bengt h. fellenius the static loading test 2nd cfpb... · bengt h. fellenius the static loading...
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Bengt H. Fellenius
The Static Loading Test
Performance, Instrumentation, Interpretation
First K.R. Massarsch Lecture
Fellenius, B.H., 2015. The Static Loading Test. Segundo Congreso Internacional de Fundaciones Profundas de Bolivia, First K.R. Massarsch Lecture, Santa Cruz May 12-15, 62 p
2
A routine static loading test provides the load-movement of the pile head...
and the pile capacity?
3
The Offset Limit Method Davisson (1972)
OFFSET (inches) = 0.15 + b/120
OFFSET (mm) = 4 + b/120
b = pile diameter
LL
EAQ
Q
LTom 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 5000
500,000
1,000,000
1,500,000
2,000,000
LOAD (kips)
LOAD
/MVM
NT
-- Q
/s (
inch
/kip
s)
Ult.Res = 474 kips
Linear Regression Line
0.0 0.5 1.0 1.5 2.00
100
200
300
400
500
MOVEMENT (inches)
LOAD
(ki
ps)
Q
1
2
C
CQu
C1 = Slope
C2 = Y-intercept
Q
Ru = 470 kips – 230 tons
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)
Load 10 % of pile head diameter
6
CHIN and DECOURT 235
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
LO
AD
(kN
)
MOVEMENT (mm)
OFFSET LIMIT LOAD 2,000 kN
Shaft
Head
Toe
CompressionLOAD = 3,100 kN for 30 mm toe movement
8
What really do we learn from unloading/reloading and what does unloading/reloading do to the gage records?
9
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)
LO
AD
(M
N)
Acceptance Criterion
0
5
10
15
20
25
30
0 25 50 75 100 125 150 175 200
MOVEMENT (mm)
LO
AD
(M
N)
Acceptance CriterionRepeat test
10
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)
LOA
D (
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)
"PE
RC
EN
T"
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
12
0
200
400
600
800
1,000
0 1 2 3 4 5 6 7
MOVEMENT (mm)
LOA
D (K
N) 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” pile is 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)
LOA
D (K
N) 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
13
0
200
400
600
800
0 2 4 6 8 10
PILE HEAD MOVEMENT (mm)
LOA
D P
ER
PIL
E (
KN
) Single PileAverage 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
14
Instrumentation
and
Interpretation
15
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?
16
Load distribution for constant unit shaft resistance Unit shaft resistance (constant with depth)
17
Linearly increasing unit shaft resistance and its load distribution
DE
PT
HLOAD IN THE PILE
DE
PT
H
SHAFT RESISTANCE
DE
PT
H
UNIT RESISTANCE
x = h/√2
h/2
A1
A2
x = h/√2
h
ah
ah2/2
ah2/200
00 "0"
ah
TELLTALE 0 Shaft Resistance
Resistance at TTL FootTelltale Foot
Linearly increasing unit shaft resistance 2
5.02
22 ahax
2
hx ===> 21 AA ===>
x
18
Hanifah, A.A. and Lee S.K. (2006)
Glostrext Retrievable Extensometer (Geokon 1300 & A9)
Anchor arrangement display Anchors installed
Geokon borehole extensometer
19
Gage for measuring displacement, i.e., distance change between upper and lower extensometers. Accuracy is about 0.02mm/5m corresponding to about 5 µε.
20
21
Rebar Strain Meter — “Sister Bar”
Reinforcing Rebar
Rebar Strain Meter
Wire Tie
Instrument Cable
or Strand
Wire Tie
Tied to Reinforcing Rebar Tied to Reinforcing Rings
Reinforcing Rebaror Strand
(2 places)
Rebar Strain Meter
Instrument Cables
(3 places, 120° apart)
Hayes 2002
Three bars?!
Reinforcing Rebar
Rebar Strain Meter
Wire Tie
Instrument Cable
or Strand
Wire Tie
Tied to Reinforcing Rebar Tied to Reinforcing Rings
Reinforcing Rebaror Strand
(2 places)
Rebar Strain Meter
Instrument Cables
(3 places, 120° apart)
22
0
2
4
6
8
10
12
14
16
18
20
0 50 100 150 200STRAIN (µε)
LO
AD
(M
N)
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)
LO
AD
(M
N)
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
23
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)
LO
AD
(M
N)
A&C+D
Means: A&C, B&D, AND A&B&C&D
A&C+BD 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.
24
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
25
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
ccsscomb AA
AEAEE
Ecomb = combined modulus Es = modulus for steel As = area of steel Ec = modulus for concrete Ac = area of concrete
26
• 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
27
0 200 400 600 8000
10
20
30
40
50
60
70
80
90
100
MICROSTRAIN
TAN
GE
NT
MO
DU
LUS
(G
Pa)
Level 1
Level 2
Level 3
Level 4
Level 5
Best Fit Line
Example of “Tangent Modulus Plot”
28
bad
dEt
ba
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
29
0 200 400 600 8000
10
20
30
40
50
60
70
80
90
100
MICROSTRAIN
TAN
GE
NT
MO
DU
LUS
(G
Pa)
Level 1
Level 2
Level 3
Level 4
Level 5
Best Fit Line
Example of “Tangent Modulus Plot”
Intercept is
”b”
Slope is “a”
30
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)
TA
NG
EN
T S
TIF
FN
ES
S,
∆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)
SE
CA
NT
S
TIF
FN
ES
S, Q
/ε (
GN
)
Secant DataSecant from Tangent DataTrend 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.
31
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
30
35
40
45
50
55
60
0 100 200 300 400 500 600
STRAIN, με
SE
CA
NT
ST
IFF
NE
SS
, EA
(G
N)
30
35
40
45
50
55
60
0 100 200 300 400 500 600
STRAIN, με
TA
NG
EN
T S
TIF
FN
ES
S, E
A (
GN
)
EAsecant (GN) = 46.5 from tangent stiffness
EAsecant (GN) = 46.8 - 0.001µε from secant stiffness
y = 0.000x + 46.451
TANGENT STIFFNESS, EA = ∆Q/∆εSECANT 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
SE
CA
NT
ST
IFF
NE
SS
, EA
(G
N)
30
35
40
45
50
55
60
0 100 200 300 400 500 600
STRAIN, με
TA
NG
EN
T S
TIF
FN
ES
S, E
A (
GN
)
EAsecant (GN) = 46.5 from tangent stiffness
EAsecant (GN) = 46.8 - 0.001µε from secant stiffness
y = 0.000x + 46.451
TANGENT STIFFNESS, EA = ∆Q/∆εSECANT STIFFNESS, EA = Q/ε
32
y = -0.0053x + 11.231
0
10
20
30
40
50
0 100 200 300 400 500
STRAIN (µε)
SE
CA
NT
ST
IFF
NE
SS
, EA
(G
N)
y = -0.0055x + 9.9950
10
20
30
40
50
0 100 200 300 400 500
STRAIN (µε)
TA
NG
EN
T S
TIF
FN
ES
S, E
A (
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
The initial "hyperbolic" trend can here be removed by adding a mere 20 µε to the strain data, "correcting the zero" reading, it seems.
33 33
• 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.
34
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)D
EP
TH
(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)
DE
PT
H (
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)
DE
PT
H (
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)
DE
PT
H (
m) True
Residual
True minus Residual
A. Distribution of residual load in DA and BC
before start of the loading test
35 35
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
DE
PT
H (
m)
STRAIN (µε)
Shinho Pile
Zero Readings. Does it mean zero loads?
36 36
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
DE
PT
H (
m)
STRAIN (µε)
"Zero" conditionBefore grouting
9 days laterafter installing gages (main hydraution has developed)
Change(tension)
37 37
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)
DE
PTH
(m
)
9d
15d
23d
30d
39d
49d
59d
82d
99d
122d
218d Day ofTest
At an E- modulus of 30 GPa, this strain change corresponds to a load change of 3,200 KN
38 38
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
TEM
PE
RA
TUR
E (
°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
39 39
-400
-300
-200
-100
0
100
0 5 10 15 20 25 30 35
DAY AFTER GROUTING
CH
AN
GE
OF
ST
RA
IN (µ
ε)
Rebar ShorteningSlight 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
40 40
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)
DE
PTH
(m
)
0
5
10
15
20
25
30
35
40
0 50 100 150 200 250
UNIT SHAFT SHEAR (KPa)
DE
PTH
(m
)
?
41
0
5
10
15
20
25
30
35
40
45
0 2,000 4,000 6,000 8,000 10,000
LOAD (KN)
DE
PTH
(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)
DE
PTH
(m
)
ß = 0.3
ß = 0.4
From UniPile fit to load distribution
The butler The differentiation did it
42
0
500
1,000
1,500
2,000
0 10 20 30 40 50
LO
AD
at P
ILE
HE
AD
(kN
)
PILE HEAD MOVEMENT (mm)
HEADTOE
300 mm diameter, 30 m long concrete pileE = 35 GPa; ß = 0.30; Strain-softening
SHORTENING
0
500
1,000
1,500
2,000
0 10 20 30 40 50
LO
AD
(kN
)
MOVEMENT (mm)
HEAD
SHAFTTOE
300 mm diameter, 30 m long concrete pileE = 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 30SEGMENT MOVEMENT AT MID-POINT (mm)S
EG
ME
NT
SH
AF
T R
ES
SIS
TA
NC
E A
T M
ID-P
OIN
T
(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
43
0
5
10
15
20
25
30
35
40
0 500 1,000 1,500 2,000 2,500 3,000D
EP
TH
(m
)
LOAD (kN)
FILLß = 0.30
SOFT CLAYß = 0.20
SILTß = 0.25
SANDß = 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 functionwith 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
LO
AD
(kN
)
MOVEMENT (mm)
Head-down static loading test load-movements
Head
Shaft
Toe
Compression
The simulations are made using UniPile Version 5
44
Arcos Egenharia
E-cell pileat
Rio Negro Ponte Manaus – Iranduba
Brazil
The bi-directional test
Arcos Egenharia de Solos Bidirectional test at
Rio Negro Ponte Manaus—Iranduba, Brazil
45 45
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
MO
VE
ME
NT
(m
m)
LOAD (tonne)
Test at Banco Europeu
Elisio (1983)
Pile PC-1June 3, 1981
Upward
Downward
11.0
m2.
0 mE
520 mm
Upward Load
THE CELL
Telltales
and
Grout Pipe
Pile Head
Downward Load
Typical Test Results (Data from Eliso 1983)
46 46
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”
47
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)
MO
VE
ME
NT
(m
m)
Upward
Downward
TEST DATA FITTED
TO TESTDATA
Example 1 Example 2
-80
-60
-40
-20
0
20
40
60
80
100
1200 2,000 4,000 6,000 8,000 10,000
MO
VE
ME
NT
(m
m)
LOAD (kN)
UPWARD
DOWNWARD
Weight ofShaft
Residual Load
Simulated curve
Simulated curve
48
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)
LO
AD
(K
N)
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 Upward curve only
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 jack engages the upper soils first, which are less stiff than the lower soils.
Head-down combining upward and downward curves
49
-15
-10
-5
0
5
10
15
20
25
0 100 200 300 400 500 600 700 800 900 1,000
MO
VE
ME
NT
(m
m)
LOAD (kN)
E
8.5
3.0
If unloaded after 10 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 = 0.30rt = 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
MO
VE
ME
NT
(m
m)
LOAD (kN)PCE-07
E
7.2
4.3
ß = 0.5 to 2.5 m δ = 5 mm ϴ = 0.30ß = 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.
50
0
500
1,000
1,500
2,000
2,500
3,000
0 5 10 15 20 25 30
LO
AD
(kN
)
MOVEMENT (mm)
PCE-02
PCE-07
Max downward movement
Max upwardmovement
Max upwardmovement
Max downwardmovement
Pile PCE-02Compression
PCE-02, Toe
PCE-07, Toe
PCE-02 and -07Shaft
0
2
4
6
8
10
12
0 400 800 1,200 1,600
DE
PT
H (
m)
LOAD (kN)
PCE-07
PCE-02
0
5
10
15
20
25
30
0 400 800 1,200 1,600
MO
VE
ME
NT
(m
m)
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
51 51
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
52 52
0
5
10
15
20
25
30
0 10 20 30Cone Stress, qt (MPa)
DE
PTH
(m
)
0
5
10
15
20
25
30
0 200 400 600 8001,00
0
Sleeve Friction, fs (KPa)
DE
PTH
(m
)
0
5
10
15
20
25
30
-100 0 100 200 300 400 500
Pore Pressure (KPa)
DE
PTH
(m
)
0
5
10
15
20
25
30
0 1 2 3 4 5
Friction Ratio, fR (%)
DE
PTH
(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.
53
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 6,000M
OV
EM
EN
T (
mm
)LOAD (kN)
ELEV.(m)
#5
#4
#3
#2
#1
Pile Toe Elevation
54 54
Load Distribution cnt.
0
5
10
15
20
25
0 5 10 15 20
LOAD (MN)D
EP
TH (
m)
O-cellCell Level
0
5
10
15
20
25
0 5 10 15 20
LOAD (MN)D
EP
TH (
m)
ß = 0.75
ß = 0.35
0
5
10
15
20
25
0 5 10 15 20
DE
PT
H (
m)LOAD (MN)
ß = 0.65
Residual
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 25 m depth
55
0
5
10
15
20
25
0 5 10 15 20 25
DE
PT
H (
m)
Cone Stress, qt (MPa)
0
5
10
15
20
25
0 20 40 60 80 100D
EP
TH
(m
)
Sleeve Friction, fs (kPa)
0
5
10
15
20
25
0 50 100 150 200 250
DE
PT
H (
m)
Pore Pressure (kPa)
0
5
10
15
20
25
0.0 0.5 1.0 1.5 2.0
DE
PT
H (
m)
Friction Ratio, fR (%)
0
5
10
15
20
25
0 10 20 30 40 50
DE
PT
H (
m)
N (blows/0.3m)
compact SAND
CLAY
compact SAND
dense SAND
The soil profile determined by CPTU and SPT
56
0
5
10
15
20
25
0 5 10 15 20 25
DE
PT
H (
m)
Cone Stress, qt (MPa)
0
5
10
15
20
25
0 20 40 60 80 100D
EP
TH
(m
)
Sleeve Friction, fs (kPa)
0
5
10
15
20
25
0 50 100 150 200 250
DE
PT
H (
m)
Pore Pressure (kPa)
0
5
10
15
20
25
0.0 0.5 1.0 1.5 2.0
DE
PT
H (
m)
Friction Ratio, fR (%)
0
5
10
15
20
25
0 10 20 30 40 50
DE
PT
H (
m)
N (blows/0.3m)
compact SAND
CLAY
compact SAND
dense SAND
The results of the bidirectional test
57
-50
-40
-30
-20
-10
0
10
20
30
40
50
0 200 400 600 800 1000 1200
MO
VE
ME
NT
(m
m)
LOAD (kN)
Pile HeadUPWARD
BDC DOWNWARD
15.0
m6.
0 m
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.
58
t-z and q-z Functions
SAND ABOVE BDCRatio function
Exponent: θ = 0.55δult = 35 mm
SAND BELOW BDCRatio function
Exponent: θ = 0.25δult = 40 mm
TOE RESPONSERatio function
Exponent: θ = 0.40δult = 40 mm
CLAY (Typical only, not used in the
simulation) Exponential functionExponent: b = 0.70
The final fit of simulated curves to the measured
59
-50
-40
-30
-20
-10
0
10
20
30
40
50
0 200 400 600 800 1,000 1,200
MO
VE
ME
NT
(m
m)
LOAD (kN)
Pile HeadUPWARD
BDC DOWNWARD
15.0
m6.
0 m
0
5
10
15
20
25
0 200 400 600 800 1,000
DE
PT
H (
m)
LOAD (kN)
BDC load
0
5
10
15
20
25
0 10 20 30 40 50
DE
PT
H (
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.
60
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
LOA
D (k
N)
MOVEMENT (mm)
EquivalentHead-Down test
HEAD
TOE
Pile head movement for 30 mm pile toe
movement
Pile head movement for 5 mm pile toe movement
61
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.
62
Thank you for your attention