1. OMAE 2009 Honolulu, HI - May 31 to June 5 2009
CAPWAP AND REFINED WAVE EQUATION ANALYSES FOR DRIVEABILITY PREDICTIONS AND CAPACITY ASSESSMENT OF OFFSHORE PILE INSTALLATIONS
Frank Rausche, Matt Nagy, Scott Webster GRL Engineers, Inc. Liqun Liang Pile Dynamics, Inc.

2. Outline Background Problem Statement Procedures and Examples for
PDA Testing and CAPWAP
Bearing Graph and Driveability
Variable Soil Setup and Plugging Effects
Problem Statement
Procedures and Examples for
Blow Count Depth Matching (BCDM)
Refined Wave Equation Analysis (REWE)
Summary
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

3. Dynamic pile testing and analysis
Using Pile Driving Analyzer® measure pile top velocity during pile installation; monitoring results include
Stresses
Integrity
Hammer performance
Capacity estimate
Perform signal matching with CAPWAP® to calculate capacity plus resistance distribution
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

4. CAPWAP (Signal Matching) Result
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

5. Wave equation analysis
Based on Smith’s concept
Input requirement
Hammer properties
Driving system details
Pile geometry
Soil information
GRLWEAP analysis options include
Bearing Graph
Driveability
GRLWEAP Bearing Graph
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

6. Wave equation analysis
GRLWEAP Driveability Output:
Assumption: soil setup gain on shaft is function of log (time)
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

7. Problem Statement
We may do PDA/CAPWAP for one pile but need capacity assessment for others
 Do Refined wave equation analysis (REWE)
We may have a driving record but no measurements and have to assess bearing capacity
 Do Blow Count-Depth Matching (BCDM)
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

8. The REWE Procedure
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

9. REWE Example – Pile Details
1067 mm dia. OE pipe – 100 m long
3 pile sections
Wall thickness: 34 – 44 mm
Final penetration: 42 m
Final blow count: 17 bl / 0.25 m
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

10. REWE Example – Soil Details
Alternate layers of
Carbonate clays; Shear strength 100 to 450 kPa
Silty, calcareous sands; med. dense to dense
Soils increasing in strength with depth
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

11. REWE Example - Hammer Menck MHU 500T 294 kN ram weight
550 kJ maximum rated energy (1.87 m equiv. stroke)
500 kJ max. applied energy (1.70 m equiv. stroke)
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

12. Measurements
PDA Measurements 3.5 m below top of pile with 2 strain transducers and 2 PR accelerometers
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

13. REWE Example PDA - EOD Results
Transferred Energy (kJ)
473
Max. Top Stress (MPa)
224
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

14. REWE Example – EOD CAPWAP Results
Capacity Total/Toe (MN)
10.1/2.0
Damping Shaft/Toe (s/m)
0.5/1.3
Quake Shaft/ Toe (mm)
2.0/15
Blows/0.25 m 17
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

15. CAPWAP Analysis Force and Velocity Measurements plus pile impedance
Calculated Load-Set Curve
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

16. Wave Equation Model GRLWEAP Hammer Model
Driving System as per contractor
Pile Model with stabbing guides
Soil model from CAPWAP
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

17. CAPWAP and GRLWEAP Input/Output Values
Quantity
Default/
Measured/
Computed
GRLWEAP
First Trial
Damping Shaft/Toe (s/m)
0.5/1.3
Hammer Efficiency
0.95
Dr. System Stiffness (kN/mm)
N/A
Dr. System CoR
Pile Top Stress (MPa)
224
243
Transferred Energy (kJ)
473
429
Blow Count (Blows/0.25 m) 17 23
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

18. CAPWAP and GRLWEAP Input/Output Values
Quantity
Default/
Measured/
Computed
GRLWEAP
First Trial
Final
Damping Shaft/Toe (s/m)
0.5/1.3
0.4/1.0
Hammer Efficiency
0.95
1.0
Dr. System Stiffness (kN/mm)
N/A
8,000
Dr. System CoR
0.93
Pile Top Stress (MPa)
224
243
225
Transferred Energy (kJ)
473
429
Blow Count (Blows/0.25 m) 17 23
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

19. Comparison of measured with GRLWEAP calculated force and velocity
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

20. Second Procedure: BCDM
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

21. BCDM – Example properties as before
1st Step: Obtain driving log
Blow count vs depth
Hammers and Energy settings
Driving interruption durations
Maybe average of several pile driving logs
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

22. BCDM Get fs vs depth from geotechnical report (starting value)
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

23. BCDM Get qt vs depth from geotechnical report (starting value)
Determine from driving log match
Modified fs
Setup factor
Modified qt
Effective toe area
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

24. BCDM – Blow Count match Predict long term capacity from modified fs,
modified qt,
setup factor
effective toe area
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

25. Summary
The bearing capacity of offshore piles can be assessed by the following methods:
From measurements at EOD and CAPWAP capacity at EOD  Capacity at EOD
From monitored restrikes plus CAPWAP capacity including partial setup  Capacity at BOR – may be extrapolated to later times
For similar non-monitored piles using REWE
From driving record by BCDM  Extrapolated, estimated capacity from driving interruption information
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

26. Summary (continued)
REWE, the REfined Wave Equation analysis requires measurements and helps determine capacity for non-monitored piles driven in similar soils.
REWE requires matching of
Transferred energy and top stress from PDA
Blow count and CAPWAP capacity
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

27. Summary (continued)
BCDM, the blow count-depth matching procedure determines bearing capacity from driving behavior
Generally applied to the complete driving log, including energy and driving interruptions
Driving interruption or restrike information allows for soil setup assessment
Without measurements results depend on hammer performance assumptions
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..

28. Thank You, OMAE Conference
Rausche, Nagy, Webster, Liang
CAPWAP AND REFINED WAVE EQUATION ANALYSES FOR DRIVEABILITY PREDICTIONS AND CAPACITY ASSESSMENT OF OFFSHORE PILE INSTALLATIONS