1

Static Loading Test

and Prediction

Outcome

Bengt H. Fellenius

May 9 2015

A Prediction Challenge to All Delegates to the 2nd CFPB, Santa Cruz, Bolivia.

Mario H. Terceros and Bengt H. Fellenius

We have constructed an instrumented pile and performed a static loading test that we intend to add a bit

of spice to the conference. To this end, we challenge everyone to submit a prediction of the test results.

Then, on Friday, we will start the day with a "Brief report on results of the static loading test and

outcome of the low-key prediction". The "Prediction" referred to is yours.

The Pile

The pile, TP1, is a 600 mm diameter, 16.4 m long, bored pile

constructed on April 20 by pushing a 600-mm diameter, OD,

temporary casing into the ground while augering out the core as

the pipe is pushed down taking care not to auger beyond the toe

of the pipe. Once the pipe reached the intended depth and had

been augered out, concrete (cylinder strength 21 MPa) was

poured into the pipe while it was extracted always maintaining

an inside head of concrete. A 14.0 m long reinforcing cage

consisting of six 20-mm reinforcement bars placed in a circle

with an 450-mm outside diameter was then inserted into the pipe.

The cage had been instrumented with three levels of a single

strain-gage pair at depth 1.80, 9.30, and 13.80 m below the top of

the cage (i.e., at the ground surface). A 310 mm high hydraulic

jack was attached to the bottom of the cage to serve as a

bidirectional cell (BDC) in the first phase of the static loading

test. Thus, in the test, the pile would be separated in an upper

14.8 m length and a lower 1.6 m long length. Telltale guide

pipes were attached to the cage so as to measure the opening of

the BDC and movement of the lower end of the BDC.

The static loading test was performed in two phases. Phase 1

was performed on May 7, 2015, and consisted of a bi-directional

test. In the bidirectional test, the BDC pushes the length above

the BDC (the "upper length") upward and the length below (the

"lower length") downward. The load increments were 50-kN,

each with a 10-minute load-holding time. At the maximum load

of 700 kN, the lower length (1.6 m) plunged. No movement

occurred at the pile head and the net BDC opening was 60+ mm.

16.4

m

13.8

m

9.3

m

1.8

m

Strain Gages

Strain Gages

Ground Surface

PILE

StrainGages

BDC

May 9 2015

Phase 2 test was performed on May 8, 2015. It consisted of leaving the BDC open (free-draining) and

performing a head-down test by means of a conventional reaction pile arrangement. The load increments

were 100-kN, each with a 10-minute load-holding time. The prediction event deals with Phase 2 test, only.

F.y.i., a companion pile, TP2, was constructed on the same day 5 m away from TP1. It was tested as a

full-length pile after the tests on TP1. Pile TP2 is not a part of the prediction event.

The Soil--CPTU and SPT diagrams

The bar in the figure represents the N-indices and the bl/0.3m scale is numerically the same as the qt cone

stress, MPa. The SPT was performed with a constant height-of-fall. The soil profile consists of 9 m thick

layer of silty fine sand, followed by 6 m of fine sand on sand. A 0.2 m thick clay layer was encountered

at 15.0 m depth. The groundwater table is located at 5.0 m depth. The saturated solid densities of the

three soil layers are 2,100, 2,000, 2,100 kg/m3, respectively.

The Prediction Submission

The primary submission is a prediction of the load-movement of the pile shaft (Phase 2) and the capacity

of the shaft, as determined from that same load-movement curve. Submit the values in table showing two

columns, one for load (kN) and one for movement (mm). Use at least 8 load-movement points on the

curve to the maximum load. Give the evaluated capacity as a separate value. You can use either a Word

document or an Excel file. Please submit your prediction to Bengt by e-mail to address:

Bengt@Fellenius.net. The submission deadline is noon May 14.

0

5

10

15

20

25

0 10 20 30 40

DE

PT

H (

m)

Cone Stress, qt (MPa)

0

5

10

15

20

25

0 100 200 300 400

DE

PT

H (

m)

Sleeve Friction, fs (kPa)

0

5

10

15

20

25

0 100 200 300 400

DE

PT

H (

m)

Pore Pressure (kPa)

0

5

10

15

20

25

0 1 2 3 4

DE

PT

H (

m)

Friction Ratio, fR (%)

2

3

Soil Profile

0

5

10

15

20

25

0 10 20 30 40

DE

PT

H (m

)

Cone Stress, qt (MPa)

0

5

10

15

20

25

0 100 200 300 400

DE

PT

H (m

)

Sleeve Friction, fs (kPa)

0

5

10

15

20

25

0 100 200 300 400

DE

PT

H (m

)

Pore Pressure (kPa)

0

5

10

15

20

25

0 1 2 3 4

DE

PT

H (m

)

Friction Ratio, fR (%)

SPT

4

5

“BDC” = Bidirectional Cell; a sacrificial

hydraulic jack

16.4

m

13.8

m

9.3

m

1.8

m

Strain Gages

Strain Gages

Ground Surface

PILE

StrainGages

BDC andtelltales

6

Test Programme

Phase 1 Activate the BDC to perform a bidirectional test, pushing the

upper length upward and the lower length downward. This will

create an opening between the two pile lengths.

Phase 2 Activate the jack on the pile head to perform a head-down test

on the upper pile length with the BDC free-draining The pile will

then function in shaft-bearing only with no toe resistance until

the BDC opening is closed).

Phase 3 If the full resistance of the lower length was not engaged in

Phase 1, then , the jack at the pile head will be closed and the

BDC be re-engaged (The jack at the pile head will now provide

the additional resistance needed).

7

Test Results

Phase 1

The bidirectional (BDC) test pushed the lower length

downward a distance of abut 60 mm at the 700-kN

maximum load---plunging type response. The

measurement is approximate, only, due to friction of the

telltales in the guide pipes. The pile head showed no

movement. Upward movement at the BDC level was

small representing the pile shortening for the load.

8

0

1,000

2,000

3,000

4,000

5,000

6,000

0 10 20 30 40 50 60 70

LO

AD

(k

N)

MOVEMENT (mm)

My Prediction

Predictions

0

1,000

2,000

3,000

4,000

5,000

6,000

0 10 20 30 40 50 60 70

LO

AD

(k

N)

MOVEMENT (mm)

All Predictions Received

0

1,000

2,000

3,000

4,000

5,000

6,000

0 10 20 30 40 50 60 70

LO

AD

(k

N)

MOVEMENT (mm)

All Predictions Received with Capacity Interpretations

The circles are the capacities as interpreted from each curve by the particular predictor

Dashed curve is my prediction prepared with full benefit of the results

of the 2013 tests on similar piles in very similar soil—hardly Class A .

9

0

1,000

2,000

3,000

4,000

5,000

6,000

0 10 20 30 40 50 60 70

LO

AD

(k

N)

MOVEMENT (mm)

with Measured Load-Movement

0

500

1,000

1,500

2,000

2,500

3,000

3,500

0 5 10 15 20 25 30 35

LO

AD

(k

N)

MOVEMENT (mm)

Enlarged View of Predictions and Head-down Test on TP1 Upper Length

10

11

rs = βσ'zz

Movement =

function of E-modulus

rs = f(movement)

The pile is

assumed made

up of a series of

short elements,

each affected by

soil resistance

?WHICH

TO USE

AND

HOW TO

MODIFY

12

The t-z functions actually used for the fit

13

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

0 10 20 30 40 50 60

LO

AD

(k

N)

MOVEMENT (mm)

TP1 Phase 2

Head-down UniPile Simulation of Test

Head-down, Test

Load-Movement for the Upper Pile (14.8 m)

The final fit

14

y = -0.0026x + 6.7169

0

1

2

3

4

5

6

7

8

0 200 400 600 800

SE

CA

NT

ST

IFF

NE

SS

, Q

/μԑ

(GN

)

STRAIN (ԑ)

TP2

Es (GPa) for zero strain = 23.8 GPaEs (GPa) for 700 μԑ = 17.3 GPa

1.7 m

y = -0.0052x + 6.7904

0

1

2

3

4

5

6

7

0 200 400 600 800

TA

NG

EN

T S

TIF

FN

ES

S,

ΔQ

/Δμ

ԑ

(GN

)

STRAIN (ԑ)

TP2

Es (GPa) for zero strain = 24.0 GPaEs (GPa) for 700 μԑ = 17.6 GPa

1.7 m

The Pile Stiffness (EA) Evaluated from the Uppermost Strain-Gage

Unfortunately, the other strain-gages either did not

survive the construction or survived, but were

dislocated--–No usable strain-gage data were obtained

15

Now the results of Phase 1, the bidirectional test

The downward movements are unfortunately

impaired due to friction along the telltales

0

500

1,000

1,500

2,000

0 10 20 30 40 50 60

LO

AD

(k

N)

MOVEMENT (mm)

TP1

Bidirectional Downward

0

500

1,000

1,500

2,000

0 10 20 30 40 50 60

LO

AD

(k

N)

MOVEMENT (mm)

TP1

Bidirectional Downward

16

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

0 10 20 30 40 50 60

LO

AD

(k

N)

MOVEMENT (mm)

TP1

Bidirectional Downward

Head-down, Test

The blue curve is the probable load-movement

curve for the lower length; “Downward”

Phases 1 and 2 together

17

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

0 10 20 30 40 50 60

LO

AD

(k

N)

MOVEMENT (mm)

TP1

Bidirectional Downward

Head-down UniPile Simulation of Test

Head-down, Test

Full Length Head-down UniPile Simulation

Combining the results to the load-movement curve for a head-down test on the full length of pile

18

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

0 10 20 30 40 50 60

LO

AD

(k

N)

MOVEMENT (mm)

TP2

TP1Compression

Head

Toe

UniPile Simulation

Measured

The load-movement curves for the head-down test on Pile 2 with a fit (UniPile) to the data

and a comparison to same for Pile 1.

19

0

2

4

6

8

10

12

14

16

18

0 1,000 2,000 3,000 4,000D

EP

TH

(m

)

LOAD (kN)

Load Distribution, TP2

From fit to Load-

Movement Curve

at 5mm element CPTU E-F

SPT Decourt

Load distributions at the ≈5-mm

element movements for Phase 2

(TP1) combined with the

distribution from CPTU and SPT

analysis of shaft resistance

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

0 10 20 30 40 50 60

LO

AD

(k

N)

MOVEMENT (mm)

TP2

TP1Compression

Head

Toe

UniPile Simulation

Measured

Thank You