1. business and industrial
2. energy
3. electricity

Pile Acceptance – A System View
AGS
Perth, WA
12 May, 2015
Dr. Julian Seidel
Paper #1
Overview of The Role of Testing and
Monitoring in the Verification of
Driven Pile Foundations
ANZ 2015
Wellington, NZ
February, 2015
Dr. Julian Seidel
Talk Outline
1st Paper – Overview of Testing
• Static testing
• Dynamic testing
2nd Paper – Enhanced Use of PDA
• Dynamic Formulas (ECM)
• Pile Acceptance
Foundation Specialists Group
1 Introduction >
What is a system view?
• I care about the reliability of the single static or PDA test
• But I am more concerned about ensuring all 160 piles are OK
• My mind set is always – how can I ensure intent is met for all piles?
Foundation Specialists Group
Reconciling Test and System Perspectives
Heirarchy of Test Reliability
1. Static Testing
2. PDA Testing
3. Dynamic Formulas
Inopiles International Pte Ltd
Heirarchy of Project Influence
1. Dynamic Formulas
2. PDA Testing
3. Static Testing
Foundation Specialists Group
Static Load Testing
the good, the bad and the ugly
1 Introduction >
The reliability of design
• Pile design is uncertain
– prediction exercises
typically show a range
of 3 to 5 – highest to
lowest
• Testing is necessary
because of unreliability
of ground and
stratigraphic variations
Foundation Specialists Group
2 Pile Testing > 2.1 Static Load Testing > 2.1.1 Load Measurement
Static pile test : load measurement
• Static testing is the
‘golden reference‘ for pile
testing IF PERFORMED TO
A HIGH STANDARD
• Use of manometers
rather than load cells can
lead to capacity
overestimates of 20% or
more
Foundation Specialists Group
2 Pile Testing > 2.1 Static Load Testing > 2.1.2 Capacity Interpretation
Static pile test – capacity interpretation
• There is usually no definitive
and unequivocal
interpretation of a static
load test
• In this typical example, the
different interpretation
methods lead to a 25%
range of interpreted 'static
capacity'
Foundation Specialists Group
2 Pile Testing > 2.1 Static Load Testing > 2.1.3 Capacity Mobilization and Proof Tests
Mobilization : Proof vs Failure Tests
• If piles are tested to a
proof load rather than
geotechnical failure, then
the actual capacity can
only be inferred
• If the ultimate capacity is
uncertain, then the static
test is not a certain basis
for developing a capacityset relationship
Foundation Specialists Group
2 Pile Testing > 2.1 Static Load Testing > 2.1.4 Low Statistical Representation
Extrapolation of static testing – highway bridge
• 96 pier bridge
over flood plain
• 25m spans
• 16 piles/pier
• 0.5% = 1 pile every
12 spans or 300m
• 1% = 1 pile every
6 spans or 150m
Foundation Specialists Group
2 Pile Testing > 2.1 Static Load Testing > 2.1.4 Low Statistical Representation
Capacity variations and testing frequency
• In this example, capacities
in a single pier (5m x
12.6m) vary by 15%
about the average (all toes
within 0.2m penetration)
• How can the results of
static pile tests be
extrapolated distances of
150 to 300m?
Foundation Specialists Group
1.8m
2 Pile Testing > 2.1 Static Load Testing > 2.1.5 Time dependent capacity changes
The importance of time dependency
• Acceptance based on capacity, energy, set, TC at end of drive
• Static capacity at time of test may be more or less than the end of
drive capacity, so a relationship with set, TC is misleading
2,500
Capacity [kN]
2,000
1,500
capacity vs time
1,000
end of drive capacity
500
static capacity
0
0
1
10
100
1000
Foundation Specialists Group
10000 Time [days]
2 Pile Testing > 2.1 Static Load Testing > 2.1.5 Time dependent capacity changes
How to meaningfully use static?
• Basic problem : we need to control the DRIVING response of piles
based on results of tests conducted weeks after driving.
o
o
o
o
Static test to failure
Use load cells to accurately measure capacity
Adopt a 'reasonable' and consistent ultimate capacity interpretation –
probably displacement based
Recognize and accommodate time-dependency
• Correlate static and dynamic tests
• Establish setup or relaxation quantum and variability
Foundation Specialists Group
PDA Testing
the good, the bad and the ugly
1 Introduction >
How can PDA help?
1. Primarily it can be done extensively and spread around the site
2. But also it can be done at different times (EOID, Restrike)
3. It can be correlated UP to static testing and DOWN to driving
characteristics
Foundation Specialists Group
2 Pile Testing > 2.2 High Strain Dynamic Load Testing
PDA Testing
• Restrike Tests – allow time-dependence of capacity to be
established, and trends in post-installation capacity increase (setup)
or decrease (relaxation) to be taken into account for correlation
with reference static test
• Driving Tests – relate directly to driving criteria
and therefore allow linkage with typical acceptance criteria (EnergyCapacity-Movement relationship)
Pile SP38
Set = 0.9 mm/blow
TC = 6 mm
R = EMX
s + 0.5C
Foundation Specialists Group
2 Pile Testing > 2.1 Static Load Testing > 2.1.5 Time dependent capacity changes
The importance of time dependency
• Multiple PDA tests can establish time dependency trends
• PDA restrike tests can be performed just before or after a static test
(or both before and after) to better frame the comparison
2,500
Capacity [kN]
2,000
1,500
capacity vs time
1,000
PDA/CW capacity
500
static capacity
0
0
1
10
100
1000
Foundation Specialists Group
10000 Time [days]
2 Pile Testing > 2.2 High Strain Dynamic Load Testing > 2.2.1 Reliability of Dynamic Pile Tests
PDA/Capwap – a capacity INFERENCE
• Dynamic testing analysis by wave matching (e.g. Capwap) is based on
simple static/dynamic soil models. Capacity is INFERRED.
• The quality of the match reflects the relevance of the models to 'truth'
Measures
Type A
Type B
Type C
Occurrence
>95%
<5%
1%
Match Quality
Good
Good
Poor
Capacity Range
Narrow (< 10%)
Wide (> 20%)
Uncertain
Recommendation
Best Match or Upper
Bound
Lower Bound or Static
Correlation
Safe Lower Bound if it
can be assured
Static test to ultimate
capacity*
Optional
Yes, unless LB used
Yes
* Static testing to ultimate capacity is always best practice as long as requirements and limitations are understood
Foundation Specialists Group
2 Pile Testing > 2.2 High Strain Dynamic Load Testing > 2.2.1 Reliability of Dynamic Pile Tests
The reliability of Wave Matching analysis
14%
12%
10%
8%
1% DLT : 1/g = 1.77
16%
6%
4%
Chambers and Lehane (2011) : reduced 42 tests
2%
Likins and Rausche (2008) : 197 tests
1.975
1.925
1.875
1.825
1.775
1.725
1.675
1.625
1.575
1.525
1.475
1.425
1.375
1.325
1.275
1.225
1.175
1.125
1.075
1.025
0.975
0.925
0.875
0.825
0.775
0.725
0.675
0.625
0.575
0%
0.525
Relative Probability
18%
5% DLT: 1/g = 1.43
15% DLT : 1/g = 1.29
20%
10% DLT: 1/g = 1.33
• If static testing provides an accurate and relevant reference then
dynamic potentially overestimates by up to 30%
• This overestimate is 'covered' by a g of 0.75 [10% dynamic]
Ratio of dynamic: static (DLT / SLT)
Foundation Specialists Group
Geotechnical Credibility and Oversight
• The following 2 cases highlight the importance of analyses being
geotechnically informed
• They also highlight the importance of effective geotechnical
review and oversight
Foundation Specialists Group
Case 1 :Capwap vs Borelog near pile toe
Auto
Manual
Depth below
ground (m) Shaft/Toe (kPa) Shaft/Toe (kPa)
50.0
48.6
67.3
51.0
73.0
67.3
52.0
79.2
67.3
53.0
77.0
89.7
54.0
59.4
112.1
55.0
60.8
112.1
56.0
10.3
134.5
73
95
86
185
122
Foundation Specialists Group
4 Summary
Geotechnical credibility – Case 2
• Marine piling may require simultaneous assessment of tension,
compression and embedment for lateral capacity for pile sign-off
• Time for assessment and sign-off is critical
• Fast turnarounds are often specified
Foundation Specialists Group
5 Geotechnically credible solutions
Automatic vs "Geotechnical " Analysis
• With Auto matching the testing rate was increased to 100% of piles
• After Manual matching the testing rate was reduced back to 15% of piles
Auto
Foundation Specialists Group
Manual
5 Geotechnically credible solutions
Automatic vs "Geotechnical " Analysis
• For marine piles (uplift) shaft resistance is often critical
Manual
Auto
Total Capacity :
Shaft :
9700 – 17850 kN
3030 – 11313 kN
12300 – 15930 kN
8150 – 12550 kN
Foundation Specialists Group
4 Reliability through Solution Consistency
Consistency of solution
• If a consistent set of dynamic and static soil parameters can be
applied generally across a suite of tests, that modelling solution
gains greater credibility through the universality of its application
• A master database allows consistency of tests to be reviewed in
tables and graphs, e.g.
physical parameters
PDA parameters
Capwap parameters
Foundation Specialists Group
4 Summary
Summary – Paper 1
• Static testing is the reference test for a single pile test but is
hard to extrapolate
• On a project basis, static testing* can provide a reference or
calibration for dynamic tests
• A primary benefit of dynamic tests is they are extensive
• The inferred capacity error * is generally less than 10% (A) and
less than 25% (B), which is fully compensated by normal g
values
* if conducted properly
Foundation Specialists Group
Paper #2
Enhanced Use of Dynamic Pile Testing
in Foundation Engineering
ANZ 2015
Wellington, NZ
February, 2015
Dr. Julian Seidel
Dynamic Formulas
the good, the bad and the ugly
2 Pile Testing > 2.2 High Strain Dynamic Load Testing
PDA Testing
• Restrike Tests – allow time-dependence of capacity to be
established, and trends in post-installation capacity increase (setup)
or decrease (relaxation) to be taken into account for correlation
with reference static test
• Driving Tests – relate directly to driving criteria
and therefore allow linkage with typical acceptance criteria (EnergyCapacity-Movement relationship)
Pile SP38
Set = 0.9 mm/blow
TC = 6 mm
R = EMX
s + 0.5c
Foundation Specialists Group
Dynamic Formulas – comprehensively
discredited
•
•
•
•
Convention
Very low reliability
Use in sand and rock, not clay
Ratios to capacity vary within
and between sites
• Use as standalone for untested
piles anyway
Inopiles International Pte Ltd
• Comment
• Most studies pre 1980 against
static and before PDA
• Predict Driving Resistance
• Dynamic component of resistance
varies between sites and with
driving condition
• Use but use with understanding
(and correlation)
Foundation Specialists Group
3 Pile Monitoring
Pile Driving Monitor
•
•
•
•
Safe (from 10m) and accurate (0.1mm) measurement of set, TC
Measures position at 4000Hz
So pile velocity can be computed
Pile velocity is affected by hammer impact energy ( v   E )
3M disposable reflector
attached to pile
PDM 10m from pile
Foundation Specialists Group
3 Pile Monitoring
Variation in peak pile velocity
• The peak pile velocity
reflects variations in
hammer performance and
hammer and pile cushion
properties
• A variation in vpeak of
1.59 to 1.92 m/s suggests
a 45% variation in
delivered energy
R = EMX
s + 0.5c
Foundation Specialists Group
3 Pile Monitoring
Variation in delivered energy – concrete piles
• The same project
showed a variation of
-37%  +27% about
average for controlled
drop height
o
o
min 42.0 kJ
max 84.5 kJ
• Acceptance criteria
should adjust for
energies to individual
piles
Foundation Specialists Group
2 Inference of capacity from input and response
Inference of capacity
Apply and Measure
Input
Infer system
property
Dynamic Test :
Dynamic Test :
WaveDown
WaveUp
Static Test :
Static Test :
Load
Capacity (C)
Deflection
Untested :
Untested :
Stroke (E)
Measure Pile
Response
ECM Relationship
Foundation Specialists Group
Movement (M)
3 The Nexus between Energy Capacity and Pile Movement
Typical ECM Relationships
• Hiley Formula
R=
[Mm + n2(Mf + Mp)]
exMxh

Mm + Mf + Mp
s + 0.5(c1+c2+c3)
• Wave Equation (WE) Bearing Graph
R
E1
E2
E3

E1
R E
2
E3
1/set
Foundation Specialists Group
set
3 The Nexus between Energy Capacity and Pile Movement
The golden reference for the pile system
• Static load testing is the 'golden reference' for the evaluation of a single
pile capacity
• The Energy-Capacity-Movement relationship is the 'golden reference'
for the determination of the capacity of untested piles for a given
hammer-pile-foundation system
• Static testing is the reference for correlation of single dynamic tests
• The ECM relationship is the reference for development of a consistent
suite of dynamic tests.
• The ECM guides the installation of all untested piles (usu. 90%+)
Foundation Specialists Group
3 The Nexus between Energy Capacity and Pile Movement
Internally inconsistent PDA tests
• These tests are for same hammer, energy and pile
• The tests may suggest that capacity is 9500kN regardless of set
• Or that a set of 1.5mm achieves capacities between 9.7 and 14.6MN
Foundation Specialists Group
2 Pile Testing > 2.1 Static Load Testing > 2.1.4 Low Statistical Representation
Wave equation capacity-set relationships
• The tester provided WE bearing graphs matching each analyses
• At 8mm set, these curves suggest capacities between 3.8 and 9.8MN
• The tests don’t provide clarity for acceptance of untested piles in the
form of a consistent ECM relationship
Foundation Specialists Group
4 Summary
Pile capacity control - case study
• Marine piling is generally driven based on set or blow count alone
• Hence the bearing graphs just seen
• DRF = ECM Capacity / Reference Capacity
Foundation Specialists Group
5 Geotechnically credible solutions
Capacity-set trendline (Capwap vs set)
• There is a clear trend – but there is significant scatter. Why?
Foundation Specialists Group
5 Geotechnically credible solutions
Driving formula/Capwap trendline (DRF vs set)
• The trendline is developed from correlation of dynamic formula and Capwap
• The trend for the project is clear, with DRF increasing as set increases
Foundation Specialists Group
6 Isolated Test Approach and Quick Turnaround Analysis
The 1 hour Capwap analysis
• (Marine) Specifications sometimes require Capwap analysis in 1 hour
• This has unintended consequences ….
•
•
•
•
•
•
The 1 hour approach
Fast automatic analysis
No geotechnical input
No review of consistency
Project confusion
Reliance on individual tests
Sometimes (much) more testing
•
•
•
•
•
•
The ECM approach
(Slow) manual analysis
Geotechnically informed
Consistent parameters, results
Clear project guidance
Sign-off on project-wide basis
Relatively less testing
Foundation Specialists Group
Piling Targets and Real-time sign-off
Foundation Specialists Group
8 Implementation of a System Approach
Implementing an ECM System Approach
• Recognize that Capwap is not unique (5-10% generally and < 25%)
• First 5 or 6 Capwap analyses are considered draft
• Establish the ECM relationship based on the initial analyses
(correlated dynamic formula, suite of bearing graphs etc.)
• Adjust and re-issue the 5 or 6 initial Capwap analyses with consistent
parameters that support the ECM
• ALL piles (tested or untested) are accepted by the ECM and whatever
other criteria are required for conformance (zero delay << 1hour!)
• Ongoing review of ECM relationship
Foundation Specialists Group
8 Implementation of a System Approach
The need for monitoring of every pile
Steel pile with modern hydraulic hammer
400
Measured Energy EMX
350
300
308
301
281
297
17
18
19
20
370
310
16
265
305
15
323
12
303
308
11
14
305
10
274
308
360
8
9
375
7
321
5
297
330
306
4
150
317
200
380
250
100
50
Foundation Specialists Group
Sequence of dynamic tests
22
21
13
6
3
2
0
1
Measured Energy (kJ)
• Effective Monitoring of
energy and movement
• Energy variations even for
hydraulic hammer on steel
piles varies -16% to +20%
about average
• All piles are as important
as each other, whether
tested or not
3 Pile Monitoring
QA/Capacity estimation for untested piles
• Pile Driving Monitor (PDM) combined and correlated with PDA /
Capwap for reliable energy capacity and movement estimation for
all untested piles
PDM in use offshore in Mauritius for both continuous driving records and final capacity assessment
Foundation Specialists Group
4 Summary
Summary – Paper 2
• PDA/Capwap should be mindful and geotechnically informed
• Automatic Capwap analysis does not meet either criterion
• Reviewers should do credibility checks on both individual Capwaps
and on the suite of results
• Mindless analysis can misinform and lead to increased testing
• A system approach based on establishing the underlying ECM
relationship is recommended
• Such an approach will provide an informed and consistent
assessment, clear guidance, and faster sign-off.
Foundation Specialists Group
Thank you
Questions?
AGS
Perth, WA
12 May, 2015
Dr. Julian Seidel