opinions for difficult cases

41 Thanks for your attention HAPPY CAPWAP-ING

Additional Pile Design Considerations

Additional Pile Design Considerations PDCA 2015 Professor Driven Pile Institute Patrick Hannigan GRL Engineers, Inc. What Are Additional Pile Design Considerations? Time Dependent Soil Strength Changes