1. 4/18/2015
1
Bengt H. Fellenius
The Static Loading Test
Performance, Instrumentation, Interpretation
2
A routine static loading test provides
the load-movement of the pile head...
and the pile capacity?
2. 4/18/2015
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3
The Offset Limit Method
Davisson (1972)
OFFSET (inches) = 0.15 + b/120
OFFSET (mm) = 4 + b/120
b = pile diameter
L
L
EA
Q
Q
L
Tom Davisson determined this definition as the one that fitted
best to the capacities he intuitively determined from a FWHA
data base of loading tests on driven piles. The definition does
not mean or prove the the pile diameter has anything to do with
the interpretation of capacity from a load-movement curve.
4
The Decourt Extrapolation
Decourt (1999)
0 100 200 300 400 500
0
500,000
1,000,000
1,500,000
2,000,000
LOAD (kips)
LOAD/MVMNT--Q/s(inch/kips)
Ult.Res = 474 kips
Linear Regression Line
0.0 0.5 1.0
0
100
200
300
400
500
MOVEMENT (inches
LOAD(kips)
Q
1
2
C
C
Qu
C1 = Slope
C2 = Y-intercept
Q
Ru = 470 kips – 230 tons
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5
Other methods are:
The Load at Maximum Curvature
Mazurkiewicz Extrapolation
Chin-Kondner Extrapolation
DeBeer double-log intersection
Fuller-Hoy Curve Slope
The Creep Method
Yield limit in a cyclic test
For details, see Fellenius (1975, 1980)
6
CHIN and DECOURT 235
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7
A rational, upper-limit definition to use for “capacity” is the load that
caused a 30-mm pile toe movement.
Indeed, bringing the toe movement into the definition is the point. A
“capacity” deduced from the movement of the pile head in a static loading
test on a single pile has little relevance to the structure to be supported by
the pile. The relevance is even less when considering pile group response.
0
1,000
2,000
3,000
4,000
0 10 20 30 40 50 60 70 80
LOAD(kN)
MOVEMENT (mm)
OFFSET LIMIT
LOAD 2,000 kN
Shaft
Head
Toe
Compression
LOAD = 3,100 kN
for 30 mm toe
movement
8
0
500
1,000
1,500
2,000
2,500
0 5 10 15 20 25 30 35 40
MOVEMENT (mm)
LOAD(KN)
Offset-
Limit
Line
Definition of capacity (ultimate resistance) is only needed
when the actual value is not obvious from the load-
movement curve. However, the below test result is rare.
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9
What really do we learn from
unloading/reloading and what
does unloading/reloading do to
the gage records?
10
Result on a test on a 2.5 m diameter, 80 m long bored pile
Does unloading/reloading add anything of value to a test?
0
5
10
15
20
25
30
0 25 50 75 100 125 150 175 200
MOVEMENT (mm)
LOAD(MN)
Acceptance Criterion
0
5
10
15
20
25
30
0 25 50 75 100 125 150 175 200
MOVEMENT (mm)
LOAD(MN)
Acceptance Criterion
Repeat test
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11
Plotting the repeat test in proper sequence
0
5
10
15
20
25
30
0 25 50 75 100 125 150 175 200
MOVEMENT (mm)
LOAD(MN)
Acceptance Criterion Repeat test plotted in
sequence of testing
The Testing Schedule
0
50
100
150
200
250
300
0 6 12 18 24 30 36 42 48 54 60 66 72
TIME (hours)
"PERCENT"
A much superior test schedule. It presents a large number of values (≈20 increments), has no
destructive unloading/reload cycles, and has constant load-hold duration. Such tests can be used
in analysis for load distribution and settlement and will provide value to a project, as opposed to the
long-duration, unloading/reloading, variable load-hold duration, which is a next to useless test.
Plan for 200 %, but make use of
the opportunity to go higher if
this becomes feasible
The schedule in blue is typical for many standards. However, it is costly, time-consuming,
and, most important, it is diminishes or eliminates reliable analysis of the test results.
XXXXX
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13
0
200
400
600
800
1,000
0 1 2 3 4 5 6 7
MOVEMENT (mm)
LOAD(KN)
ACTIVE
PASSIVE
Caputo and Viggiani (1984) with data from Lee and Xiao (2001).
Load-Movement curves from static loading tests on two
“ACTIVE” piles (one at a time) and one “PASSIVE”.
.
Diameter, b = 400 mm; Depths = 8.0 m and 8.6 m. The
“PASSIVE” piles are 1.2 m and 1.6 m away from the
“ACTIVE” (c/c = 3b and 4b).
0
400
800
1,200
1,600
2,000
0 4 8 12 16 20 24
MOVEMENT (mm)
LOAD(KN)
ACTIVE
PASSIVE
Load-Movement curves from static loading tests on one
pile (“ACTIVE”). Diameter (b) = 500 mm; Depth = 20.6 m.
“PASSIVE” pile is 3.5 m away (c/c = 7b).
Pile Interaction
CASE 1 CASE 2
14
0
200
400
600
800
0 2 4 6 8 10
PILE HEAD MOVEMENT (mm)
LOADPERPILE(KN)
Single Pile
Average of 4 Piles
Average of 9 Piles
O’Neill et al. (1982)
Group Effect
20 m
Single Pile
9-pile Group
4-pile Group
Comparing tests on single pile, a 4-pile group, and a 9-pile group
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15
Data from Phung, D.L (1993)
2.30m
800mm
800 mm
60 mm
#1
#2 #3
#4 #5
Loading tests on a single pile and a group of 5 piles in loose,
clean sand at Gråby, Sweden.
Pile #1was driven first and tested
as a single pile. Piles #2 - #5 were
then driven, whereafter the full
group was tested with pile cap not
in contact with the ground.
16
Data from Phung, D.L (1993)
0
2
4
6
8
10
12
14
16
0 5 10 15 20 25 30 35 40 45 50
MOVEMENT OF PILE HEAD (mm)
LOAD/PILE(KN)
Average
Single
#2
#5
#4
#3
#1
#1
2,3 m
340 mm
#2
#3 #4
#5
800 mm
First test: Pile #1 as a single pile. Second test (after driving Piles #2 - #5):
Testing all five piles with measuring the load on each pile separately.
#1
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17
Data from Phung, D.L (1993)
0
2
4
6
8
10
12
14
16
0 10 20 30 40 50 60 70 80
MOVEMENT OF PILE HEAD (mm)
LOAD/PILE(KN)
Pile #1 reloaded as
part of the group after
Piles #2 - #5 were
driven
#1
#1
Pile #1: Effect of compaction caused by driving Piles #2 through #5 and then testing #1 again
18
Instrumentation
and
Interpretation
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19
T e l l t a l e s
• A telltale measures shortening of a pile and must never be arranged to
measure movement.
• Let toe movement be the pile head movement minus the pile shortening.
• For a single telltale, the shortening divided by the distance between
the pile head and the telltale toe is the average strain over that length.
• For two telltales, the distance to use is that between the telltale tips.
• The strain times the cross section area of the pile times the pile material
E-modulus is the average load in the pile.
• To plot a load distribution, where should the load value be plotted?
Midway of the length or above or below?
20
Load distribution for constant unit shaft resistance
Unit shaft resistance
(constant with depth)
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21
Linearly increasing unit shaft resistance
and its load distribution
DEPTH
LOAD IN THE PILE
DEPTH
SHAFT RESISTANCE
DEPTH
UNIT RESISTANCE
x = h/√2
h/2
A1
A2
x = h/√2
h
ah
ah2/2
ah2/20
0
0
0
"0"
ah
TELLTALE 0 ShaftResistance
Resistance
at TTL Foot
Telltale Foot
Linearly increasing unit
shaft resistance 2
5.0
2
22
ahax
2
h
x ===>21 AA ===>
x
22
• Today, telltales are not used for determining strain (load) in a pile
because using strain gages is a more assured, more accurate, and
cheaper means of instrumentation.
• However, it is good policy to include a toe-telltale to measure toe
movement. If arranged to measure shortening of the pile, it can also be
used as an approximate back-up for the average load in the pile.
• The use of vibrating-wire strain gages (sometimes, electrical
resistance gages) is a well-established, accurate, and reliable means
for determining loads imposed in the test pile.
• It is very unwise to cut corners by field-attaching single strain gages to
the re-bar cage. Always install factory assembled “sister bar” gages.
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Rebar Strain Meter — “Sister Bar”
Reinforcing Rebar
Rebar Strain Meter
Wire Tie
InstrumentCable
or Strand
Wire Tie
Tied to Reinforcing Rebar Tied to Reinforcing Rings
Reinforcing Rebar
or Strand
(2 places)
Rebar Strain Meter
InstrumentCables
(3 places,120° apart)
Hayes 2002
Three
bars?!
Reinforcing Rebar
Rebar Strain Meter
Wire Tie
InstrumentCable
or Strand
Wire Tie
Tied to Reinforcing Rebar Tied to Reinforcing Rings
Reinforcing Rebar
or Strand
(2 places)
Rebar Strain Meter
InstrumentCables
(3 places,120° apart)
13. 4/18/2015
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25
0
2
4
6
8
10
12
14
16
18
20
0 50 100 150 200
STRAIN (µε)
LOAD(MN)
Level 1A+1C
Level 1B+1D
Level 1 avg
Load-strain of individual gages and of averages
0
2
4
6
8
10
12
14
16
18
0 100 200 300 400 500 600 700
STRAIN (µε)
LOAD(MN)
LEVEL 1 D CA B
A&C B&D
The curves are well together and
no bending is discernible
Both pair of curves indicate bending; averages are very close;
essentially the same for the two pairs
PILE 1 PILE 2
26
If one gage “dies”, the data of surviving single gage should be discarded.
It must not be combined with the data of another intact pair.
Data from two surviving single gages must not be combined.
0
2
4
6
8
10
12
14
16
18
20
0 100 200 300 400 500 600 700
STRAIN (µε)
LOAD(MN)
A&C+D
Means: A&C, B&D, AND A&B&C&D
A&C+B
D B+CA+D
LEVEL 1
Error when including
the single third gage, when
either Gage B or Gage D data
are discarded due to damage.
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27
Hanifah, A.A. and Lee S.K. (2006)
Glostrext Retrievable Extensometer (Geokon 1300 & A9)
Anchor arrangement display Anchors installed
Geokon borehole extensometer
28
Gage for measuring
displacement, i.e., distance
change between upper and
lower extensometers.
Accuracy is about 0.02mm/5m
corresponding to about 5 µε.
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29
That the shape of a pile sometimes can be quite different from the straight-
sided cylinder can be noticed in a retaining wall built as a pile-in-pile wall
30
0
5
10
15
20
25
0.00 0.50 1.00 1.50 2.00 2.50
DIAMETER RATIO AND AREA RATIO
DEPTH(m)
Gage
Depth
Diameter
Ratio
Area
Ratio
O-cell
Nominal
Ratio
Determining actual shape of the bored hole before concreting
Bidirectional cell
Data from Loadtest Inc.
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31
We have got the strain.
How do we get the load?
• Load is stress times area
• Stress is Modulus (E) times strain
• The modulus is the key
E
32
For a concrete pile or a concrete-filled bored pile, the
modulus to use is the combined modulus of concrete,
reinforcement, and steel casing
cs
ccss
comb
AA
AEAE
E
Ecomb = combined modulus
Es = modulus for steel
As = area of steel
Ec = modulus for concrete
Ac = area of concrete
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33
• The modulus of steel is 200 GPa (207 GPa for those weak at heart)
• The modulus of concrete is. . . . ?
Hard to answer. There is a sort of relation to the cylinder strength and the
modulus usually appears as a value around 30 GPa, or perhaps 20 GPa or
so, perhaps more.
This is not good enough answer but being vague is not necessary.
The modulus can be determined from the strain measurements.
Calculate first the change of strain for a change of load and plot the
values against the strain.
Values are known
tE
34
0 200 400 600 800
0
10
20
30
40
50
60
70
80
90
100
MICROSTRAIN
TANGENTMODULUS(GPa)
Level 1
Level 2
Level 3
Level 4
Level 5
Best Fit Line
Example of “Tangent Modulus Plot”
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35
ba
d
d
Et
b
a
2
2
sE
Which can be integrated to:
But stress is also a function of
secant modulus and strain:
Combined, we get a useful relation:
baEs 5.0
In the stress range of the static loading test, modulus of concrete is
not constant, but a more or less linear relation to the strain
and Q = A Es ε
36
0 200 400 600 800
0
10
20
30
40
50
60
70
80
90
100
MICROSTRAIN
TANGENTMODULUS(GPa)
Level 1
Level 2
Level 3
Level 4
Level 5
Best Fit Line
Example of “Tangent Modulus Plot”
Intercept is
”b”
Slope is “a”
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37
Note, just because a strain-gage has registered some strain
values during a test does not guarantee that the data are useful.
Strains unrelated to force can develop due to variations in the pile
material and temperature and amount to as much as about 50±
microstrain. Therefore, the test must be designed to achieve
strains due to imposed force of ideally about 500 microstrain and
beyond. If the imposed strains are smaller, the relative errors and
imprecision will be large, and interpretation of the test data
becomes uncertain, causing the investment in instrumentation to
be less than meaningful. The test should engage the pile material
up to at least half the strength. Preferably, aim for reaching close
to the strength.
38
The secant stiffness approach can only be applied to
the gage level immediately below the pile head (must
be uninfluenced by shaft resistance), provided the
strains are uninfluenced by residual load.
Field Testing and Foundation Report, Interstate H-1, Keehi
Interchange, Hawaii, Project I-H1-1(85), PBHA 1979.
y = -0.0014x + 4.082
0
1
2
3
4
5
0 500 1,000 1,500 2,000
STRAIN (µε)
TANGENTSTIFFNESS,∆Q/∆ε(GN)
TANGENT STIFFNESS, ∆Q/∆ε
y = -0.0007x + 4.0553
0
1
2
3
4
5
0 500 1,000 1,500 2,000
STRAIN (µε)
SECANTSTIFFNESS,Q/ε(GN)
Secant Data
Secant from Tangent Data
Trend Line
SECANT STIFFNESS, Q/ε
Strain-gage instrumented, 16.5-inch octagonal prestressed
concrete pile driven to 60 m depth through coral clay and
sand. Modulus relations as obtained from uppermost gage
(1.5 m below head, i.e., 3.6b).
The tangent stiffness approach can be applied to all
gage levels. The differentiation eliminates influence
of past shear forces and residual load. Non-equal load
increment duration will adversely affect the results.
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39
Unlike steel, the modulus of concrete varies and depends on curing, proportioning,
mineral, etc. and it is strain dependent. However, the cross sectional area of steel in an
instrumented steel pile is sometimes not that well known.
y = -0.0013x + 46.791
200 300 400 500 600
STRAIN, με
30
35
40
45
50
55
60
0 100 200 300 400 500 600
STRAIN, με
TANGENTSTIFFNESS,EA(GN)
GN) = 46.5 from tangent stiffness
GN) = 46.8 - 0.001µε from secant stiffness
y = 0.000x + 46.451
TANGENT STIFFNESS, EA = ∆Q/∆εCANT STIFFNESS, EA = Q/ε
(Data from Bradshaw et al. 2012)
Pile stiffness for a 1.83 m diameter steel pile; open-toe pipe pile.
Strain-gage pair placed 1.8 m below the pile head.
y = -0.0013x + 46.791
30
35
40
45
50
55
60
0 100 200 300 400 500 600
STRAIN, με
SECANTSTIFFNESS,EA(GN)
30
35
40
45
50
55
60
0 100 200 300
STRAIN, με
TANGENTSTIFFNESS,EA(GN)
EAsecant (GN) = 46.5 from tangent stiffness
EAsecant (GN) = 46.8 - 0.001µε from secant stiffness
TANGENT STIFFNESSSECANT STIFFNESS, EA = Q/ε
40
Pile stiffness (Q/ε and ΔQ/Δε versus ε) for a 600 mm diameter concreted
pipe pile. The gage level was 1.6 m (3.2b) below the pile head
Data from Fellenius et al. 2003
100 150 200 250 300
STRAIN, µε
0
5
10
15
0 50 100 150 200 250 300
STRAIN, µε
TANGENTSTIFFNESS,EA(GN)
y = -0.003x + 7.41
y = -0.004x + 7.21
GN) = 7.2 - 0.002µε from tangent stiffness
GN) = 7.4 - 0.003µε from secant stiffness
TANGENT STIFFNESS, EA = ∆Q/∆εCANT STIFFNESS, EA = Q/ε
For "calibrating" uppermost gage level, the secant
method appears to be the better one to use, right?
0
5
10
15
0 50 100 150 200 250 300
STRAIN, µε
SECANTSTIFFNESS,EA(GN)
0
5
10
15
0 50 100 150
STRAIN, µ
TANGENTSTIFFNESS,EA(GN)
y = -0.003x + 7.41
EAsecant (GN) = 7.2 - 0.002µε from tangent stiffness
E Asecant (GN) = 7.4 - 0.003µε from secant stiffness
TANGENT STIFFNESSECANT STIFFNESS, EA = Q/ε
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41
y = -0.0053x + 11.231
0
10
20
30
40
50
0 100 200 300 400 500
STRAIN (µε)
SECANTSTIFFNESS,EA(GN)
y = -0.0055x + 9.995
0
10
20
30
40
50
0 100 200 300 400 500
STRAIN (µε)
TANGENTSTIFFNESS,EA(GN)
EAsecant (GN) = 10.0 - 0.003µε from tangent stiffness
E Asecant (GN) = 11.2 - 0.005µε from secant stiffness
Secant stiffness after adding
20µε to each strain value
Secant stiffness from
tangent stiffness
TANGENT STIFFNESS, EA = ∆Q/∆εSECANT STIFFNESS, EA = ∆Q/∆ε
Pile stiffness for a 600-mm diameter prestressed pile.
The gage level was 1.5 m (2.5b) below pile the head.
Data from CH2M Hill 1995
Or this case? Here, that initial "hyperbolic" trend can
be removed by adding a mere 20 µε to the strain data,
"correcting the zero" reading, it seems.
4242
But, is the “no-load” situation really the
reading taken at the beginning of the test?
What is the true “zero-reading” to use?
The strain-gage measurement is
supposed to be the change of strain due
to the applied load relative the “no-load”
situation (i.e., when no external load acts
at the gage location).
Determining load from strain-gage measurements in the pile
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4343
• We often assume – somewhat optimistically or
naively – that the reading before the start of the test
represents the “no-load” condition.
• However, at the time of the start of the loading test,
loads do exist in the pile and they are often large.
• For a grouted pipe pile or a concrete cylinder pile,
these loads are to a part the effect of the temperature
generated during the curing of the grout.
• Then, the re-consolidation (set-up) of the soil after the
driving or construction of the pile will impose additional
loads on the pile.
44
B. Load and resistance in DA
for the maximum test load
Example from Gregersen et al., 1973
0
2
4
6
8
10
12
14
16
18
0 50 100 150 200 250 300
LOAD (KN)
DEPTH(m)
Pile DA
Pile BC,
Tapered
0
2
4
6
8
10
12
14
16
18
0 100 200 300 400 500 600
LOAD (KN)
DEPTH(m)
True
Residual
True minus
Residual
0
2
4
6
8
10
12
14
16
18
0 50 100 150 200 250 300
LOAD (KN)
DEPTH(m)
Pile DA
Pile BC,
Tapered
0
2
4
6
8
10
12
14
16
18
0 100 200 300 400 500 600
LOAD (KN)
DEPTH(m)
True
Residual
True minus
Residual
A. Distribution of residual load in DA and BC
before start of the loading test
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45
Hysteresis loop for shaft resistance
mobilized in a static loading test
ABOVE THE NEUTRAL PLANE When no residual load
is present in the pile at the start of the test, the
starting point of the load-movement response is the
origin, O, and in a subsequent static loading test, the
shaft shear is mobilized along Path O-B. Residual load
develops as negative skin friction along Path D-A
(plotting from “D” instead of from “O”). Then, in a
static loading test, the shaft shear is mobilized along
Path A-O-B. However, if presence of residual load is
not recognized, the path will be thought to be along A-B
-- practically the same. If Point B represents fully
mobilized shaft resistance, then, the assumption of no
residual load in the pile will indicate a "false" resistance
that is twice as large as the "true" resistance.
SHAFTRESISTANCE
MOVEMENT
+
-
+rs
B
A
O
-rs
F
A
L
S
E
T
R
U
E
C
D
Above the neutral plane
SHAFTRESISTANCE
MOVEMENT
X
O
T
R
U
E
Y
Z
+
Belowthe neutral plane
F
A
L
S
E
Residual load affecting shaft resistance determined from a static loading test
BELOW THE NEUTRAL PLANE When no residual load
is present in the pile at the start of the test, the
starting point of the load-movement response is the
origin, O, and in a subsequent static loading test, the
shaft shear is mobilized along Path O-Z-X. Residual load
develops as positive shaft resistance along Path O-Z.
Then, in a static loading test, additional shaft resistance
is mobilized along Path Z-X. However, if presence of
residual load is not recognized, the origin will be thought
to be O, not Z. If Point X represents fully mobilized
shaft resistance, then, the assumption of no residual
load in the pile will indicate a "false" resistance that
could be only half the "true" resistance.
“Continuation” loop for shaft resistance
mobilized in a static loading test
46
Similar to the below the N.P. for the shaft, if residual load develops, it will be along Path O-Z. Then, in a
static loading test, the toe resistance (additional) is mobilized along Path Z-X and on to Y and beyond.
Pile toe response in unloading and reloading in a static loading test
When the pile construction has involved an unloading, say, at Point X, per the Path X-I-II, the reloading in the
static loading test will be along Path I-II-X and on to Y. Unloading of toe load can occur for driven piles and
jacked-in piles, but is not usually expected to occur for bored piles (drilled shafts). However, it has been
observed in such piles, in particular for test piles which have had additional piles constructed around them
and for full displacement piles. The toe resistance be underestimated and the break in the reloading curve at
Point X can easily be mistaken for a failure load and be so stated.
SHAFTRESISTANCE
MOVEMENT
X
O
T
R
U
E
Y
Z
+
Belowthe neutral plane
F
A
L
S
E
TOERESISTANCE
MOVEMENT
O
T
R
U
E
RESIDUAL
TOE LOAD
F
A
L
S
E
X
II
Y
Z
F
A
L
S
E III
I
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47
Method for evaluating
the residual load distribution
0
2
4
6
8
10
12
14
16
0 500 1,000 1,500 2,000
RESISTANCE (KN)
DEPTH(m)
Measured Shaft
Resistance
Divided by 2
Residual
Load
Measured
Load
True
Resistance
Extrapolated
True Resistance
Shaft
Resistance
4848
Immediately
before the test, all
gages must be
checked and "Zero
Readings" must be
taken.
Answer to the question
in the graph:
No, there's always
residual load in a
test pile.
0
5
10
15
20
25
30
35
40
45
50
55
60
-300 -200 -100 0 100 200 300 400
DEPTH(m)
STRAIN (µε)
Shinho Pile
Zero Readings.
Does it mean
zero loads?
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4949
Gages were read
after they had been
installed in the pile
( = “zero” condition)
and then 9 days
later (= green line)
after the pile had
been concreted and
most of the
hydration effect
had developed.
0
5
10
15
20
25
30
35
40
45
50
55
60
-300 -200 -100 0 100 200 300 400
DEPTH(m)
STRAIN (µε)
"Zero"
condition
Before
grouting
9 days later
after installing
gages (main
hydraution has
developed)
Change
(tension)
5050
Strains measured
during the following
additional 209-day
wait-period.
0
5
10
15
20
25
30
35
40
45
50
55
60
-300 -200 -100 0 100 200 300 400
STRAIN (µε)
DEPTH(m)
9d
15d
23d
30d
39d
49d
59d
82d
99d
122d
218d
Day of
Test
At an E- modulus of 30 GPa,
this strain change corresponds
to a load change of 3,200 KN
26. 4/18/2015
26
5151
Concrete hydration temperature measured in a grouted
concrete cylinder pile
0
10
20
30
40
50
60
70
0 24 48 72 96 120 144 168 192 216 240
HOURS AFTER GROUTING
TEMPERATURE(°C)
Temperature at various
depths in the grout of a 0.4 m
center hole in a 56 m long,
0.6 m diameter, cylinder pile.
Pusan Case
5252
-400
-300
-200
-100
0
100
0 5 10 15 20 25 30 35
DAY AFTER GROUTING
CHANGEOFSTRAIN(µε)
Rebar Shortening
Slight Recovery of Shortening
Change of strain measured in a 74.5 m
long, 2.6 m diameter bored pile
Change of strain during the hydration of the grout in the Golden Ears Bridge test pile
27. 4/18/2015
27
5353
0
10
20
30
40
50
60
70
80
90
100
0 40 80 120 160 200 240
Time (h)
TEMPTATURE(ºC)
S
W
N
E
April 25,
2006
Temperature During Curing of a 2m Lab Specimen
5454
Strain History During Curing of a 2 m Long Full-width Lab Specimen
First 5 days after placing concrete
Pusan Case
-300
-250
-200
-150
-100
-50
0
50
0 1 2 3 4 5
Days after Grouting
CHANGEOFSTRAIN(µε)
PHC Piece
RECOVERY OF SHORTENING (LENGTHENING)INCREASING
SHORTENING
OF REBAR
A
IncreasingForceintherebar
COMPRESSION
28. 4/18/2015
28
5555
-200
-150
-100
-50
0
50
100
0 100 200 300 400 500
Time (days)
STRAIN(µε)
S
N
E
W
Pile piece
submerged
INCREASING TENSION
Concrete Cylinder Piece
Strain History during 400+ days including
letting it swell from absorption of water
IncreasingForceintherebar
5656
The strain gages themselves are not are
temperature sensitive, but the records may be!
The vibrating wire and the rebar have almost the same temperature
coefficient. However, the coefficients of steel and concrete are slightly
different. This will influence the strains during the cooling of the grout.
More important, the rise of temperature in the grout could affect the zero
reading of the wire and its strain calibration. It is necessary to “heat-cycle”
(anneal) the gage before calibration. (Not done by all, but annealing is a
routine measure of Geokon, US manufacturer of vibrating wire gages).
29. 4/18/2015
29
5757
• Readings should be taken immediately before
(and after) every event of the piling work and not
just during the actual loading test
• The No-Load Readings will tell what happened to
the gage before the start of the test and will be
helpful in assessing the possibility of a shift in the
reading value representing the no-load condition
• If the importance of the No-Load Readings is
recognized, and if those readings are reviewed
and evaluated, then, we are ready to consider
the actual readings during the test
5858
Good measurements do not guarantee good conclusions!
A good deal of good thinking is necessary, too
Results of static loading tests on a 40 m long, jacked-in,
instrumented steel pile in a saprolite soil
0
5
10
15
20
25
30
35
40
45
0 2,000 4,000 6,000 8,000 10,000
LOAD (KN)
DEPTH(m)
0
5
10
15
20
25
30
35
40
0 50 100 150 200 250
UNIT SHAFT SHEAR (KPa)
DEPTH(m)
?
30. 4/18/2015
30
59
0
5
10
15
20
25
30
35
40
45
0 2,000 4,000 6,000 8,000 10,000
LOAD (KN)
DEPTH(m)
ß = 0.3
ß = 0.4
A more thoughtful analysis of the data
0
5
10
15
20
25
30
35
40
45
0 50 100 150 200 250
UNIT SHAFT SHEAR (KPa)
DEPTH(m)
ß = 0.3
ß = 0.4
The butler The differentiation did it
60
0
500
1,000
1,500
2,000
0 10 20 30 40 50
LOADatPILEHEAD(kN)
PILE HEAD MOVEMENT (mm)
HEADTOE
300 mm diameter,30 m long concrete pile
E = 35 GPa;ß = 0.30; Strain-softening
SHORTENING
0
500
1,000
1,500
2,000
0 10 20 30 40 50
LOAD(kN)
MOVEMENT (mm)
HEAD
SHAFTTOE
300 mm diameter,30 m long concrete pile
E = 35 GPa; ß = 0.30 at δ = 5 mm;
Strain-softening: Zhang with δ = 5 mm and a = 0.0125
SHORTENING
HEAD
TOE
t-z curve (shaft)
Zhang function
with δ = 5 mm and a = 0.0125
0
250
500
750
1,000
0 5 10 15 20 25 30
SEGMENT MOVEMENT AT MID-POINT (mm)
SEGMENTSHAFTRESSISTANCEATMID-POINT(kN)
lower
middle
upper
0 5 10 15 20 25 30
0 5 10 15 20 25 30
0 5 10 15 20 25 30
0 5 10 15 20 25 30
TOE
HEAD
TOE
MOVEMENT
A static loading test with a toe
telltale to measure toe
movement—typical records
Now with instrumentation to
separate shaft and toe
resistances
Shaft resistance load-movement
curve (t-z function) —typical
31. 4/18/2015
31
61
0
5
10
15
20
25
30
35
40
0 500 1,000 1,500 2,000 2,500 3,000
DEPTH(m)
LOAD (kN)
FILL
ß= 0.30
SOFTCLAY
ß= 0.20
SILT
ß= 0.25
SAND
ß= 0.45
rt = 3 MPa
Profile
FILL with ß = 0.30
Ratio function
with δ = 5 mm and θ = 0.15
Shaft
CLAY with ß = 0.20
Hansen 80-% function
with δ = 5 mm and C1 = 0.0022
Shaft
SILT with ß = 0.20
Exponentional function
with b = 0.40
Shaft
SAND with ß = 0.45
Ratio function
with δ = 5 mm and θ = 0.20
Shaft
SAND with rt = 2 MPa
Ratio function
with at δ = 5 mm and θ = 0.50
Toe
400 mm diameter, 38 m long, phictitious concrete pile
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
0 10 20 30 40 50 60 70
LOAD(kN)
MOVEMENT (mm)
Head-down static loading testload-movements
Head
Shaft
Toe
Compression
The simulations are made using UniPile Version 5
62
Arcos Egenharia
E-cellpile
at
Rio Negro Ponte
Manaus – Iranduba
Brazil
The bi-directional test
Arcos Egenharia de Solos
Bidirectional test at
Rio Negro Ponte
Manaus—Iranduba, Brazil
32. 4/18/2015
32
6363
The difficulty associated with wanting to know the pile-toe load-movement response,
but only knowing the pile-head load-movement response, is overcome in the
bidirectional test, which incorporates one or more sacrificial hydraulic jacks placed at or
near the toe (base) of the pile to be tested (be it a driven pile, augercast pile, drilled-
shaft pile, precast pile, pipe pile, H-pile, or a barrette). Early bidirectional testing was
performed by Gibson and Devenny (1973), Horvath et al. (1983), and Amir (1983). About
the same time, an independent development took place in Brazil (Elisio 1983; 1986),
which led to an industrial production offered commercially by Arcos Egenharia de Solos
Ltda., Brazil, to the piling industry. In the 1980s, Dr. Jorj Osterberg also saw the need for
and use of a test employing a hydraulic jack arrangement placed at or near the pile toe
(Osterberg 1989) and established a US corporation called Loadtest Inc. to pursue the bi-
directional technique. On Dr. Osterberg's in 1988 learning about the existence and
availability of the Brazilian device, initially, the US and Brazilian companies collaborated.
Somewhat unmerited, outside Brazil, the bidirectional test is now called the “Osterberg
Cell test” or the “O-cell test” (Osterberg 1998). During the about 30 years of commercial
application, Loadtest Inc. has developed a practice of strain-gage instrumentation in
conjunction with the bidirectional test, which has vastly contributed to the knowledge
and state-of-the-art of pile response to load.
The bi-directional test
6464
Schematics of the bidirectional test
(Meyer and Schade 1995)
-10
-8
-6
-4
-2
0
2
4
6
8
10
0 10 20 30 40 50 60 70 80
MOVEMENT(mm)
LOAD (tonne)
Test at
BancoEuropeu
Elisio (1983)
Pile PC-1
June 3, 1981
Upward
Downward
11.0m2.0m
E
520 mm
Upward Load
THE CELL
Telltales
and
Grout Pipe
Pile Head
Downward Load
Typical Test Results
(Data from Eliso 1983)
34. 4/18/2015
34
6767
The bidirectional cell can also be installed in a driven pile (after the
driving). Here in a 600 mm cylinder pile with a 400 mm central void.
68Bidirectional cell attached to an H-beam inserted in a augercast pile
after grouting.
36. 4/18/2015
36
7171
Test on a 1,250
mm diameter,
40 m long,
bored pile at
US82 Bridge
across
Mississippi
River
installed into
dense sand
-80
-60
-40
-20
0
20
40
60
80
100
120
0 2,000 4,000 6,000 8,000 10,000
LOAD (KN)
MOVEMENT(mm)
UPPER PLATE
UPWARD MVMNT
LOWER PLATE
DOWNWARD MVMNT
Weight
of
Shaft
Residual
Load
Shaft
Toe
Project by Loadtest Inc., Gainesville, Florida
7272
The Equivalent Head-down Load-movement Curve
Measured upward and downward curves
With correction for the increased pile
compression in the head-down test
Construction of the “Direct Equivalent Curve”
Reference: Appendix to regular reports by Fugro Loadtest Inc.
37. 4/18/2015
37
7373
From the upward and downward results, one can produce
the equivalent head-down load-movement curve that one
would have obtained in a routine “Head-Down Test”
“Head –down”
cnt.
74
Upward and downward curves fitted to measured curves
UniPile5 analysis using the t-z and q-z curves fitted to the load-movement
curves at the gage levels in an effective-stress simulation of the test
-10
0
10
20
30
40
0 500 1,000 1,500 2,000
LOAD (kN)
MOVEMENT(mm)
Upward
Downward
TEST
DATA FITTED
TO TEST
DATA
Example 1 Example 2
-80
-60
-40
-20
0
20
40
60
80
100
120
0 2,000 4,000 6,000 8,000 10,000
MOVEMENT(mm)
LOAD (kN)
UPWARD
DOWNWARD
Weightof
Shaft
Residual
Load
Simulated
curve
Simulated
curve
38. 4/18/2015
38
75
0
200
400
600
800
1,000
1,200
1,400
1,600
1,800
0 5 10 15 20 25 30 35 40 45
MOVEMENT (mm)
LOAD(KN)
Fitted to the
upward curve
Calculated as "true"
head-down response
using the t-z functions
fitted to the test data
Measured
upward
curve
Example 2: The upward shaft response extracted and compared
to the response of the shaft to an "Equivalent Head-down Test
The difference shown above between the upward BD cell-plate and the
head-down load-movement curves is due to the fact that the upward cell
engages the lower soil first, whereas the head-down test engages the
upper soils first, which are less stiff than the lower soils.
Example 1 Example 2
0
2,000
4,000
6,000
8,000
10,000
0 25 50 75 100 125
LOAD(kN)
MOVEMENT (mm)
Measured
Upward
( )
Upward Test
Measured and
simulated
As in a
Head-down
Test
Head-down combining
upward and downward
curves
Head-down combining
upward and downward
curves
76
The effect of residual load on a bidirectional test
The cell load includes the residual load whereas the
load evaluated from the strain-gages does not.
0
5
10
15
20
25
30
35
0 500 1,000 1,500 2,000 2,500 3,000 3,500
LOAD (KN)
DEPTH(m)
O-CELL
AND PARTIAL
RESIDUAL LOAD
Residual
Load
False
Resistance
True
Resistance
True Shaft
Resistance
Equivalent
Head-down
False Resistance
The O-cellThe Cell
39. 4/18/2015
39
77
Similar to combining a compression test with a tension test.
combining a bidirectional test and a head-down compression
test will help in determining the true resistance
0
5
10
15
20
25
30
35
0 500 1,000 1,500 2,000 2,500 3,000 3,500
LOAD (KN)
DEPTH(m)
HEAD-DOWN
AND PARTIAL
RESIDUAL LOAD
Residual
Load
True
Resistance
False
Head-down
Residual and True
Toe Resistance
Transition
Zone
True Shaft
Resistance
False
Tension
Test
Not directly
useful below
this level
78
-15
-10
-5
0
5
10
15
20
25
0 100 200 300 400 500 600 700 800 900 1,000
MOVEMENT(mm)
LOAD (kN)
E
8.5
3.0
If unloadedafter10 min
ß = 0.4 to 2.5 m δ = 5 mm ϴ = 0.24
ß = 0.6 to 6.0 m δ = 5 mm ϴ = 0.24
ß = 0.9 to cell δ = 5 mm ϴ = 0.24
ß = 0.9 to toe δ = 5 mm ϴ = 0.30
rt = 3,000 kPa δ = 30 mm ϴ = 0.90
PCE-02
-30
-25
-20
-15
-10
-5
0
5
10
15
0 100 200 300 400 500 600 700 800 900 1,000
MOVEMENT(mm)
LOAD (kN)PCE-07
E
7.2
4.3
ß = 0.5 to 2.5 m δ = 5 mm ϴ = 0.30
ß = 0.7 to 6.0 m δ = 5 mm ϴ = 0.30
ß = 0.8 to cell δ = 5 mm ϴ = 0.30
ß = 0.6 to toe δ = 5 mm C1 = 0.0063
rt = 100 kPa δ = 30 mm C1 = 0.0070
A CASE HISTORY Bidirectional tests performed at a site in Brazil on two Omega Piles
(Drilled Displacement Piles, DDP, also called Full Displacement Piles, FDP) both with
700 mm diameter and embedment 11.5 m. Pile PCE-02 was provided with a
bidirectional cell level at 7.3 m depth and Pile PCE-07 at 8.5 m depth.
Acknowledgment: The bidirectional test are courtesy of
Arcos Egenharia de Solos Ltda., Belo Horizonte, Brazil.
40. 4/18/2015
40
79
0
500
1,000
1,500
2,000
2,500
3,000
0 5 10 15 20 25 30
LOAD(kN)
MOVEMENT (mm)
PCE-02
PCE-07
Max downward
movement
Max upward
movement
Max upward
movement
Max downward
movement
Pile PCE-02
Compression
PCE-02, Toe
PCE-07, Toe
PCE-02 and -07
Shaft
0
2
4
6
8
10
12
0 400 800 1,200 1,600
DEPTH(m)
LOAD (kN)
PCE-07
PCE-02
0
5
10
15
20
25
30
0 400 800 1,200 1,600
MOVEMENT(mm)
TOE LOAD (kN)
PCE-02
PCE-07
A
B
Equivalent Head-down
Load-movements
Equivalent Head-down
Load-distributions
After data reduction and processing
A conventional head-down test would not
have provided the reason for the lower
“capacity” of Pile PCE-02
8080
Pensacola, Florida
410 mm diameter, 22 m
long, precast concrete pile
driven into silty sand
41. 4/18/2015
41
8181
Pensacola, Florida, USA
-4
-3
-2
-1
0
1
2
3
4
0 500 1,000 1,500 2,000 2,500
LOAD (KN)
MOVEMENT(mm)
-10
0
10
20
30
40
50
60
0 500 1,000 1,500 2,000 2,500
LOAD (KN)
MOVEMENT(mm)
Bidirectional-cell test on a 16-inch,
72-ft, prestressed pile driven into
sand.
Cell
After the push test,
the pile toe is located
higher up than when
the test started!
cnt.
Data courtesy of Loadtest Inc.
82
Los Angeles Coliseum, 1994
The Northridge earthquake in Los Angeles, California,
in January 1994 was a "strong" moment magnitude
of 6.7 with one of the highest ground acceleration
ever recorded in an urban area in North America.
The piles had been designed using the usual design approach
with adequate factors of safety to guard against the unknowns.
Moreover, the acceptable maximum movement was more
stringent than usual.
The earthquake caused an estimated $20 billion in
property damage. Amongst the severely damaged
buildings was the Los Angeles Memorial Coliseum,
which repairs and reconstruction cost about $93
million. The remediation work included construction
of twenty-eight, 1,300 mm diameter, about 30 m long,
bored piles, each with a working load of almost
9,000 KN (2,000 kips), founded in a sand and gravel
deposit.
It was imperative that all construction work was finished in six
months (September 1994, the start of the football season).
However, after constructing the first two piles, which took six
weeks, it became obvious that constructing the remaining
twenty-six piles would take much longer than six months.
Drilling deeper than 20 m was particularly time-consuming. The
design was therefore changed to about 18 m length, combined
with equipping every pile with a bidirectional cell at the pile toe.
Note, the cell was now used as a construction tool.
42. 4/18/2015
42
83
Los Angeles Coliseum, 1994
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10
20
30
40
0 2,000 4,000 6,000 8,000 10,000
LOAD (KN)
MOVEMENT(mm)
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10
20
30
40
0 2,000 4,000 6,000 8,000 10,000
LOAD (KN)
MOVEMENT(mm)
Schmertmann (2009, 2012), Fellenius (2011)
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10
20
30
40
0 2,000 4,000 6,000 8,000 10,000
LOAD (KN)
MOVEMENT(mm)
THE BIDIRECTIONAL-CELL AS A
CONSTRUCTION TOOL
TESTS ON EVERY PILE
ONE OF THE PILES
THREE OF THE PILES
ALL PILES
cnt.
84
FIRST STAGE LOADING; "VIRGIN" TESTS
WITH LINE SHOWING AVERAGE SLOPE
RELOADING STAGE. DOWNWARD DATA ONLY
The first stage loading is of interest in the context of general evaluation of
test results and applying them to design. The second is where the
bidirectional cell was used as a preloading tool, resulting in a significant
increase of toe stiffness, much in the way of the Expander base.
0
2,000
4,000
6,000
8,000
10,000
0 25 50 75 100 125 150
MOVEMENT (mm)
LOAD(KN)
Downward, First Loading
A
0
2,000
4,000
6,000
8,000
10,000
0 25 50 75 100 125 150
MOVEMENT (mm)
LOAD(KN)
Downward, Second Loading
B
cnt.
43. 4/18/2015
43
85
0 2,000 4,000 6,000 8,000
RealtiveFrequency
Mean
2σ
4σ
σ = 1,695
µ = 3 , 7 3 1
NORMAL DISTRIBUTION of TOE LOAD AT 25 mm
0
RealtiveFrequency
Mean = 71
MPa
2σ
4σ
σ = 26
µ = 7 1
NORMAL DISTRIBUTION OF STIFFNESS BETWEEN 25 mm AND 50 mm
STIFFNESS (MPa)
Variation of toe load for 25 mm movement
Slope of load-movement curve (i.e., stiffness)
E = 70 MPa = 10 ksi
= 1.4 ksf
m = 700 (j=1)
0
3,000
6,000
9,000
20 30 40 50 60
MOVEMENT (mm)
LOAD(KN)
cnt.
8686
Bidirectional Tests
on a 1.4 m diameter
bored pile in North-
West Calgary
constructed in silty
glacial clay till
A study of Toe and Shaft Resistance
Response to Loading and correlation to CPTU
calculation of capacity
44. 4/18/2015
44
8787
0
5
10
15
20
25
30
0 10 20 30
Cone Stress, qt (MPa)
DEPTH(m) 0
5
10
15
20
25
30
0 200 400 600 800
1,00
0
Sleeve Friction, fs (KPa)
DEPTH(m)
0
5
10
15
20
25
30
-10
0 0 100 200 300 400 500
Pore Pressure (KPa)
DEPTH(m)
0
5
10
15
20
25
30
0 1 2 3 4 5
Friction Ratio, fR (%)
DEPTH(m)
PROFILE
The upper 8 m
will be removed
for basement
uneutral
14 m
net pile
length
GW
Cone Penetration Test with Location of Test Pile
cnt.
88
Pile Profile and Cell Location Cell Load-movement Up and Down
cnt.
-30
-20
-10
0
10
20
30
40
50
60
70
80
0 1,000 2,000 3,000 4,000 5,000 6,000
MOVEMENT(mm)
LOAD (kN)
ELEV.(m)
#5
#4
#3
#2
#1
Pile Toe Elevation
46. 4/18/2015
46
Analysis of the results
of a bidirectional test on
a 21 m long bored pile
A bidirectional test was performed on a 500-mm diameter, 21 m
long, bored pile constructed through compact to dense sand by
driving a steel-pipe to full depth, cleaning out the pipe, while
keeping the pipe filled with betonite slurry, withdrawing the pipe,
and, finally, tremie-replacing the slurry with concrete. The
bidirectional cell (BDC) was attached to the reinforcing cage
inserted into the fresh concrete. The BDC was placed at 15 m
depth below the ground surface.
The pile will be one a group of 16 piles (4 rows by 4 columns)
installed at a 4-diameter center-to-center distance. Each pile is
assigned a working load of 1,000 kN.
compact
SAND
CLAY
compact
SAND
dense
SAND
The sand becomes very
dense at about 35 m depth
91
0
5
10
15
20
25
0 5 10 15 20 25
DEPTH(m)
Cone Stress, qt (MPa)
0
5
10
15
20
25
0 20 40 60 80 100
DEPTH(m)
Sleeve Friction, fs (kPa)
0
5
10
15
20
25
0 50 100 150 200 250
DEPTH(m)
Pore Pressure (kPa)
0
5
10
15
20
25
0.0 0.5 1.0 1.5 2.0
DEPTH(m)
Friction Ratio, fR (%)
0
5
10
15
20
25
0 10 20 30 40 50
DEPTH(m)
N (blows/0.3m)
compact
SAND
CLAY
compact
SAND
dense
SAND
The soil profile determined by CPTU and SPT
92
0
5
10
15
20
25
0 5 10 15 20 25
DEPTH(m)
Cone Stress, qt (MPa)
0
5
10
15
20
25
0 20 40 60 80 100
DEPTH(m)
Sleeve Friction, fs (kPa)
0
5
10
15
20
25
0 50 100 150 200 250
DEPTH(m)
Pore Pressure (kPa)
0
5
10
15
20
25
0.0 0.5 1.0 1.5 2.0
DEPTH(m)
Friction Ratio, fR (%)
0
5
10
15
20
25
0 10 20 30 40 50
DEPTH(m)
N (blows/0.3m)
compact
SAND
CLAY
compact
SAND
dense
SAND
47. 4/18/2015
47
The results of the bidirectional test
93
-50
-40
-30
-20
-10
0
10
20
30
40
50
0 200 400 600 800 1000 1200
MOVEMENT(mm)
LOAD (kN)
Pile Head
UPWARD
BDC DOWNWARD
15.0m6.0m
Acknowledgment: The bidirectional test data are courtesy
of Arcos Egenharia de Solos Ltda., Belo Horizonte, Brazil.
To fit a simulation of the test to the results, first input is the effective stress parameter (ß)
that returns the maximum measured upward load (840 kN), which was measured at the
maximum upward movement (35 mm). Then, “promising” t-z curves are tried until one is
obtained that, for a specific coefficient returns a fit to the measured upward curve. Then,
for the downward fit, t-z and q-z curves have to be tried until a fit of the downward load
(840 kN) and the downward movement (40 mm) is obtained.
Usually for large movements,
as in the example case, the
t-z functions show a elastic-
plastic response. However,
for the example case , no
such assumption fitted the
results. In fact, the best fit
was obtained with the Ratio
Function for the entire length
of the pile shaft.
94
t-z and q-z Functions
SAND ABOVE BDC
Ratio function
Exponent: θ = 0.55
δult = 35 mm
SAND BELOW BDC
Ratio function
Exponent: θ = 0.25
δult = 40 mm
TOE RESPONSE
Ratio function
Exponent: θ = 0.40
δult = 40 mm
CLAY (Typical only,
not used in the
simulation)
Exponential function
Exponent: b = 0.70
48. 4/18/2015
48
The final fit of simulated curves to the measured
95
-50
-40
-30
-20
-10
0
10
20
30
40
50
0 200 400 600 800 1,000 1,200
MOVEMENT(mm)
LOAD (kN)
Pile Head
UPWARD
BDC
DOWNWARD
15.0m6.0m
0
5
10
15
20
25
0 200 400 600 800 1,000
DEPTH(m)
LOAD (kN)
BDC load
0
5
10
15
20
25
0 10 20 30 40 50
DEPTH(m)
N (blows/0.3m)
compact
SAND
CLAY
compact
SAND
dense
SAND
With water
force
Less
buoyant
weight
UPWARD
DOWNWARD
The test pile was not instrumented. Had it been, the load distribution of the bidirectional
test as determined from the gage records, would have served to further detail the
evaluation results. Note the below adjustment of the BDC load for the buoyant weight
(upward) of the pile and the added water force (downward).
The analysis results appear to
suggest that the pile is affected
by a filter cake along the shaft
and probably also a reduced
toe resistance due to debris
having collected at the pile toe
between final cleaning and the
placing of the concrete.
96
49. 4/18/2015
49
The final fit establishes the soil response and allows the
equivalent head-down loading- test to be calculated
0
500
1,000
1,500
2,000
2,500
0 5 10 15 20 25 30 35 40 45 50
LOAD(kN)
MOVEMENT (mm)
Equivalent
Head-Down test
HEAD
TOE
Pile head movement for
30 mm pile toe
movement
Pile head movement for
5 mm pile toe movement
97
When there is no obvious point on the
pile-head load-movement curve, the
“capacity” of the pile has to be
determined by one definition or other—
there are dozens of such around. The
first author prefers to define it as the
pile-head load that resulted in a 30-mm
pile toe movement. As to what safe
working load to assign to a test, it often
fits quite well to the pile head load that
resulted in a 5-mm toe movement.
The most important aspect for a safe
design is not the “capacity” found from
the test data, but what the settlement of
the structure supported by the pile(s)
might be. How to calculate the
settlement of a piled foundation is
addressed a few slides down.
The final fit establishes also the equivalent head-down distributions of shaft
resistance and equivalent head-down load distribution for the maximum load
(and of any load in-between, for that matter). Load distributions have also been
calculated from the SPT-indices using the Decourt, Meyerhof, and O’Neil-Reese
methods, as well that from the Eslami-Fellenius CPTU-method.
98
0
5
10
15
20
25
0 500 1,000 1,500 2,000
DEPTH(m)
LOAD (kN)
SPT-Meyerhof
Test
0
5
10
15
20
25
0 10 20 30 40 50
DEPTH(m)
N (blows/0.3m)
compact
SAND
CLAY
compact
SAND
dense
SAND
SPT-Decourt
SPT-Decourt
SPT-O'Neill
Test
CPTU-E-F
By fitting a UniPile simulation to the
measured curves, we can determine all
pertinent soil parameters, the applicable t-z
and q-z functions, and the distribution of
the equivalent head-down load-distribution.
The results also enable making a
comparison of the measured pile response
to that calculated from the in-situ test
methods.
However, capacity of the single pile is just
one aspect of a piled foundation design.
As mentioned, the key aspect is the
foundation settlement.
Note, the analysis results suggest that the
pile was more than usually affected by
presence of a filter cake along the pile
shaft and by some debris being present at
the bottom of the shaft when the
concrete was placed in the hole. An
additional benefit of a UniPile analysis.
