Pile Driving Analyzer® (PDA)
and CAPWAP®
Proven Pile Testing Technology:
Principles and Recent Advances
Frank Rausche, Ph.D., P.E.
2013 Louisiana Transportation Conference
●
Pile Dynamics, Inc.
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Outline
• Introduction
– The PDA History
– Basics of PDA testing
– Recent developments
•
•
•
•
•
•
Wave Equation Analysis
Stresses, damage prevention and detection
Bearing capacity from CAPWAP and iCAP®
Vibratory testing and analysis
Dynamic pile testing and the LRFD approach
Summary
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Pile Dynamics, Inc. - founded in 1972
Our Objective: to provide the necessary methods,
hardware and software for reliable quality assurance of
deep foundations
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The Pile Driving Analyzer®
a long history of improvements
1965
1997
1958
1982
1992
1973
2007
Conforms to
ASTM D 4945
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What is required?
Accurate, Reliable and Efficient Pile Top Force and
Velocity Measurements
Reusable lightweight
strain and acceleration
transducers for testing
any pile type
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Transducers Requirements
•
•
•
•
•
•
Accurately calibrated
Rugged and Reliable
Allow for self checking
Adapt to any pile type
Cost efficient
Allowing for testing
“after-the-fact” - when or if
needed
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Transducer Placement
2D
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Traditionally:
2 strain sensors +
2 accelerometers.
But frequently we
must use 4 strain
sensors for accuracy!
(large piles, spiral
welded, all drilled
shafts/piles, …)
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Smart, wireless Sensors
calibration transmitted with signal
 Sensors 
Transmitter
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Sensor-Transmitter Protection
• H-piles – no issue
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Sensor-Transmitter Protection
• H-piles – no issue
• Pipe piles – use protectors
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Lofting pile into leads
PDA
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Sensor-Transmitter Protection
• H-piles – no issue
• Pipe piles – use protectors
• Concrete piles – protectors
or - sensors in indentations
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Sensor-Transmitter Protection by
Indentation
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®
SiteLink Remote
PDA
USA Patent #6,301,551
Pile Driving Analyzer
Site A
Site B
Pile
Pile
Engineer
- controls several PDAs
simultaneously as if on-site
- monitors piles in real time
- reports within short time
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Contractor
- schedules easily
- keeps project going
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Design and Construction of Driven
Piles*
•
•
•
•
•
•
•
•
Soil Borings
Static pile analysis
Pile Type and Length selection
Wave Equation analysis to check driveability
Initial Pile Testing program by PDA
Develop driving criterion
Production pile installation to criterion
Dynamic testing of production piles as needed
*See Hannigan et al., 2006. Manual on the Design and Construction of Driven Piles; FHWA
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Wave Equation Analysis (GRLWEAP)
Thermodynamic model
predicts stroke for diesels
Enter
soil profile
Predicts Driveability
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Wave Equation Analysis (GRLWEAP)
Updated hammer/driving
system input
Updated soil parameters
Refined capacity vs. blow count after testing
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Dynamic Pile Testing Objectives
• Finding optimal installation procedure with
Dynamic Monitoring by Case Method for:
•
•
•
•
Hammer Performance
Driving Stresses
Pile Integrity
Soil Resistance at the time of testing
• Dynamic Load Testing:
• Capacity vs. time EoD/BoR – setup/relaxation
• CAPWAP® Signal matching
• iCAP® Real time signal matching
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Allowable Driving Stresses
Related to pile material strength
For Example, AASHTO provides the following limits:
• Steel Piles in Compresssion or Tension:
90% of Steel Yield Strength
• Prestressed Concrete Piles in Compression:
85% of concrete strength – Effective Prestress
• Prestressed Concrete Piles in Tension:
Prestress + 50% of concrete tensile strength
• Timber - Southern Pine/Douglas Fir:
3.2/3.5 ksi
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Damage Detection
Example Records for a Spliced Pile
Good Pile: No early reflection
Time of Impact
Toe Reflection
Time of Impact
Toe Reflection
Bad Pile: Splice should not cause an early reflection
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Toe Damage Detection: Early Record
24 inch PSC
L = 56 ft
WS 14,000 ft/sec
BN 220
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Toe Damage Detection: First indication
24 inch PSC
L = 56 ft
WS 14,000 ft/sec
BN 260
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Toe Damage Detection: End of Drive
24 inch PSC
L = 56 ft
WS 14,000 ft/sec
7 ft
BN
220
BN 1094 - EOD
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CAPWAP - “Signal Matching”
State-of-practice; required by specs/codes
We know both Input and Response
(wave down and wave up)
This is the information needed to calculate
static and dynamic soil model parameters
• Always (to be) used for capacity calculation
from dynamic load test
• Evaluates stresses vs. depth
• Models uniform or non-uniform piles
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I
R
Pile and Soil Model
Pile Segment
Impedance
Spring (static resistance), i.e.,
Capacity and Distribution
+ Soil Stiffness
Dashpot (dynamic resistance)
Zi = EiAi/ci
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CAPWAP Result Summary
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Toe Dynamic Resistance: Measured and CAPWAP
Grävare, 1980. “Pile Driving Construction Control by the Case Method” Ground Engineering.
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CAPWAP – Different Users, Static Test
+20%
SLT
-20%
CAPWAP
Case
Method
CAPWAP
CAPWAP Uniqueness? Pretty good
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CAPWAP: Comparison with Static Tests
CW versus SLT combined (N=303) (80, 96, SW)
Distribution of CW / SLT Ratios (96&SW: N=226)
25.0%
40,000
20.0%
Frequency
Unconservative
(potentially unsafe)
30,000
15.0%
10.0%
5.0%
CW [kN]
0.0%
0
4
-7
r7
70
de
n
u
9
4
9
-7
-8
-8
75
80
85
0
5
0
5
0
5
0
4
00
-9
13
10
11
11
12
12
13
-1
16161690
er
95
0
0
1
1
2
2
v
1
1
1
1
1
1
o
Ratio
20,000
Distribution of CW / SLTmax Ratios (96&SW: N=179)
25.0%
Conservative
(residual strength)
Frequency
20.0%
10,000
15.0%
10.0%
5.0%
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
0.0%
0
SLT [kN]
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Ratio
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=
=
=
=
=
Pile Top
Bottom
SC test data: T6P1 – 18 inch solid concrete pile
Static test (14D)
800
Ru
Rs
Rb
Dy
Dx
BOR 7 Day BN 4 (CAPWAP)
400
1.600
1.400
1.200
1.000
0.800
0.600
0.400
0.200
0.000
0
100
200
300
Load (kips)
500
600
700
Dynamic: 180 k
end bearing
Static: 176 k
end bearing
D is p la c e m e n t (in )
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Superposition:
When Restike is Done with Insufficient Energy
Thus not Activating Full End Bearing
30 inch
concrete pile
Length 65 ft
End of Drive
Blows/
foot
Max. Trans
Energy
Kip-ft
Static Capacity, Kips
Skin
Friction
End
Bearing
Total
Capacity
130
47
198
880
1078
Static Load Test
Restrike
1630
120
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Superposition
737
228*
965
737
880
1617
* Not fully activated (low energy)
Hussein, M., Sharp, M., Knight, W., “The Use of Superposition for Evaluating Pile Capacity”, Deep
Foundations 2002, An International Perspective on Theory, Design, Construction, and Performance,
Geotechnical Special Publication No. 116, American Society of Civil Engineers: Orlando, February, 2002
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Considering Soil Setup Capacity
St. Johns River Bridge:
Increased loads by 33%
with substantially shorter piles
(set-up considered)
Total project:
• $110 million (actual)
• $20 million (savings)
• $130 million (estimate)
Scales & Wolcott, FDOT, presentation at PDCA Roundtable
Orlando 2004
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®
iCAP
Signal matching program, executed during monitoring,
i.e., in real time, automatically, for immediate results.
Results:
• Total Capacity, with distribution
• Load test curve
• Compression stresses (max and toe)
• Tension stress maximum
• Also: Case Damping factor and Match Quality
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iCAP on PDA
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iCAP comparison with CAPWAP (2010)
Pipe Piles
H-Piles
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Concrete Piles
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PDA Testing of Vibratory Driven Piles
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PDA Testing of Vibratory Driven Piles
Measured - End of Driving
1500
1
0.8
1000
0.6
Force - kN
0.2
0
0
0
2
4
6
8
10
12
14
16
18
-500
20
-0.2
-0.4
-0.6
-1000
-0.8
-1500
-1
Time - L/c (3.7 ms)
Force
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Inertia
Velocity
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Velocity - m/s
0.4
500
PDA Testing of Vibratory Driven Piles
• Soil resistance calculated from
PDA force and velocity test
results based on either power or
force (Case Method) approach
• Unfortunately, soil reistance
and bearing capacity often differ
significantly, thus impact restrike
testing still necessary for dynamic
capacity evaluation
• GRLWEAP driveability
predictions reasonable but
sensitive to assumptions
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PDCA LRFD - 2000
Load and Resistance Factor Design
AASHTO (2010): φRn ≥ f1 Q1 + f2 Q2 + ….
Φ = 0.50
0.65
0.70
0.75
0.80
wave equation analysis (no testing)
2% or at least 2 dynamic tests
several DOTs specs - dynamic
static or 100% dynamic tests
static and 2% dynamic tests
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PDCA LRFD - 2000
Load and Resistance Factor Design
Example Calculation:
a) Assume 1.375 average load factor
b) Overall factor of safety: FS=1.375/φ
c) Assume Rn (nominal pile resistance)
of 200 kips
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PDCA LRFD - 2000
Load and Resistance Factor Design
Calculating
Overall safety factor and
No. of piles required for a 2000-kip load
Φ = 0.50 FS = 2.75
0.65
0.70
0.75
0.80
2.11
1.96
1.83
1.72
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Rn/FS=
(kips)
72 Npile= 28
95
21
102
20
109
18
116
17
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Reasons for Dynamic Pile Testing
• We spend a lot on deep foundations in the USA:
$4,000,000,000
• We want low risk of failure - remediation is
expensive
• We want safe bridges and other structures
• With LRFD less risk translates into less cost
• Testing allows for optimizing a foundation
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Summary: Pile Driving Analyzer
• Continuous improvements help obtain more
information faster (wireless, remote) and at
lower cost
• Test all pile types (steel, concrete, timber)
• Dynamic pile testing to supplement or replace
static load tests
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Summary: Pile Driving Analyzer
• Driving stress control to prevent damage
• Identify damaged piling
• Detect bad hammers for reliable application of
driving crieria
• Economical dynamic testing allows for more
tests and higher resistance factors
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Summary: CAPWAP
• CAPWAP test analysis for reliable capacity
prediction including resistance distribution and
end bearing
• 40 years experience; large database
• Capacity at time of testing (EOD or BOR) for
assessment of soil setup
• iCAP Signal Matching for operator independent
and immediate results
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Thanks for your attention
Frank Rausche
Pile Dynamics, Inc.
www.pile.com
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