CAPWAP
®
Introduction
PDCA Professor’s Institute
June 2011
Garland Likins
Pile Dynamics, Inc.
“CAPWAP” is a registered trademark of Pile Dynamics, Inc.
CAPWAP
is a
“Signal Matching” Program
I
(System Identification; Reverse Analysis)
We know both Input and Response
(wave down and wave up)
But we do not know the “System”
( static and dynamic soil model )
R
“System” includes Pile and Soil
Driven Pile properties are known.
Soil parameters must be determined.
Input into CAPWAP program includes:
• Measured force and velocity versus time
• Pile properties (known for driven piles)
• Penetration (embedment depth)
• Set per blow (or “Blow count”)
• difficult to assess super-accurately
WDM
THE CAPWAP METHOD
WUM
WUC
1 Set up pile and soil model and
assume Rshaft and Rtoe
2 Apply measured WDM to pile model at top
and calculate complementary WUC
Rshaft
3 Compare WUC with measured WUM
4 Adjust Rshaft and Rtoe
5 If not satisfactory
match: Go to Step 2
Rtoe
Repeat until match
is satisfactory
The Pile Model
Li
Zi-1
Zi


t =Li/ci

Zi+1
The Pile is divided in Np
uniform pile segments
of approx. 1 m length.
Each segment has
impedance Zi = EiAi/ci
and wave speed ci
The Wave travel time,
t, is the same in all
segments (.2 to .25 ms)
The CAPWAP Soil Model
t
t
t
Pile segment length ~ 1 m
Soil segment length ~2 m
( resolution of the data itself )
t
t
t
t
Spring (static resistance)
Dashpot (dynamic resist)
RNs-1
The
CAPWAP
Soil
Resistance
Model
Rui, qi
Ji
RNs
Shaft Resistance,
Ns times
tG
Rt, qt
mPL
JT
Some
CAPWAP
Soil Model
Extensions
Ji
Rui, qi
ms
mSP
JSK
tG
Rt, qt
JT
mt
JBT
Add: Radiation Damping
Mass ms related to circumference
Damper Jsk related to soil strength
Add: Shaft soil plug
Static Shaft Resistance Model
Rs
Ru,s
Rs
d
Rs
quake, qs
unloading quake,
qs cs
Ru,n : UN = -Ru,n/Ru,s
CAPWAP Static Toe Resistance Model
Rt
Ru,toe
Rt
quake, qt
Toe gap: tg
d
unloading
quake, qt ct
Pile
CAPWAP Damping Model
Viscous (Option=0)
Rd = JC Z v = RU JS v
velocity
v
Js = Jc Z/RU
Smith (Option=1)
Rd = RS(t) JS v
Combined (Option=2)
Rd = RS JS v until RS = RU
Rd = RU JS v after RU is achieved
Smith (Option: OP1 or OP2)
Often with large toe quake
Normal CAPWAP Unknowns
Main Parameters
Rui:
NS values at shaft +1 value at toe
Ji:
1 value at shaft +1 value at toe
qi:
Loading - 1 value at shaft +1 value at toe
Major Trimming Parameters
1 shaft + 1 toe unloading quake multiplier
1 shaft unloading level + 1 toe plug + 1 toe gap
1 toe damping option + 2 rad. damping values
Total NS + 9 (or 11) unknowns
For 20 m (66 ft) penetration: 19 or 21 unknowns
Match Quality Time periods
Period I: 2L/c
Shaft Res.
Distr. develops
III: tr+5ms
II:
tr+3ms
IV: 25 ms
Toe Res. and total
Capacity develops
tr
Unloading develops
An Example CAPWAP
First Trial Analysis (Lousy Match)
Input v
Matching F
or
Input F
Matching v
or
Input F
Matching F
( Best: apply inputs, calculate reflections )
Working with Wave-Up
RU = 782 kips
RT = 68 kips
JS/JT = .05/.15 s/ft
(JCS/JCT = .75/.22)
QS/QT = .10/.12”
RU = 782 kips
RT = 400 kips
(raise toe bearing)
RU/RT = 765/686 kips
JS/JT = .26/.07 s/ft
(JCS/JCT = .44/.97)
QS/QT = .06/.12”
Unloading Parameters
Pretty good match: let’s quit
Plotted Output
EX2;
CLARK; SOFT-ROCK;
Pile: EX-2
GRL Engineers,
Inc.
MKT DE 70B, HP 14 X 89; Blow: 627
GRL Engineers, Inc.
Test: 02-Jun-1993
OP: FR
CAPWAP® 2003-1
CAPWAP FINAL RESULTS
CAPWAP FINAL RESULTS
Total CAPWAP
CAPWAP Capacity:
Capacity:
Total
Soil
Sgmnt
No.
Dist.
Below
Gages
ft
ft
1
2
1
3
2
4
3
5
6
4
7
5
8
6
9
7
10
11
8
12
9
13
6.7
13.5
79.4
20.2
86.0
26.9
92.6
33.7
40.4
99.2
47.1
105.8
53.8
112.5
60.6
119.1
67.3
74.0
125.7
80.8
132.3
87.5
804.4; along
along Shaft
Shaft
764.6;
Depth
Below
Grade
ft
ft
4.2
11.0
5.8
17.7
12.4
24.4
19.0
31.2
37.9
25.7
44.6
32.3
51.3
38.9
58.1
45.5
64.8
71.5
52.1
78.3
58.7
85.0
Ru
Force
in Pile
kips
kips
kips
Sum
of
Ru
kips
kips
2.0
1.0
16.9
1.0
9.5
1.0
1.9
2.0
3.0
0.0
4.0
0.0
18.6
0.0
1.0
6.5
1.0
1.0
11.3
4.9
11.3
39.1
764.6
762.6
804.4
761.6
787.5
760.6
778.0
759.6
776.1
757.6
754.6
776.1
750.6
776.1
732.0
776.1
731.0
769.6
730.0
729.0
758.3
724.1
747.0
685.1
2.0
3.0
16.9
4.0
26.4
5.0
28.3
7.0
10.0
28.3
14.0
28.3
32.6
28.3
33.6
34.8
34.6
35.6
46.1
40.5
57.4
79.5
kips
10
138.9
65.3
6.5
11
145.5
72.0
6.5
Avg. Skin
6.1
12
152.2
78.6
6.5
Toe
685.1
13
158.8
85.2
6.5
14
165.4
91.8
6.5
Soil Model Parameters/Extensions
15
172.0
98.4
6.5
Case Damping Factor
Unloading
Quake
Avg. Skin
Reloading Level
Unloading Level
Toe
740.5
734.0
727.5
721.0
714.5
708.0
(% of 6.4
loading quake)
(% of Ru)
(% of Ru)
708.0
Soil Model Parameters/Extensions
CAPWAP
match quality:
Case Damping
Factor
Observed:
Reloading final
Level set =
Observed: final set =
Unloading Level
96.4;
79.5; at
at Toe
Toe
2.88 (Wave Up Match)
0.050
(% ofin;
Ru)blow count =
0.009 in; blow count =
(% of Ru)
63.9
70.4
76.9
83.4
89.9
96.4
708.0
685.1 kips
kips
Unit
Unit
Resist. Resist.
(Depth) (Area)
kips/ft
ksf
kips/ft
ksf
0.30
0.15
2.55
0.15
1.44
0.15
0.29
0.30
0.45
0.00
0.59
0.00
2.76
0.00
0.15
0.98
0.15
0.15
1.71
0.73
1.71
5.80
0.06
0.03
0.27
0.03
0.15
0.03
0.03
0.06
0.10
0.00
0.13
0.00
0.59
0.00
0.03
0.10
0.03
0.03
0.18
0.16
0.18
1.24
Smith
Damping
Factor
s/ft
s/ft
Quake
0.255
0.255
0.243
0.255
0.243
0.255
0.243
0.255
0.255
0.000
0.255
0.000
0.255
0.000
0.255
0.243
0.255
0.255
0.243
0.255
0.243
0.255
0.060
0.060
0.100
0.060
0.100
0.060
0.100
0.060
0.060
0.100
0.060
0.100
0.060
0.100
0.060
0.100
0.060
0.060
0.100
0.060
0.100
0.060
in
in
0.98
0.98
0.94
0.98
0.98
0.98
Skin
0.98
0.10
0.10
0.19
0.10
503.31
0.10
0.10
Toe
0.10
0.437
99
0.98
100
78
0.971
100
0.10
100
0.243
0.100
100.16
0.092
0.830
Skin
Toe
0.111
0.309
100
240 b/ft
100
1323 b/ft
75
0.243
0.243
0.255
0.243
0.066
0.243
0.243
0.243
Table
Output
0.100
0.100
0.060
0.100
0.120
0.100
0.100
0.100
Smith Type
Ji, qi,
Ri
EXTREMA TABLE
Table
Output
Pile
Sgmnt
No.
1
2
4
6
8
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
Extrema
Absolute
Dist.
Below
Gages
max.
Force
min.
Force
max.
Comp.
Stress
max.
Tens.
Stress
max.
Trnsfd.
Energy
max.
Veloc.
max.
Displ.
ft
kips
kips
ksi
ksi
kip-ft
ft/s
in
3.4
6.7
13.5
20.2
26.9
33.7
37.0
40.4
43.8
47.1
50.5
53.8
57.2
60.6
63.9
67.3
70.7
74.0
77.4
80.8
84.1
87.5
586.4
588.7
585.7
587.3
590.1
594.8
592.6
598.9
596.6
607.0
602.3
608.4
568.4
576.1
589.0
624.9
668.4
718.3
756.7
785.1
793.0
806.4
-24.4
-24.1
-22.1
-21.1
-19.6
-18.4
-17.0
-17.2
-15.3
-16.4
-15.2
-15.4
-7.2
-17.7
-27.0
-35.8
-42.0
-48.2
-54.5
-61.7
-61.2
-63.8
22.549
22.635
22.520
22.583
22.691
22.870
22.787
23.029
22.940
23.339
23.161
23.393
21.857
22.152
22.650
24.028
25.701
27.622
29.095
30.188
30.492
31.007
-0.937
-0.927
-0.849
-0.810
-0.753
-0.706
-0.653
-0.661
-0.590
-0.629
-0.585
-0.592
-0.276
-0.682
-1.039
-1.376
-1.613
-1.852
-2.095
-2.371
-2.355
-2.451
23.53
23.40
22.79
22.30
21.73
21.02
20.42
20.09
19.39
19.05
18.21
17.79
15.45
14.91
14.16
13.38
12.39
11.36
10.14
8.94
7.59
6.21
11.7
11.6
11.5
11.4
11.2
11.0
10.9
10.8
10.6
10.4
10.2
10.0
9.9
9.8
9.7
9.6
9.4
9.2
8.8
8.1
6.8
5.3
0.738
0.725
0.699
0.670
0.637
0.600
0.579
0.559
0.539
0.518
0.496
0.473
0.449
0.423
0.394
0.363
0.329
0.293
0.255
0.216
0.178
0.140
87.5
87.5
31.007
(T =
(T =
-2.451
27.2 ms)
44.2 ms)
CASE METHOD
Case Method
J = =
RS1
RMX
RSU
0.0
830.3
862.6
836.4
RAU=
595.0 (kips);
Current CAPWAP Ru=
0.1
799.1
839.8
805.8
RA2=
0.2
767.8
821.8
775.2
0.3
736.6
808.3
744.6
0.4
705.3
795.0
713.9
0.5
674.1
782.0
683.3
0.6
642.9
769.8
652.7
0.7
611.6
757.8
622.1
0.8
580.4
745.7
591.4
757.7 (kips)
764.6 (kips);
Corresponding J(Rs)=
0.21; J(Rx)=0.64
0.9
549.2
733.7
560.8
Recommended CAPWAP Procedure
1. Data input: select the proper record
1. Data adjustment (normally automatic)
2. Build pile model (normally automatic)
1. Improve resistance distribution
1. Check quake (particularly toe effect)
2. Check damping effects
3. Check unloading effects
2. Repeat
3. Repeat to find “absolutely” best match quality
2. Produce output
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 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
• Match set / blow
CS < 3.0 if SK used
(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 ( > 8 mm / blow; < 3 BPI )
• low SK values may overpredict capacity
Record Selection
We cannot completely control the test!
1. For high resistance (set < 3 mm/blow; > 8 BPI)
find high energy/high force record
2. For low resistance (set > 8 mm/blow; < 3 BPI),
find blow with low energy/low force
or reduce energy input to pile
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 )
Underprediction
Loss of Soil Resistance during driving
•
•
•
Increased pore water pressure?
Soil fatigue or Strain loosening?
Liquefaction?
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 set per blow very small - < 2 mm)
Underprediction
Loss of Setup – Increasing Energy
Incomplete Activation
Reduced Capacity
Energy
Capacity
Blow Number
Underprediction
Underprediction
Loss of Setup – Increasing Energy
• Analyze several blows
• Superposition resistance envelope
(if refusal blow count)
610 mm PSC, Pier A
6000
5000
Load (kN)
4000
Top
Toe
3000
2000
1000
0
0
10
20
30
Displacement (mm)
40
50
Overprediction ?
1. Relaxation
1.
2.
3.
4.
Weathered Shales
Negative Porewater Pressure (saturated silts)
Heave
Solution: restrike after wait time.
2. Excessive Energies (causes set > 8 mm / blow )
Just harder to get a match
Solution: use less energy to reduce set / blow
Correlation requires
a static load test
Continued correlations
assure reliability.
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


1000 days
100 days
10 days
1 day
capacity
Test Comparisons - cohesive soils
2nd PDA test
@ 15 days
Static test @ 14 days
PDA Test @ 12 hours
log time
24-inch PSC+H
Silty and Calcareous Sand
(after Duzceer & Saglamar, DFI Nice 2002)
Evaluation of
24 static tests.
conservative
Different
interpretation
methods give
different answers.
Davisson method
for driven piles is
conservative.
Individual method
result (AVG of 24
tests) compared
to AVERAGE of all
method results.
aggressive
Interpretation Method
DeBeer
Housel
Corps of Engineers
Davisson
Tangent Intersection
Shen-Niu
Butler-Hoy
Brinch-Hansen 90%
Fuller-Hoy
Mazurkiewicz
Brinch-Hansen 80%
Chin-Kondner
Avg.
COV
0.768
0.822
0.913
0.945
0.998
1.008
1.025
1.075
1.091
1.153
1.240
1.511
0.210
0.120
0.095
0.092
0.086
0.086
0.081
0.044
0.067
0.072
0.176
0.326
Study
1980
1996
1996
SW
All
Avg.
1.010
0.931
1.012
0.993
0.980
COV
Co
N rrel notes
0.168
0.9
77 60 Case (CWRU) original study
0.166
0.9
83 27 best match (B.M.)
0.097
0.9
83 67 radiation damping
0.165
0.9
143 84 all piles
0.169
0.9
303 83 (1996 – uses B.M. data)
Likins, G. E., Rausche, F., August, 2004. Correlation of CAPWAP with Static Load
Tests. Proceedings of the Seventh International Conference on the Application of
Stresswave Theory to Piles 2004: Petaling Jaya, Selangor, Malaysia; pg.153-165.
Distribution of CW / SLT Ratios (96&SW: N=226)
25.0%
20.0%
40,000
Frequency
CW versus SLT combined (N=303) (80, 96, SW)
Unconservative
(potentially unsafe)
15.0%
10.0%
5.0%
un
de
r7
0
70
-7
4
75
-7
9
80
-8
4
85
-8
9
90
-9
4
95
-1
00
10
110
10 5
611
0
11
111
11 5
612
12 0
112
5
12
613
ov 0
er
13
0
0.0%
30,000
Distribution of CW / SLTmax Ratios (96&SW: N=179)
20,000
25.0%
20.0%
Frequency
10,000
15.0%
Conservative
(residual strength)
10.0%
5.0%
0.0%
0
0
10,000
20,000
30,000
40,000
un
de
r7
0
70
-7
4
75
-7
9
80
-8
4
85
-8
9
90
-9
4
95
-1
00
10
110
5
10
611
11 0
111
11 5
612
0
12
112
12 5
613
ov 0
er
13
0
CW [kN]
Ratio
Ratio
SLT [kN]
CAPWAP (CW) versus Static Load Test (SLT)
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
®
iCAP
• iCAP is a quick signal matching program
• The quickness of iCAP compared to CAPWAP
makes a signal matching result available even
during the installation of the pile.
• For uniform driven piles under simple pile/soil
interaction conditions, iCAP will give
•
•
•
•
Total pile capacity
Distribution of shaft resistance and end bearing
Case Method damping factor for best correlation
Tension and compression stresses along pile shaft
• The results are independent of users
if no CAPWAP adjustments are performed
Use iCAP® on PAX
iCAP® on PDA-W
iCAP® and CAPWAP
• iCAP will not fully replace CAPWAP
• Very unusual soils (e.g. high match quality)
• Piles with cracks, gaps, slacks, shaft plugs
(open sections)
• iCAP uses CAPWAP models, but only searches
standard soil parameters automatically
• It is possible to perform iCAP on each pile, and
even each record
iCAP® performance
（7/20/2010）
iCAP example
Quick iCAP
Ru 493 kips
CSC 3.15 ksi
TSC 0.22 ksi
MQ 2.12
CAPWAP
506 kips
3.17 ksi
0.17 ksi
MQ1.48
CAPWAP Summary
Signal matching primarily involves changing static
resistance distribution and damping quantities to
get best fit response and obtain static capacity
CAPWAP (on restrike) yields the most reliable
capacity results among all dynamic methods
( best to use BOR with sufficient wait time )
Select appropriate blow for analysis to assure
activation of resistance ( > 2 mm set / blow)
Superimpose results in extreme cases, either by
multiple blows, or by EOD plus BOR (if at refusal)
Engineer should carefully review result and combine
with other soil knowledge to get final answers