basics of design of piled foundations-bengt h.fellenius

1BASICS OF DESIGN OF PILED

FOUNDATIONS

Bengt H. Fellenius

Brisbane November 28, 2008

22

Morning

08:00h Registration

08:30h The Static Loading Test and Other Testing Methods

09:40h Break

10.00h The Bi-directional Test the O-cell

11:00h Brief Background to Basic PrinciplesApplicable to Piled Foundations

12.00h LUNCH

SCHEDULE

Afternoon

13:00h Piles and Pile GroupsLong-term Behaviorand How We Know What We Know

14:10h Break

14:30h Analysis of Load Transfer and Capacity of Piles

15:40h Unified Design of Piles and Pile Groups

16.45h Questions and Discussions

17:30h End of Day

33

www.Fellenius.net

44

Brisbane

Power Point Slides1-Static_Test.pdf 2-Background.pdf 3-Case_Histories.pdf 5-Analysis.pdf 6-Unified_Method.pdf

UniSoft ProgramsInformation and Order Form UniBear.zip UniCone.zipUniPhase.zip UniPile.zip UniSettle.zip

55

BASICS OF DESIGN OF PILED

FOUNDATIONS

Bengt H. Fellenius

The Static Loading TestPerformance, Instrumentation, Interpretation

Brisbane November 28, 2008

99

Candidates for Darwin Award, First Class

1010

! ! !Testing piles is a risky business.

1111

4. JACK

3. LOAD CELL

2. SPACER

1. SWIVEL PLATE

What do you think could happen to the stack of four pieces on the pile head when the load is applied? And, therefore, to the three oblivious persons next to the pile?

1212This is how experience taught the three, and others, to arrange the units on the pile head

1313

Better safe than sorry!

2121

Fellenius 1984

2222

0

50

100

150

200

250

300

350

0 2,000 4,000 6,000 8,000 10,000Loadcell (KN)

E

r

r

o

r

i

n

J

a

c

k

L

o

a

d

(

K

N

)

Head-down O-cell Pile

August 2006

2.5% Error

The error can be small or it can be large. Here are results from two tests at the same site using the same equipmenttesting two adjacent piles, one after the other.

0

500

1,000

1,500

2,000

0 5,000 10,000 15,000Loadcell load (KN)

E

r

r

o

r

(

K

N

)

15% Error

2.5% Error

Shinho-Pile August 2006

Note, the test on the pile called "O-cell pile" is a head -down test after a preceding O-cell test.

2323

A routine static loading test provides the load-movement of the pile head...

and the pile capacity?

2424

The Offset Limit MethodDavisson (1972)

OFFSET (inches) = 0.15 + b/120

OFFSET (SI-unitsmm) = 4 + b/120

b = pile diameter (inch or mm)

LLEAQ

Q

L

2525

The Decourt ExtrapolationDecourt (1999)

0 100 200 300 400 5000

500,000

1,000,000

1,500,000

2,000,000

LOAD (kips)

L

O

A

D

/

M

V

M

N

T

-

-

Q

/

s

(

i

n

c

h

/

k

i

p

s

)

Ult.Res = 474 kips

Linear Regression Line

Q

1

2

CC

Qu C1 = Slope

C2 = Y-intercept

Q

2626

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)

2727

DECOURT 235

2828

0

500

1,000

1,500

2,000

2,500

0 5 10 15 20 25 30 35 40

MOVEMENT (mm)

L

O

A

D

(

K

N

)

Offset-LimitLine

Definition of capacity (ultimate resistance) is only needed when the actual value is not obvious from the

load-movement curve

2929

Pile E29.5-inch closed-toe pipe

Some results from Jones Island, Milwaukee

on 30 m to 50 m long driven piles (Fellenius et al., 1983)

3030

Pile B212HP63

3131

Pile Toe Movement

0 5 10 15 20 25 300

1,000

2,000

3,000

4,000

MOVEMENT (mm)

L

O

A

D

A

T

P

I

L

E

H

E

A

D

(

K

N

) HEAD

HEAD LOAD vs. TOE MOVEMENT 65 ft long, 14 inch pipe pile.

With a telltale to the toe arranged to determine pileshortening. Dont have it measure toe movement directly.

3232

Analysis of toe resistance

An adjacent pull test on a similar instrumented pile established that the pile shaft resistance is about 2,000 KN approximately fully mobilized just short of 5-mm toe movement. The thereafter applied load in the push test goes to toe resistance, only.0 5 10 15 20 25 30

0

1,000

2,000

3,000

4,000

MOVEMENT (mm)

L

O

A

D

A

T

P

I

L

E

H

E

A

D

(

K

N

)

HEAD

HEAD LOAD vs. TOE MOVEMENT

ESTIMATED TOE LOAD vs.

TOE MOVEMENT(Based on the assumption thatshaft resistance is 2,000 KN)

+10 %

-10 %

PILE SHORTENING

3333

20 inch square diameter, prestressed concrete pile driven to 58 ft embedment, through about 45 ft of soft silt and

clay, 5 ft of sand, and to bearing 6 ft into hard clay

0

100

200

300

400

500

600

0.0 0.2 0.4 0.6 0.8 1.0 1.2

MOVEMENT (in)

L

O

A

D

(

k

i

p

s

)

Push test three months after driving

Pull test five

months after

driving

Data from AATech Scientific Inc.

PUSH and

PULLTo separate

shaft and toe resistances. The pile is

equipped with a toe telltale.

Unloading-reloading once or a couple of times on the way upserves no purpose and may result in distorted analysis results

3434

Combining the push and pull test results with the telltale measurements to calculate the load-movement for the pile toe

Data from AATech Scientific Inc.

0

100

200

300

400

500

600

0.0 0.2 0.4 0.6 0.8 1.0 1.2

MOVEMENT (in)

L

O

A

D

(

k

i

p

s

)

PUSH; HEAD

TOE

"Toe Telltale "

PULL; HEADSHAFT

3535

It is not possible to interpret more than very approximately from the load-movement curve how much of the pile capacity that is toe resistance and how much is shaft resistance.

Suggestions for Routine Testing

Adding occasional unloading and re-loading cycles only distorts the figure. Cyclic loading requires a multitude of identical cycles maybe cycle 100 times at each load and unload magnitude, and cycle at several load levels. This is not practical for routine tests, but anything less is waste of effort.

The standard method of eight increments up to a maximum load is probably the worst method of the lot. Instead of applying one increment each hour (as a shock to the pile), use one a quarter of the increment size and apply one every 15 minutes a much more gentle approach. Or, one small increment every 10 minutes aim for a total of about 30 increments; a five-hour test duration.

On reaching the maximum load and holding it (say, for 10 minutes), unload in, say five or six decrements.

3636

The routine static loading test with load applied to the pile head and movement measured only at the pile head provides very limited information Good enough for proof testing. However, if more information is desired, instrument the test pile, or run an O-cell test.

3737

Instrumentation

and

Interpretation

3838

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?

3939

Load distribution for constant unit shaft resistance

0

50

100

0 100

h A2

LOAD, Q

A1

Midheight

Average Load 0

LoadDistribution

Q = az

DEPTH, z

PILE HEAD

PILE TOE

ars

4040

Linearly increasing unit shaft resistanceand its load distribution

00 Unit Shaft

Resistance

h

az

DEPTH, z

31

3axA

21 AA hhX 58.0

3X is where the average load should be plotted

6)23(2

323 xhxhaA

00 Average

LoadLOAD, Q0

A1

A2

LoadDistribution

Q = az2/2

x

h

4141

Today, telltales are not used for determining strain (load) in a pile because using strain gages is a more assured, more accurate, andcheaper 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 vibratory 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.

4343

Rebar Strain Meter Rebar Strain Meter Sister BarSister Bar

Reinforcing Rebar

Rebar Strain Meter

Wire Tie

Instrument Cable

or Strand

Tied to Reinforcing Rebar

Hayes 2002

Three bars?!

Wire Tie

Tied to Reinforcing Rings

Reinforcing Rebaror Strand

(2 places)

Rebar Strain Meter

Instrument Cables

(3 places, 120 apart)

4444

We have got the strain.How to we get the load?

Load is stress times area

Stress is Modulus (E) times strain

The modulus is the key

E

4545

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 steelAs = area of steelEc = modulus for concreteAc = area of concrete

4646

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 knowntE

4747

0 200 400 600 8000

10

20

30

40

50

60

70

80

90

100

MICROSTRAIN

T

A

N

G

E

N

T

M

O

D

U

L

U

S

(

G

P

a

)

Level 1

Level 2

Level 3

Level 4

Level 5

Best Fit Line

Example of Tangent Modulus Plot

4848

baddEt

ba

22

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

4949

0 200 400 600 8000

10

20

30

40

50

60

70

80

90

100

MICROSTRAIN

T

A

N

G

E

N

T

M

O

D

U

L

U

S

(

G

P

a

)

Level 1

Level 2

Level 3

Level 4

Level 5

Best Fit Line

Example of Tangent Modulus Plot

Intercept is

b

Slope is a

5050

Note, just because a strain-gage has registered some strain values during a test does not guarantee that the data are useful. Unavoidable errors and natural variations amount to about 50 microstrain to 100 microstrain. Therefore, the test must be designed to achieve strain values at least of about 500 microstrain and beyond. If the imposed strain 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.

5151

Example of evaluation and assessment of strain-gage values

Bored Pile, Singapore, 2007

#1

#13

#8

#7

#6

#5

#4

#3

#2

#9

#12

#11

3

7

.

5

m

(

1

2

3

f

t

)

1,000 mm (39 in )

S

t

i

f

f

m

a

r

i

n

e

c

l

a

y

S

a

p

r

o

l

i

t

e

S

a

n

d

,

S

i

l

t

,

a

n

d

c

l

a

y

a

s

m

a

t

r

i

x

i

n

w

e

a

t

h

e

r

e

d

g

r

a

n

i

t

i

c

b

e

d

r

o

c

k

Pair of Vibrating-WireStrain Gages (Sister Bars)

1,000 mm (39 in.)

0

2

4

6

8

10

12

0 5 10

5252

UTP-3 Load-Movement

0

5

10

15

20

25

0 5 10 15 20 25

MOVEMENT (mm)

L

O

A

D

(

M

N

)

UTP-3 Load-Strain

0

5

10

15

20

0 200 400 600 800 1,000STRAIN ()

P

I

L

E

H

E

A

D

L

O

A

D

(

M

N

)

SG-1

SG-2

SG-3

SG-4

SG-5

SG-6

SG-7

SG-8

SG-9

SG-11

SG-12

SG-13

1 2 3 4 5 7 6 8 11 9 12 13 Gage Levels

5353

STAGE II, Tangent ModulusPile diameters are all equal to nominal value (1.00 m)

10

15

20

25

30

35

40

45

50

0 200 400 600 800 1,000 1,200

STRAIN ()

/

SG-13

SG-12

SG-11

SG-9

SG-8

SG-7

SG-6

Tangent Modulus Lines

Strains are as measured; all pile diameters are assumed to be equal to the nominal area

5454

UTP-3 Load-Strain for adjusted areas

0

5

10

15

20

25

0 200 400 600 800 1,000 1,200STRAIN ()

P

I

L

E

H

E

A

D

L

O

A

D

(

K

N

)

SG-13

SG-12

sg-(11)

sg-(9)

SG-8

sg-(7)

sg-(6)

SG-5

SG-4

SG-3

3 4 5 6 7 8 9 11 12 13 ////

//

In a trial-and-error approach, the piles diameters (pile areas) were adjusted, and the strains were proportioned to the adjusted pile areas to ensure parallel slope of load-strain curves and equal tangent modulus lines.

Adjustments ranged from increasing the diameter by 110 mm (#6) through 280 mm (#7)

5555

STAGE II, Tangent ModulusPile diameters are adjusted

10

15

20

25

30

35

40

45

50

0 200 400 600 800 1,000 1,200

STRAIN ()

/

SG-13

SG-12

SG-11

SG-9

SG-8

SG-7

SG-6

Note, you can also plot the tangent-modulus lines as tangent-stiffness (AE) lines, i.e., plot change of load over change of strain as opposed to change of stress over change of strain. Then, use the AE-values directly in the load calculation. However, this does give you less reference to what the actual differences are along the pile.

5656

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25

LOAD (MN)

D

E

P

T

H

(

m

)

UTP-3

Shaft Resistance is not fully mobilized below 20 m depth.

Now, having determined the

relation between strain and

secant modulus (from knowing

the tangent-modulus), we are

ready to convert measured

strain to measured load in the

pile: The load distribution.

Marine clay

Saprolitic soil

5757

What we measure is the increase of

load in the pile due to the load applied

to the pile head. What about the

external-origin load in the pile that

was there before we started the test?

That is, the Residual load.

5858

Normalized Applied Load

D E P T H

Load distributions in

static loading tests on

four instrumented

piles in clay

5959

B. Load and resistance in DA

for the ultimate load applied

Sand

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

E

P

T

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)

D

E

P

T

H

(

m

) True

Residual

True minus Residual

A. Distribution of residual load in DA and BC

before start of the loading test

6060

0

5

10

15

20

25

30

35

40

45

50

0 500 1,000 1,500 2,000 2,500LOAD (KN)

D

E

P

T

H

(

m

)

Fellenius et al. 2004

Static Loading Testat Pend Oreille,

Sandpoint, Idaho, for the realignment of US95

406 m diameter,45 m embedment,

closed-toe pipe pile driven in soft clay

Clay

200+ m

6161

Distribution of Measured Loads (False Resistance)and True Resistance

0

5

10

15

20

25

30

35

40

45

50

0 500 1,000 1,500 2,000 2,500LOAD (KN)

D

E

P

T

H

(

m

)

True ResistanceFrom Test data and from Calculations

Residual LoadFrom Test data and from Calculations

Measured LoadFrom Test data and from Calculations

Fellenius et al. 2004

6262

FHWA tests on 0.9 m diameter bored pilesOne in sand and one in clay

(Baker et al., 1990 and Briaud et al., 2000)

0

2

4

6

8

10

12

0 10 20 30 40

Cone Stress and SPT N-Index(MPa and bl/0.3 m)

D

E

P

T

H

(

m

)

Silty Sand

Sand

Pile 4

0

2

4

6

8

10

12

0 10 20 30 40

Cone Stress (MPa)

D

E

P

T

H

(

m

)

Pile 7

N

qc

ClaySilty

Sand Clay

6363

RESULTS: Load-transfer curves

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 1,000 2,000 3,000 4,000 5,000

LOAD (KN)

D

E

P

T

H

(

m

)

PILE 4SAND

Measured Distribution

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 1,000 2,000 3,000 4,000 5,000

LOAD (KN)

D

E

P

T

H

(

m

)

PILE 4SAND

True Distribution

Residual Load


0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 1,000 2,000 3,000 4,000 5,000

LOAD (KN)

D

E

P

T

H

(

m

)

PILE 7CLAY


0.0

2.0

4.0

6.0

8.0

10.0

12.0

0 1,000 2,000 3,000 4,000 5,000

LOAD (KN)

D

E

P

T

H

(

m

)

PILE 7CLAY

True Distribution

Residual Load

6464

Results of analysis of a Monotube pile in sand(Fellenius et al., 2000)

0

5

10

15

20

25

0 1,000 2,000 3,000

LOAD (KN)

D

E

P

T

H

(

m

)

True Resistance

Measured Resistance

Residual Load

6565

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)

D

E

P

T

H

(

m

)

Measured Shaft ResistanceDivided by 2

Residual Load

Measured Load

True Resistance

ExtrapolatedTrue Resistance

Shaft Resistance

6666

Analysis Procedure0

2

4

6

8

10

12

14

16

18

20

0 500 1,000 1,500

LOAD (KN)

D

e

p

t

h

(

m

)

Residual Load

True Resistance

Measured Load

Extension of Matching

Shaft ResistanceDistributionDivided by 2

Fellenius 2002

6767

Results

0

2

4

6

8

10

12

14

16

18

20

0 500 1,000 1,500 2,000

LOAD (KN)

D

e

p

t

h

(

m

)

CAPWAPDeterminedResistance

True Resistance

Residual

CAPWAP ShaftDivided by 2

True ShaftResistance

Fellenius 2002

6868

0

200

400

600

800

1,000

0 5 10 15 20 25 30

MOVEMENT (mm)

L

O

A

D

(

K

N

)

No Residual Load

Residual Load present

OFFSET LIMIT LOAD

No Strain Softening

Presence of residual load is not just of academic interest

0

200

400

600

800

1,000

0 5 10 15 20 25 30

MOVEMENT (mm)

L

O

A

D

(

K

N

)

With Strain Softening

Residual Load present

No Residual Load

OFFSET LIMIT LOAD

6969

0

200

400

600

800

1,000

1,200

0 5 10 15 20 25

MOVEMENT (mm)

L

O

A

D

(

K

N

)

HEAD

TOE

TOE TELLTALEA

Does not this shape of measured toe movement suggest that there is a distinct toe capacity?

Toe Resistance

7070

0

200

400

600

800

1,000

1,200

0 5 10 15 20 25

MOVEMENT (mm)

L

O

A

D

(

K

N

)

HEAD

TOE

TOE TELLTALEA

0

200

400

600

800

1,000

1,200

0 5 10 15 20 25

MOVEMENT (mm)

L

O

A

D

(

K

N

)

HEAD

"Virgin" Toe Curve

TOE

B

No, it only appears that way when we forget to consider the residual toe load (also called the initial, or virgin toe movement)

7171

Residual Load is the same as Drag Load. The distinction made is that by residual load we mean the locked-in load present in the pile immediately before we start a static loading test. By drag load we mean the load present in the pile in the long-term

Residual load

Residual load as well as drag load can develop in coarse-grained soil just as it does in clay soil

Both residual load and dragload develop at very small movements between the pile and the soil

7272

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 relative the no-load situation (i.e., when no external load acts at the gage location).

7373

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 hte pile will impose loads on the pile.

7474

0

5

10

15

20

25

30

35

40

45

50

55

60

-300 -200 -100 0 100 200 300 400

STRAIN ()

D

E

P

T

H

(

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

Strain measured during the 218-day wait-period between driving (grouting) and testing.

Do these strains really represent load in the pile, as present before the start of the static loading test?

7575

Concrete curing 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

T

E

M

P

E

R

A

T

U

R

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

7676

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35

DAY AFTER GROUTING

T

E

M

P

E

R

A

T

U

R

E

(

C

)

Start of Static Loading Test

Temperatures measured in a 74.5 m long, 2.6 m diameter bored pile

10

20

30

40

50

60

70

0 1 2 3 4 5

DAY AFTER GROUTING

T

E

M

P

E

R

A

T

U

R

E

(

C

)

Temperatures measured in a 74.5 m long, 2.6 m diameter bored pile

Temperature records during curing of grout in the Golden Ears Bridge test pile, Vancouver, BC. Data courtesy of Trow Engineering Inc. and Amec Inc.

7777

-400

-300

-200

-100

0

100

0 5 10 15 20 25 30 35DAY AFTER GROUTING

C

H

A

N

G

E

O

F

S

T

R

A

I

N

(

)

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 curing of grout in the Golden Ears Bridge test pile

7878

-200

-150

-100

-50

0

50

100

0 100 200 300 400 500Time (days)

S

T

R

A

I

N

(

)

SNEW

Pile piece submerged

INCREASING TENSION

Concrete Cylinder Piece

Submerging the short pile segment, letting it swell from absorption of water

7979

The strain gages are not temperature sensitive, but the strain measurements 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, for lower quality vibrating wire gages, 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. (A routine measure of Geokon, US manufacturer of vibrating wire gages).

8080

Readings should be taken immediately before (and after) every event of the piling work and not just during the actual loading test

A series of 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

8181

Of course,

we must consider also other aspects:

8282

Interpretation of a series of testsperformed at different times

0 10 20 30 40 50 60 700

10

20

30

40

50

60

70

Movement (mm)Ch

a

n

g

e

o

f

H

o

r

i

z

o

n

t

a

l

S

t

r

e

s

s

(

K

P

a

)

5 Days1 Day8 Days4 Months22 Months

Cell D1

Results thought due to set-up and explained as Increase inHorizontal Effective Stress

Fellenius 2002

Results plotted According to Movement Path

0 50 100 150 200 2500

10

20

30

40

50

60

70

Movement (mm)

5 Days1 Day8 Days4 Months22 Months

8383

Also the best field work can get messed up if the analysis and

conclusion effort loses sight of the history of the data

The dynamic test (CAPWAP) was performed after the static test.

The redriving (ten blows) forced the pile down additionally about 45 mm.

0

500

1,000

1,500

2,000

0 100 200 300

MOVEMENT (mm)

L

O

A

D

(

K

N

)

STATIC TEST

DYNAMIC TEST

0

500

1,000

1,500

2,000

0 100 200 300

MOVEMENT (mm)

L

O

A

D

(

K

N

)

DYNAMIC TEST

0

500

1,000

1,500

2,000

0 100 200 300

MOVEMENT (mm)

L

O

A

D

(

K

N

)

DYNAMIC TEST in a series of blows

Repeated STATIC TEST

84

Result on a test on a 2.5 m diameter, 85 m long bored pile

0 50 100 150 200 2500

10

20

30

Movement (mm)

L

o

a

d

(

M

N

)

LEVEL A Downward, STAGES 1 and 5

Test Data

FE analysis

Does unloading/reloading add anything of value to a test?

8585

The above series of unloading/reloading has added nothing but cost the client a lot of money.

0

500

1,000

1,500

2,000

0 1 2 3 4

MOVEMENT (mm)

L

O

A

D

(

K

N

)

8686

Good measurements do not guarantee good conclusions!

A good deal of good thinking is necessary, too

8787

Results of loading tests on 40 m long,

instrumented steel piles 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)

D

E

P

T

H

(

m

)

0

5

10

15

20

25

30

35

40

0 50 100 150 200 250

UNIT SHAFT SHEAR (KPa)

D

E

P

T

H

(

m

) ?

8888

0

5

10

15

20

25

30

35

40

45

0 2,000 4,000 6,000 8,000 10,000

LOAD (KN)

D

E

P

T

H

(

m

)

= 0.3

= 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


D

E

P

T

H

(

m

)

= 0.3

= 0.4

8989

And a second pile:

0

5

10

15

20

25

30

35

40

45

0 50 100 150 200 250 300 350 400 450


D

E

P

T

H

(

m

)

= 0.3

= 0.5

0

5

10

15

20

25

30

35

40

45

0 2,000 4,000 6,000 8,000 10,000

LOAD (KN)

D

E

P

T

H

(

m

)

= 0.3

= 0.5

9090Jorj Osterberg 2001

The Bi-Directional

Static Loading Test

The O-cell Test

9191

Schematics of the Osterberg O-Cell Test(Meyer and Schade 1995)

Upward Load

Downward Load

THE O-CELL

Telltales

and

Grout Pipe

Pile Head

9292

Three O-Cells inside the reinforcing cage(My Thuan Bridge, Vietnam)

9494

The O-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.

95O-cell in a pipe pile inserted in a augercast pile after grouting.

9696Inchon, Korea

9797

-60-50-40-30-20-10

010203040506070

0 5,000 10,000 15,000 20,00M

o

v

e

m

e

n

t

(

m

m

)

Load (KN)

Upward

Downward

Upward

Approximate extension of the toe movement to the zero conditions

EXAMPLE 1Results of an O-cell test on a 2.8 m by 0.8 m, 4 m deep barrette in Manila, Philippines

9898

O-Cell test on a 1,250 mm

diameter, 40 m long, bored pile at US82 Bridge in Washington,

Mississippi 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)

M

O

V

E

M

E

N

T

(

m

m

)

UPPER PLATE UPWARD MVMNT

LOWER PLATE DOWNWARD MVMNT

Weightof

Shaft

Residual Load

Shaft

Toe

EXAMPLE 2

9999

Resistance Distribution

0

5

10

15

20

25

30

35

40

0 2,000 4,000 6,000 8,000 10,000

LOAD (KN)

D

E

P

T

H

(

m

)

Strain-Gage Level #4




O-Cell Level

Pile Toe

Clay Silt

Sandy Silt

Dense Sand with

Gravel

The unit shear resistance at shaft failure corresponds to a beta coefficient of about 1.0.

0

5

10

15

20

25

30

35

40

0 100 200 300 400AVERAGE UNIT SHAFT RESISTANCE (KPa)

D

E

P

T

H

(

m

)

G.W.

100100

Load-Movement Curves

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

0 20 40 60 80 100 120

MOVEMENT (mm)

L

O

A

D

(

K

N

)




O-Cell

101101

Searching for the Residual Load

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

0.0 0.5 1.0 1.5 2.0

PILE COMPRESSION (mm)

L

O

A

D

(

K

N

)

INDICATED RESIDUAL LOAD

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

0.0 25.0 50.0 75.0 100.0 125.0 150.0

PLATE SEPARATION (OPENING) (mm)L

O

A

D

(

K

N

)

O-Cell LoadO-Cell Load

102102

From the O-Cell results, one can produce the load-movement curve that one would have obtained in a routine Head-Down Test

Head down

103103

104104

O-Cell Results Shown Two Ways

-80

-60

-40

-20

0

20

40

60

80

100

120

0 2,000 4,000 6,000 8,000 10,000

LOAD (KN)

M

O

V

E

M

E

N

T

(

m

m

)

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

0 20 40 60 80 100 120

MOVEMENT (mm)

L

O

A

D

(

K

N

)

Shaft Movement

Toe Movement

Weight of Shaft

Residual Load

105105

O-Cell test on a 43 ft long pile socketed into chalk bedrock

at US82, Bridge at

Oktebbeha, MS

-1

0

1

2

3

4

5

0 500 1,000 1,500

LOAD (tons)

M

O

V

E

M

E

N

T

(

i

n

c

h

e

s

)

LOWER PLATE DOWNWARD MVMNT

UPPER PLATE UPWARD MVMNT

EXAMPLE 3

106106

Measured Resistance Distribution

0

5

10

15

20

25

30

35

40

45

0 400 800 1,200 1,600

LOAD (tons)

D

E

P

T

H

(

f

e

e

t

)

Clay and

Sand

ChalkBed-rock



Strain-GageLevel #1

O-Cell Level

107107

Shaft Shear Distribution

0

5

10

15

20

25

30

35

40

45

0 5 10 15AVERAGE UNIT SHAFT RESISTANCE (ksf)

D

E

P

T

H

(

f

e

e

t

)

Clay and

Sand

ChalkBed-rock

O-Cell Level

O-Cell & Level #1

Levels #2 & #3

Level #1 & #2

Ground & Level #1

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25

AVERAGE UNIT SHAFT RESISTANCE (ksf)

D

E

P

T

H

(

f

e

e

t

)

ChalkBed-rock

Clay and

Sand

O-Cell

#1 to Cell

#2 to #1

#3 to #2

AFTER CORRECTION FOR

RESIDUAL LOAD

Estimated Residual Shear

Ground to #3

Residual Load not considered Corrected for Residual Load

108108

0 2 4 6 8 10 12 14 16-80

-70

-60

-50

-40

-30

-20

-10

0

10

20

APPLIED LOAD (MN)

M

O

V

E

M

E

N

T

(

m

m

)

RE

BO

UN

D W

HE

NU

NL O

AD

ING

COMPRESSION OFSOFT SOIL AT TOE

Toe load-movement for a pile with a soft toe at Albuquerque, New Mexico (Data from Osterberg and Hayes, 1999)

Example 4

Finding a soft toe

109109

Kahuku Bridge across Kamehameha Highway, Hawaii

Test on 600 mm, 17 m long, bored pile in hard clay and weathered rock

EXAMPLE 5

-1

0

1

2

3

4

5

6

7

0 50 100 150 200 250 300 350 400

O-cell Load (kips)

M

O

V

E

M

E

N

T

(

i

n

c

h

e

s

)

UPWARD

DOWNWARD

110

0

10

20

30

40

50

60

70

80

0 100 200 300 400 500 600 700 800

LOAD (kips)

D

E

P

T

H

(

f

t

)

DATA FROM O-CELL TEST

O-cell

Shaft and toe resistances are not fully mobilized below the O-cell

Silty hard clay

Weathered rock

Silty stiff clay

0

10

20

30

40

50

60

70

80

0 100 200 300 400 500 600 700 800

LOAD (kips)

D

E

P

T

H

(

f

t

)

CONVERTED TO HEAD-DOWN "TEST"

APPROXIMATED

SPECULATIVE FULLY MOBILIZED

O-cell

1,000

The load distribution after tangent-modulus evaluation of pile stiffness

The "head-down" load distribution and speculative fully mobilized resistance

Buoyant Weight

111111

EXAMPLE 6

Test at Bangkok Airport

112112

Stage 1Lower Cell activatedUpper cell closed

Stage 2Lower Cell openUpper Cell activated

Stage 2Lower Cell closedUpper Cell activated

Data fromFox, I., Du, M. and Buttling,S. (2004)Buttling, S. (2006)

113113

Downward load-movements during test phases 1, 2, and 3.

Concern was expressed (Buttling 2006) that the toe resistance (Phase 1) was 3,000 KN and the shaft resistance for the lower segment was 5,000 KN (Phase 2), while in Phase 3 the combined shaft and toe resistances were only 6,000 KN. Should not the Phase 3 resistance be 8,000 KN rather than 6,000 KN (i.e., the sum of the values 5,000 KN and 3,000)?

0

25

50

75

100

125

150

175

0 2,000 4,000 6,000 8,000 10,000

LOAD (KN)

M

O

V

E

M

E

N

T

(

m

m

)

Active CellInactive, Open CellInactive, Closed Cell

P1 P2P3

1 2 3

3,000 KN

5,000 KN6,000 < 8,000 KN??

114114

Downward toe movements

0

25

50

75

100

125

150

175

0 2,000 4,000 6,000 8,000 10,000

LOAD (KN)

M

O

V

E

M

E

N

T

(

m

m

)


P1 P2P3

1 2 30

25

50

75

100

125

150

175

0 2,000 4,000 6,000 8,000 10,000

LOAD (KN)

D

O

W

N

W

A

R

D

M

O

V

E

M

E

N

T

(

m

m

)


P2

P1 and P2 data combined

P3

1 2 3

are best plotted per sequence of testing. Particularly when considering the example toe resistance, one must evaluate the load-movement response in comparing Phase 1 + Phase 2 to Phase 3 (i.e., P2 shaft below cell plus P1 toe).

115115

O-Cell tests for Hacienda Elena Development, Guaynabo, Puerto Rico

EXAMPLE 7

116116

Clayey Silt

Saprolite

Hard Clay

Weathered Bedrock

O-cell Test Results

-80

-70

-60

-50

-40

-30

-20

-10

0

10

20

0 1,000 2,000 3,000 4,000 5,000

LOAD (KN)

M

O

V

E

M

E

N

T

(

m

m

)

117117

Measured load-movements can besimulated (fitting) to t-z and q-z relations

Pile shaft by t-z relation; Pile toe by q-z relation

0 20 40 60 80 1000

20

40

60

80

100

Movement (%)

R

e

s

i

s

t

a

n

c

e

(

%

)

Exp. = 0.75

Exp. = 0.05

R = MVMNT^Exp

Exp. = 0.50

Exp. = 0.33

Exp. = 0.20

Exp. = 0.10

TOE

SHAFT

exp2

1

2

1 )(

RR

118118

O-cell Test Resultswith UniPile Simulation

0

5,000

10,000

15,000

0 10 20 30 40 50 60 70

MOVEMENT (mm)

L

O

A

D

(

K

N

)

Toe

Shaft

Exp.= 0.20

Exp.= 0.55


0

5,000

10,000

15,000

0 10 20 30 40 50 60 70

MOVEMENT (mm)

L

O

A

D

(

K

N

) Head

Toe

Shaft

Extrapolation ofO-cell data

Exp.= 0.20

Exp.= 0.55

Fitting Results


0

5,000

10,000

15,000

0 10 20 30 40 50 60 70

MOVEMENT (mm)

L

O

A

D

(

K

N

) Head

Toe

Shaft

Extrapolation ofO-cell data

Exp.= 0.20

Exp.= 0.55

Combining the t-z and q-z

curves

119119

Pensacola, Florida410 mm diameter, 22 m long, precast concrete pile driven into silty sand

EXAMPLE 8

120120

Pensacola, Florida, USA

-10

0

10

20

30

40

50

60

0 500 1,000 1,500 2,000 2,500

LOAD (KN)

M

O

V

E

M

E

N

T

(

m

m

)

121121

Bridge over Panama Canal, Paraiso Reach, Republic of PanamaO-cell test on a 2.0 m (80 inches) diameter, 30 m (100 ft) deep shaft

drilled into the Pedro Miguel and Cucaracha formations, February 2003.

EXAMPLE 9

122122

O-cell

Strain-Gage Locations

-50

-40

-30

-20

-10

0

10

20

30

40

50

0 5,000 10,000 15,000 20,000

LOAD (KN)

M

O

V

E

M

E

N

T

(

m

m

)

Downward Movement

Upward Movement

Load-Movements. Measured and Fitted to UniPile Calculation.

123123

Test Results Processed for Design Analysis

0

5

10

15

20

25

30

0 5,000 10,000 15,000 20,000 25,000 30,000

LOAD (KN)

D

E

P

T

H

(

m

)

0

5

10

15

20

25

30

0 5,000 10,000 15,000 20,000 25,000 30,000

LOAD (KN)

D

E

P

T

H

(

m

)

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

0 10 20 30 40 50 60 70

MOVEMENT (mm

L

O

A

D

(

K

N

)

)

Measured and Calculated Load-Movement Curvesplus Simulated Pile Head

Load-Movement

TOE

SHAFT

HEAD

Offset Limit

0.30

0.45

0.30

___

1.20

124124

Torre Chapultepec, Mexico City, Mexico

O-cell Test on a 700 mm diameter 34 m deep bored pile

0 m - 26 m desiccated clayey silt

5 m 34+ m dense sand and silt

EXAMPLE 10

125125


-400

-350

-300

-250

-200

-150

-100

-50

0

0 500 1,000 1,500 2,000 2,500

LOAD (KN)

D

O

W

N

W

A

R

D

M

O

V

E

M

E

N

T

(

m

m

)

O-cell Test?

126126


0

2,000

4,000

6,000

8,000

10,000

0 20 40 60 80 100 120 140

MOVEMENT (mm)

L

O

A

D

(

K

N

)

Head-Down Test

0

2,000

4,000

6,000

8,000

10,000

0 20 40 60 80 100 120 140

MOVEMENT (mm)

L

O

A

D

(

K

N

)

Head-Down Test


-400

-350

-300

-250

-200

-150

-100

-50

0

0 500 1,000 1,500 2,000 2,500

LOAD (KN)

D

O

W

N

W

A

R

D

M

O

V

E

M

E

N

T

(

m

m

)

O-cell Test

-400

-350

-300

-250

-200

-150

-100

-50

0

0 500 1,000 1,500 2,000 2,500

LOAD (KN)

D

O

W

N

W

A

R

D

M

O

V

E

M

E

N

T

(

m

m

)

O-cell Test

TOE MOVEMENT IN HEAD-DOWN TEST

128128

O-cell Tests on an 11 m long, 460 mm square precast concrete pile driven in silica sand in

North-East Florida(Data from Data from Bullock et al. 2005)

A study of Toe and Shaft Resistance

Response to Loading

EXAMPLE 11

129129

CPT sounding next to an 11 m long, 460 mm square precast concrete pile driven in silica sand in North-East Florida

Data from Bullock et al. 2005

0

2

4

6

8

10

12

14

0 10 20 30 40Cone Stress, qt (MPa)

D

E

P

T

H

(

m

)

0

2

4

6

8

10

12

14

0 100 200 300

Sleeve Friction (KPa)

D

E

P

T

H

(

m

)

0

2

4

6

8

10

12

14

0.0 0.2 0.4 0.6 0.8 1.0

Friction Ratio (%)

D

E

P

T

H

(

m

)

PRES

2b

130130

Load-movement curves for the pile toe.The two first cycles and beginning of the third cycleThe two first cycles and beginning of the third cycle

0

200

400

600

800

1,000

1,200

1,400

1,600

-3 -2 -1 0 1 2 3 4 5 6 7 8

TOE MOVEMENT (mm)

C

E

L

L

L

O

A

D

(

K

N

)

1

2

3

Toe Resistance Response

Data from

Bullock et al. 2005

131131

Load-movement curvesfor the pile toe during all four load cycles

0

200

400

600

800

1,000

1,200

1,400

1,600

-5 5 15 25 35 45 55 65 75

TOE MOVEMENT (mm)

C

E

L

L

L

O

A

D

(

K

N

)


132132

0

2

4

6

8

10

12

14

0 10 20 30 40Cone Stress, qt (MPa)

D

E

P

T

H

(

m

)

PRES

2b


133133

0

200

400

600

800

1,000

1,200

1,400

1,600

0 5 10 15 20 25 30 35 40 45 50

CELL EXTENSION (mm)

L

O

A

D

(

K

N

)

8 hours 4 days

16 days

SHAFT LOAD-MOVEMENT DIAGRAM FROM O-CELL TESTSPDA CAPWAP 18 min.BOR 1h BOR

EOD

Shaft Resistance Response

UPWARD MOVEMENT (mm)


134134

O-cell 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

EXAMPLE 12

135135

0

5

10

15

20

25

30

0 10 20 30Cone Stress, qt (MPa)

D

E

P

T

H

(

m

)

0

5

10

15

20

25

30

0 200 400 600 8001,00

0

Sleeve Friction, fs (KPa)

D

E

P

T

H

(

m

)

0

5

10

15

20

25

30

-100 0 100 200 300 400 500

Pore Pressure (KPa)

D

E

P

T

H

(

m

)

0

5

10

15

20

25

30

0 1 2 3 4 5

Friction Ratio, fR (%)

D

E

P

T

H

(

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

136136

-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

LOAD (KN)M

O

V

E

M

E

N

T

(

m

m

)

Pile Profile and O-cell Location O-cell Load-movement Up and Down

ELEV.(m)

#5

#4

#3

#2 #1

137137

Stress-Strain

0

1

2

3

4

5

0 10 20 30 40 50 60 70 80 90

STRAIN ()

S

T

R

E

S

S

(

G

P

a

)

Level 1

Level 2

Level 3

Level 4

Level 5

GL5 GL4

GL1 GL2 GL3

Results from Strain-gage Levels 1 through 5

Tangent Modulus

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70 80 90

STRAIN ()

T

A

N

G

E

N

T

M

O

D

U

L

U

S

,

M

t

(

G

P

a

)

Level 1Level 2Level 3Level 4Level 5Avg.Line

Et =39.5 - 0.06Es =39.5 - 0.03

138138

Load Distribution

0

5

10

15

20

25

0 5 10 15 20LOAD (MN)

D

E

P

T

H

(

m

)

O-cell

0

5

10

15

20

25

0 5 10 15 20LOAD (MN)

D

E

P

T

H

(

m

)

= 0.75

= 0.35

139139

0

5

10

15

20

25

0 5 10 15 20LOAD (MN)

D

E

P

T

H

(

m

)

= 0.75

= 0.35

= 0.65

After consideration of potential presence of residual load and applying judgment

Load Distribution

140140

0

5

10

15

20

25

0 5 10 15 20LOAD (MN)

D

E

P

T

H

(

m

)

Schmertmann

E-F

LCPC withoutmax. limitsTEST

LCPC withmax. limits

Load Measured Distribution Compared to Distributions Calculated from the CPTU Soundings

141141

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

0 20 40 60 80 100 120

MOVEMENT (mm)

L

O

A

D

(

K

N

)

Loadtest's Curvefor the Pile Head

Pile Head

Pile Shaft

Pile Toe

Test range

The Test Data for Shaft and Toe and Evaluation of Head-down Movement Using t-z and q-z evaluations

142142

#8

#7

#6

#5

#4#3

#2

#1

121 m

EXAMPLE 13

O-cell Tests on a 2.5 m diameter, 121 m deep bored pile for the Sutong Bridge Project - Jiangsu Province, China, constructed in compact to dense to very dense sand.

Note, two-level O-cell test

143143

TEST RESULTS

Lower O-cell, Stages 1 and 2

-130-120-110-100-90-80-70-60-50-40-30-20-10

01020

0 5 10 15 20 25 30LOAD (MN)

M

O

V

E

M

E

N

T

(

m

m

)

Repeated test after grouting the pile toe

Upper O-cell, Stage 3

-20

0

20

40

60

80

100

120

0 10 20 30 40LOAD (MN)

M

O

V

E

M

E

N

T

(

m

m

)

Upper O-cellPile Head

144

Zambezi River Bridge, Caia, Mozambique

1.5 m diameter60 m embedment

Bored Pile

EXAMPLE 14

145-40

-30

-20

-10

0

10

20

30

0 1 2 3 4 5 6 7 8 9 10 11 12

LOAD (MN)

M

O

V

E

M

E

N

T

(

m

m

)

O-cell Down

O-cell Up

CLAY

SAND

SANDSTONE

SAND

Test Results

146

y = 0.0228x + 0.4653R2 = 0.9995

y = 0.031x + 2.6804R2 = 0.9984y = 0.0352x + 3.9114

0

1

2

3

4

5

6

7

0 50 100 150 200 250 300 350STRAIN ()

S

T

R

E

S

S

(

K

P

a

)

GL-1GL-2

GL-3

y = -0.0173x + 25.553R2 = 0.6372

0

20

40

60

80

0 50 100 150 200 250 300AVERAGE STRAIN ()

T

A

N

G

E

N

T

M

O

D

U

L

U

S

,

M

t

(

G

P

a

)

GL-1

GL-2

GL-3

E-Modulus

Tangent Modulus

147

0

10

20

30

40

50

60

70

0 5 10 15 20 25LOAD (MN)

D

E

P

T

H

(

m

)

Effective stress fitted to data with =0.20 to 0.10

Constant unit shaft resistanceequal to 42 KPa

Load Distribution

148148

The O-Cell test with a couple of strain gages, judiciously placed, will provide:

1. Separate values of shaft and toe resistances

2. Estimate of residual load

3. Load-transfer for the pile

4. Pile-toe load-movement curves (q-z function)

5. Results that can be extrapolated to other piles

6. Data necessary for settlement analysis

149149

Not recognizing that test data can be affected by residual load is the reason for delusive concepts such as the Critical Depth.

Closing remarks

It is unfortunate that this fact is still not generally recognized. As should be obvious, this means that poorly thought-through results keep confusing the practice.

The E-modulus is an important factor in the evaluation of the O-cell data that must not be left to chance.

The analysis is not completed before the test data have been processed in an effective stress calculations and the t-z and q-zrelations have been evaluated.

Instrumentation and taking the readings must be planned, executed, and evaluated by persons who are experienced in all the various phases.

150

The Absolute and Ultimate Bi-direction

151151Vaughani Shores, Vanuatu www.DiveVanuatu.org

basics of design of piled foundations-bengt h.fellenius

Documents

h piles

pile capacity

pile groups16

ocell pile

h questions

h lunchscheduleafternoon13

h break14

h registration08