2013 Louisiana Transportation Conference 1
Pile Driving Analyzer® (PDA) and CAPWAP®
Proven Pile Testing Technology: Principles and Recent Advances
Frank Rausche, Ph.D., P.E. ● 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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Our Objective: to provide the necessary methods, hardware and software for reliable quality assurance of
deep foundations
Pile Dynamics, Inc. - founded in 1972
2013 Louisiana Transportation Conference 4 1973
1982
1992
1965 1997
The Pile Driving Analyzer®
a long history of improvements
© 2012, Pile Dynamics, Inc.
2007
1958
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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• 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
Transducers Requirements
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2 D
Transducer Placement
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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• H-piles – no issue
• Pipe piles – use protectors
Sensor-Transmitter Protection
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• H-piles – no issue
• Pipe piles – use protectors
• Concrete piles – protectors
or - sensors in indentations
Sensor-Transmitter Protection
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Pile
S
ite
A
Pile
S
ite B
Pile Driving Analyzer
Engineer
- controls several PDAs
simultaneously as if on-site
- monitors piles in real time
- reports within short time
SiteLink® - Remote PDA
Contractor
- schedules easily
- keeps project going
USA Patent #6,301,551
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• 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
Design and Construction of Driven
Piles*
*See Hannigan et al., 2006. Manual on the Design and Construction of Driven Piles; FHWA
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Wave Equation Analysis (GRLWEAP)
Enter soil profile
Thermodynamic model predicts stroke for diesels
Predicts Driveability
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Wave Equation Analysis (GRLWEAP)
Updated hammer/driving system input
Refined capacity vs. blow count after testing
Updated soil parameters
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• 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
Dynamic Pile Testing Objectives
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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
Time of Impact Toe Reflection
Example Records for a Spliced Pile
Bad Pile: Splice should not cause an early reflection
Time of Impact Toe Reflection
Good Pile: No early reflection
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BN 220
Toe Damage Detection: Early Record 24 inch PSC L = 56 ft WS 14,000 ft/sec
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BN 260
Toe Damage Detection: First indication 24 inch PSC L = 56 ft WS 14,000 ft/sec
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BN 220
7 ft
24 inch PSC L = 56 ft WS 14,000 ft/sec
BN 1094 - EOD
Toe Damage Detection: End of Drive
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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
I R
• 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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Pile and Soil Model
Spring (static resistance), i.e.,
Capacity and Distribution
+ Soil Stiffness
Dashpot (dynamic resistance)
Pile Segment
Impedance
Zi = EiAi/ci
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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
CAPWAP CAPWAP Case
Method
SLT +20%
-20%
CAPWAP Uniqueness? Pretty good
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CW versus SLT combined (N=303) (80, 96, SW)
0
10,000
20,000
30,000
40,000
0 10,000 20,000 30,000 40,000
SLT [kN]
CW
[k
N]
Distribution of CW / SLT Ratios (96&SW: N=226)
0.0%
5.0%
10.0%
15.0%
20.0%
25.0%
unde
r 70
70-7
4
75-7
9
80-8
4
85-8
9
90-9
4
95-1
00
101-
105
106-
110
111-
115
116-
120
121-
125
126-
130
over
130
Ratio
Fre
qu
en
cy
Distribution of CW / SLTmax Ratios (96&SW: N=179)
0.0%
5.0%
10.0%
15.0%
20.0%
25.0%
unde
r 70
70-7
4
75-7
9
80-8
4
85-8
9
90-9
4
95-1
00
101-
105
106-
110
111-
115
116-
120
121-
125
126-
130
over
130
Ratio
Fre
qu
en
cy
CAPWAP: Comparison with Static Tests
Conservative
(residual strength)
Unconservative
(potentially unsafe)
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0100
200
300
400
500
600
700
800
0.0
00
0.2
00
0.4
00
0.6
00
0.8
00
1.0
00
1.2
00
1.4
00
1.6
00
Lo
ad
(kip
s)
Displacement (in)
Pile T
op
Bott
om
Ru
=
575.4
kip
s
Rs
=
395.4
kip
s
Rb
=
180.0
kip
s
Dy
=
0
.80 in
Dx =
1
.09 in
SC test data: T6P1 – 18 inch solid concrete pile BOR 7 Day BN 4 (CAPWAP) Static test (14D)
Dynamic: 180 k end bearing
Static: 176 k end bearing
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30 inch
concrete pile
Length 65 ft
Blows/
foot
Max. Trans
Energy
Kip-ft
Static Capacity, Kips
Skin
Friction
End
Bearing
Total
Capacity
End of Drive 130 47 198 880 1078
Static Load Test 1630
Restrike 120 27 737 228* 965
Superposition 737 880 1617
Superposition: When Restike is Done with Insufficient Energy
Thus not Activating Full End Bearing
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
* Not fully activated (low energy)
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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. Currently only for uniform DRIVEN PILES
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 comparison with CAPWAP (2010)
Pipe Piles H-Piles Concrete Piles
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PDA Testing of Vibratory Driven Piles
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
-1500
-1000
-500
0
500
1000
1500
0 2 4 6 8 10 12 14 16 18 20
Ve
loci
ty -
m/s
Forc
e -
kN
Time - L/c (3.7 ms)
Measured - End of Driving
Force Inertia Velocity
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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
AASHTO (2010): φRn ≥ f1 Q1 + f2 Q2 + ….
Φ = 0.50 wave equation analysis (no testing)
0.65 2% or at least 2 dynamic tests
0.70 several DOTs specs - dynamic
0.75 static or 100% dynamic tests
0.80 static and 2% dynamic tests
Load and Resistance Factor Design
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PDCA LRFD - 2000
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
Load and Resistance Factor Design
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PDCA LRFD - 2000
Calculating
Overall safety factor and
No. of piles required for a 2000-kip load
Load and Resistance Factor Design
Φ = 0.50 FS = 2.75 Rn/FS= 72 Npile= 28
0.65 2.11 (kips) 95 21
0.70 1.96 102 20
0.75 1.83 109 18
0.80 1.72 116 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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• 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
Summary: Pile Driving Analyzer
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• 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
Summary: CAPWAP
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