1. High Strain Pile Testing with the Pile Driving
Analyzer System® (PDA)and CAPWAP®
PDA Wave Mechanics 1
Outline
• Introduction
– Measurement Evaluation
– Forces and Stresses in Pile
– Integrity
– Bearing capacity
– Examples
• Summary
• Problems
PDA Wave Mechanics 2
Measuring strain and acceleration
at one point
Strain transducer Accelerometer
PDA Wave Mechanics 3
2. Alternative force transducer or F=ma
For F=ma or top load cell
testing, accelerometers must
be attached to pile top.
PDA Wave Mechanics 4
PDA testing and data acquisitionPDA testing and data acquisition
After securely
attaching sensors to
pile, it is important to
input the pertinent
and latest calibration
values in PDA
PDA Wave Mechanics 5
Measurements on a follower, nearshore
PDA Wave Mechanics 6
3. The Pile Driving Analyzer - Model 8G
• Measures force and
velocity, usually near
the pile top, but also
at other locations
such as the pile toe.
• Determines Case
Method resistance,
iCAP®, energy
transferred to pile
and stresses in pile
PDA and CAPWAP 7
Site Link® for Remote Monitoring
Reduces travel cost and scheduling problems
Site Link® for Remote Monitoring
Reduces travel cost and scheduling problems
PDA and CAPWAP 8
Acceleration and Strain vs. TimeAcceleration and Strain vs. Time
Accelerometers, one on each
side; acceleration, velocity,
displacement
Strain Transducers, one on
each side; yield strain, stress
and average force
PDA Wave Mechanics 9
4. ●
Compressive stresses, forces: FMX, CSX, CSI
PDA Wave Mechanics 10
●CSX = 233 MPa (33.8 ksi)
FMX = 1280 kN
●CSX = 233 MPa (33.8 ksi)
FMX = 1280 kN
●
● ●CSI = 245 MPa (35.5 ksi)
For H-piles, Load Cell or F=ma Measurements: no CSI
PDA Wave Mechanics 11
Compressive stresses, forces: FMX, CSX, CSI
Force, Velocity, DisplacementForce, Velocity, Displacement
FMX
DMX = ½ max (d1 + d2)
DFN = ½ (d1 fin + d2 fin)
d2(t) = ∫v2(t) dt
d1(t) = ∫v1(t) dt
d1 max
PDA Wave Mechanics 12
d1 fin
d2 fin
5. Pile top force and velocity from PDAPile top force and velocity from PDA
We are measuring the total force and the total velocity
We plot both together using Z to scale velocity
We are measuring the total force and the total velocity
We plot both together using Z to scale velocity
F(t) = ½ A E [ε1(t) + ε2(t)]
v(t) = ½ [v1(t) + v2(t)] Z
PDA Wave Mechanics 13
Fu = - vu (EA/c)Fu = - vu (EA/c)
u = - vu (E/c)u = - vu (E/c)
εu = - vu / cεu = - vu / cεd = vd / cεd = vd / c
d = vd (E/c)d = vd (E/c)
Fd = vd (EA/c)Fd = vd (EA/c)
If wave travels
“downwards”
If wave travels
“upwards”
PDA Wave Mechanics 14
Superposition of WavesSuperposition of Waves
Fd=ZvdFd=Zvd
Downward Waves
Fu=-ZvuFu=-Zvu
Upward Waves
F = Fd + Fu
v = vd + vu
PDA Wave Mechanics 15
6. Wave Down and Wave Up from F and Zv
Fd=½(F+Zv) Fu=½(F-Zv)
Fd or Wd; Fu or Wu
Fd1 or Wd1
Fd2 or Wu2
PDA Wave Mechanics 16
If we know wave up and wave down
We can calculate
Pile forces at other locations
If we know wave up and wave down
We can calculate
Pile forces at other locations
The force at any point along the pile length can be
determined from the superposition of the forces in
the upward traveling and downward traveling waves
The force at any point along the pile length can be
determined from the superposition of the forces in
the upward traveling and downward traveling waves
F = Fu + FdF = Fu + Fd
PDA Wave Mechanics 17
L
2L/ct = 0 L/c
Upward
Wave
Upward
Wave
Downward
Wave
Downward
Wave
Wave Superposition for Force below SensorsWave Superposition for Force below Sensors
X
Fd1
Fu2
Fx = Fu2 + Fd3
Fd3
2x/c
PDA Wave Mechanics 18
7. TopToe
t3
Tension Stress Calculation – Wave-UpTension Stress Calculation – Wave-Up
Point of max tension
min Fu
min Fu
PDA Wave Mechanics 19
Pile Damage: BTA, LTD
LTD
•A reduction of pile impedance (Z)
above the pile toe causes a tension
reflection before 2L/c
•The time at which the tension
reflection arrives at the gage location
indicates the depth to Z-reduction:
LTD = (tdamage / 2) c
•The magnitude of the Z-reduction is
calculated with the -formula
PDA Wave Mechanics 21
t1
t3
Fu,1 = ½(Ft3-Zvt3)
Fd,1 = ½(Ft1+Zvt1)
Damage Example
PDA Wave Mechanics 22
8. PDA Capacity Monitoring
The 1965 (Phase 1) equation was based on a
rigid body model: Ru = F(to) - mp a(to)
Time to is time of zero velocity – no damping
to
PDA Wave Mechanics 23
But then we derived the 1968 Case Method
Resistance Waves
L/c
L
x
Ri
-½Ri
RB
RB
Upward traveling wave at time 2L/c:
Fu,2 = -Fd,1 + ½Ri + ½Ri + RB
RTL = Fu,2 + Fd,1
Fd,1
-Fd,1
½Ri
PDA Wave Mechanics 24
½Ri
RD = Jv vtoe = Jc Z vtoeRD = Jv vtoe = Jc Z vtoe
Calculated Damping Component
The Case Method
uses the pile toe velocity for damping calculations; it is
affected by shaft and toe soil resistance!
Calculated Damping Component
The Case Method
uses the pile toe velocity for damping calculations; it is
affected by shaft and toe soil resistance!
PDA Wave Mechanics 25
Jv … viscous damping factor [kN/m/s]
Jc … the dimensionless Case Damping Factor
vtoe = (2Fd1 – RTL)/Z based on wave mechanics
9. Case Method Static Resistance
Rstatic= RTL - RD
Rstatic= Fu,2 + Fd,1 - Jc(2 Fd,1 – Fd1 – Fu,2)
Rstatic= (1 – Jc)Fd,1 + (1 + Jc )Fu,2
Total Resistance = Static + Dynamic ResistanceTotal Resistance = Static + Dynamic Resistance
PDA Wave Mechanics 26
Fd,1 = 5,450 kN
Fu,2 = 2,730 kN
Rstatic = (1 – Jc) Fd,1+ (1 + Jc) Fu,2Rstatic = (1 – Jc) Fd,1+ (1 + Jc) Fu,2
RTL = 5,450 + 2,730 = 8,180 kN
For example with Jc= .3
Rstatic = (1 - .3) 5,450 + (1 + .3) 2,730 = 7,350 kN
RTL = 5,450 + 2,730 = 8,180 kN
For example with Jc= .3
Rstatic = (1 - .3) 5,450 + (1 + .3) 2,730 = 7,350 kN
PDA Wave Mechanics 27
Maximum Case Method Resistance, RXiMaximum Case Method Resistance, RXi
t1 t2
2L/c
Calculates Rstatic
at all times after
the first velocity
peak
Selects the
maximum Rstatic
for JC= 0.i
Calculates Rstatic
at all times after
the first velocity
peak
Selects the
maximum Rstatic
for JC= 0.i
PDA Wave Mechanics 28
10. Shaft and Toe Resistance
2L/ct = 0 L/c
L
x
R
-½R
RB
½R
RB
Fd,1 -Fd,1
½R
PDA Wave Mechanics 29
Ri - Wave upRi - Wave up
R
½R
PDA Wave Mechanics 30
An Example: PDA Capacity Results
End of Driving
PDA Wave Mechanics 31
12. PEBWAP for and End Bearing Pile
20x0.5” OEP; LG = 22.3 m; D46-32; 0.6 mm/bl; JC = 0.3
0
1500
3000
4500
6000
7500
0 5 10 15
Resistance-kN
Toe Displacement - mm
Total Resistance Static Resistance
Static Resistance = Total Resistance – Damping Factor * Toe Velocity
PDA and CAPWAP 35
THE CAPWAP METHODTHE CAPWAP METHOD
1 Set up pile and soil model and assume
Rshaft and Rtoe
1 Set up pile and soil model and assume
Rshaft and Rtoe
Rshaft
Rtoe
5 If no satisfactory match: Go to Step 25 If no satisfactory match: Go to Step 2
4 Adjust Rshaft and Rtoe4 Adjust Rshaft and Rtoe
3 Compare WUC with measured WUM3 Compare WUC with measured WUM
2 Apply measured WDM to pile model at top and
calculate complementary WUC
2 Apply measured WDM to pile model at top and
calculate complementary WUC
WUM
WDM
WUC
PDA and CAPWAP 36
First try (poor)
Final match (good)
Adjustments
CAPWAP is an
Iterative Process
PDA and CAPWAP 37
13. Seg. i
∆Li
Ri
Fdo
i
Fdn
i
Fun
i
Fuo
i
Rdi
Rui
The Pile is divided in Np
uniform pile segments of
approximately 1 m length.
Segment lengths are chosen
for equal time increment
∆t = ∆Li/ci.
Each Segment has:
impedance Zi,,= EiAi/ci ,
mass mi = Zi ∆t and
stiffness ki = Zi/∆t .
The Pile Model
PDA and CAPWAP 38
The Combined CAPWAP Pile and Soil ModelThe Combined CAPWAP Pile and Soil Model
Soil segment length:
LSi = Nfac Li
Soil segment length:
LSi = Nfac Li
Spring (static resistance)
Dashpot (dynamic resistance)
Spring (static resistance)
Dashpot (dynamic resistance)
t
t
t
t
t
t
t
Pile Model:
Impedance Zi
= EiAi/ci
Pile Segment
Length Li
Wave Travel
time in Pile
t = Li/ci
Pile Model:
Impedance Zi
= EiAi/ci
Pile Segment
Length Li
Wave Travel
time in Pile
t = Li/ci
PDA and CAPWAP 39
Rui, qi
Rt, qt
Ji
JT Shaft Resistance,
Ns times
Shaft Resistance,
Ns times
tG
The Basic
CAPWAP
Soil Model
The Basic
CAPWAP
Soil Model
End
Bearing
End
Bearing
PDA and CAPWAP 40
14. mt
Rui, qi
Rt, qt
Ji
JT
JSK
JBT
Add Radiation Damping
Inertia Resistance
Add Radiation Damping
Inertia Resistance
tG
ms
mPL
Some
CAPWAP
Soil Model
Extensions
Some
CAPWAP
Soil Model
Extensions
mSP
PDA and CAPWAP 41
Signal Matching ExampleSignal Matching Example
PDA and CAPWAP 42
First Trial Analysis (Lousy Match)First Trial Analysis (Lousy Match)
Input F
Matching F
Input F
Matching v
or
Input v
Matching F
or
PDA and CAPWAP 43
16. CAPWAP Help FeaturesCAPWAP Help Features
HC
CAPWAP Variable Help
HC
CAPWAP Variable Help
HR
CAPWAP Resistance
vs Displacement Help
HR
CAPWAP Resistance
vs Displacement Help
PDA and CAPWAP 47
CAPWAP’s
Static Pile and
Soil Model
CAPWAP’s
Static Pile and
Soil Model
kshaft, I = Ru,i
/qi
ktoe, i
Ru, i
kp, i
Rtoe, i
Q
u
1
uto
e
PDA and CAPWAP 48
CAPWAP Static AnalysisCAPWAP Static Analysis
The final static
load
displacement
curve is from a
t-z and q-z
analysis
The final static
load
displacement
curve is from a
t-z and q-z
analysis
PDA and CAPWAP 49
17. CAPWAP Static
Analysis
Options
CAPWAP Static
Analysis
Options
Smoothing
User Capacity
Uplift Test
Extrapolation
Failure Criteria
Smoothing
User Capacity
Uplift Test
Extrapolation
Failure Criteria
PDA and CAPWAP 50
Standard OutputStandard Output
PDA and CAPWAP 51
Comprehensive CAPWAP ReportComprehensive CAPWAP Report
• “Blow Count” is
from Direct Input in
CAPWAP or from
PDA-W
• “Job Information”
provides for other
information input
PDA and CAPWAP 52
18. Summary
Table Output
Summary
Table Output
Ri, qi, Ji
PDA and CAPWAP 53
Numerical
Output
Numerical
Output
Case Method
Extrema
PDA and CAPWAP 54
TAMPA DRILLED SHAFT TESTING
PDA and CAPWAP 55
19. Instrumentation
PDA and CAPWAP 56
CAPWAP Results for several blows
APE 750; 60 ton ram (2.4% of test load = 2470 tons). Four blows; 4.5 ft drop; 6 ft dia. shafts;
(under pier) in limestone
see: Rausche, Likins, Hussein, (2008). GSP #180, ASCE
Proposed failure criterion for dynamic tests for the cumulative toe
displacement:
D/60
60 ton ram was 2.4% of failure load
2500 ton failure load
72” dia shaft; Cooper Marl
Large diameter shaft in soil
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 1000 2000 3000 4000 5000 6000
PileTopDisplacement(in)
Pile Top Load (Kips)
Blow 3 = 2.5 FT Stroke Blow 4 = 4.0 FT Stroke
Blow 5 = 5.0 FT Stroke Elastic Line
PDA and CAPWAP 58
20. CAPWAP Comparisons
with Static Load Tests – H-Pile
H-pile 14x73 (356 x 109);
Penetration 45 m
Soil: Silts and clays with N<15
for depths < 30 m, then clays
and silts with 40<N<100 to 45 m.
Hammer: D30-32
EOD: 8 mm set/blow
BOR: 5 mm set/blow
EOR: 15 mm set/blow
CAPWAP 21-day Restrike (Blow 2): Ru=2060 kN; (Blow 25): Ru=1600 kN
Static Load Test (48 days): 2000 kN; Rausche, Likins, Hussein, 2008.
PDA and CAPWAP 59
Florida Drilled ShaftFlorida Drilled Shaft
Diameter:
• to 20 ft (6.1m) 28” (710mm)
• to 44 ft (13.4m) 24” (610mm)
• Soil: Shaft: Sand
Toe: Soft Limestone.
• Hammer: 10 tons
Hussein et al., 1992
6.1 m
13.4 m
Toe 2
Toe
Shaft
Shaft
Note:
Toe 2 treatment much simplified in
CAPWAP 2014
PDA and CAPWAP 60
Florida Drilled Shaft: Class A PredictionFlorida Drilled Shaft: Class A Prediction
• Required Rult:
1000 kips (4450 kN)
• Static and dynamic
tests indicate a
capacity less than
760 kips (3380 kN),
depending on criterion
3560 kN
• Offset Criterion yields
650 kips (2890 kN)
from static and
dynamic test.
PDA and CAPWAP 61
21. CAPWAP Correlation:
Automatic Procedure
CAPWAP Correlation:
Automatic Procedure
PDA and CAPWAP 62
CAPWAP Correlation:
Radiation Damping Model
CAPWAP Correlation:
Radiation Damping Model
PDA and CAPWAP 63
Combined Data Bases of GRL 1996
and from Stress Wave Conferences
Mean: 0.98; COV: 0.17; N = 303
Likins and Rausche, 2004
PDA and CAPWAP 64
22. CAPWAP Critique - iCAP Features
• CAPWAP is Non-unique?
Just one result!
• CAPWAP is Slow?
Real time result!
• CAPWAP needs Experience?
Done by PDA Operator!
PDA and CAPWAP 65
iCAP Application
• When?
– During Monitoring
– During Restrike
– During Reanalysis
• When Not?
– When pile and/or soil properties are not well known
– Problem data which lead to poor matches
• How?
– Just turn it on
• Notes:
– iCAP can be run directly from CAPWAP-2014 for non-
uniform piles
– iCAP is no CAPWAP; differences must be expected;
review is recommended
66PDA and CAPWAP 66
Summary
• PDA Testing During Driven Pile installation,
called monitoring, checks driving stresses, pile
integrity, resistance at the time of testing
• Performing a resike test after waiting yields a
dynamic load test.
• Case Method closed form measurements
together with stress wave considerations yield
information on
– dynamic stresses
– pile integrity
– bearing capacity
PDA Wave Mechanics 67
