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
Liqun Liang
GRL Engineers, Inc.
Pile Dynamics, Inc.
Outline
 Background
 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 …..
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 …..
CAPWAP (Signal Matching) Result
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..
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 …..
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 …..
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 …..
The REWE Procedure
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..
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 …..
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 …..
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 …..
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 …..
REWE Example
PDA - EOD Results
Transferred Energy (kJ)
473
Max. Top Stress (MPa)
224
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..
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 …..
CAPWAP Analysis
30000.0
kN
Force Msd
Velocity Msd
15000.0
D is p la c e m e n t (m m )
Load (kN)
0
2000
4000
6000
8000
20.00
10
100
0.0
4
-15000.0
Pile
L/c
ms
Pile Top
Bottom
10000 12000
0.00
40.00
Ru =
Rs =
Rb =
Dy =
Dx =
10137.5
8137.1
2000.4
52.4
67.1
kN
kN
kN
mm
mm
60.00
80.00
 Force and Velocity
Measurements plus
pile impedance
100.00
 Calculated Load-Set Curve
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..
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 …..
CAPWAP and GRLWEAP Input/Output Values
Default/
Measured/
Computed
GRLWEAP
First Trial
0.5/1.3
0.5/1.3
Hammer Efficiency
0.95
0.95
Dr. System Stiffness (kN/mm)
N/A
N/A
Dr. System CoR
N/A
N/A
Pile Top Stress (MPa)
224
243
Transferred Energy (kJ)
473
429
17
23
Quantity
Damping Shaft/Toe (s/m)
Blow Count (Blows/0.25 m)
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..
CAPWAP and GRLWEAP Input/Output Values
Default/
Measured/
Computed
GRLWEAP
First Trial
GRLWEAP
Final
0.5/1.3
0.5/1.3
0.4/1.0
Hammer Efficiency
0.95
0.95
1.0
Dr. System Stiffness (kN/mm)
N/A
N/A
8,000
Dr. System CoR
N/A
N/A
0.93
Pile Top Stress (MPa)
224
243
225
Transferred Energy (kJ)
473
429
473
17
23
17
Quantity
Damping Shaft/Toe (s/m)
Blow Count (Blows/0.25 m)
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..
Comparison of measured with
GRLWEAP calculated force and
velocity
30000.0
kN
Force Msd
Velocity Msd
15000.0
10
100
ms
0.0
4
-15000.0
L/c
Pile
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..
Second Procedure: BCDM
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..
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 …..
BCDM
Get fs vs depth from
geotechnical report
(starting value)
Rausche Nagy Webster Liang: CAPWAP and Refined Wave Equation Analyses …..
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 …..
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 …..
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 …..
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 …..
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 …..
Thank You, OMAE Conference
Rausche, Nagy, Webster, Liang
CAPWAP AND REFINED WAVE EQUATION ANALYSES FOR DRIVEABILITY PREDICTIONS AND
CAPACITY ASSESSMENT OF OFFSHORE PILE INSTALLATIONS