348 Static Test and Predictions 2nd CFPB

8/18/2019 348 Static Test and Predictions 2nd CFPB

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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 bitof 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 pileconstructed on April 20 by pushing a 600-mm diameter, OD,temporary casing into the ground while augering out the core asthe pipe is pushed down taking care not to auger beyond the toeof the pipe. Once the pipe reached the intended depth and hadbeen augered out, concrete (cylinder strength 21 MPa) waspoured into the pipe while it was extracted always maintainingan inside head of concrete A 14 0 m long reinforcing cage

1 . 8

mStrainGages

Ground Surface

PILE


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May 9 2015

Phase 2 test was performed on May 8, 2015. It consisted of leaving the BDC open (free-draining) andperforming 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., TP2, a companion pile of equal length and size, was constructed on the same day 5 m away fromTP1. 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 q t conestress, MPa. The SPT was performed with a constant height-of-fall. The soil profile consists of 9 m thicklayer of silty fine sand, followed by 6 m of fine sand on sand. A 0.2 m thick clay layer was encounteredat 15.0 m depth. The groundwater table is located at 5.0 m depth. The saturated solid densities of thethree soil layers are 2 100 2 000 2 100 kg/m 3 respectively

0

5

10

15

20

25

0 10 20 30 40

D E P T H ( m )

Cone Stress, q t (MPa)

0

5

10

15

20

25

0 100 200 300 400

D E P T H ( m )

Sleeve Friction, f s (kPa)

0

5

10

15

20

25

0 100 200 300 400

D E P T H ( m )

Pore Pressure (kPa)

0

5

10

15

20

25

0 1 2 3 4

D E P T H ( m )

Friction Ratio, f R (%)


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Soil Profile

0

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25

0 10 20 30 40

D E P T H ( m )

Cone Stress, q t (MPa)

0

5

10

15

20

25

0 100 200 300 400

D E P T H ( m )

Sleeve Friction, fs

(kPa)

0

5

10

15

20

25

0 100 200 300 400

D E P T H ( m )

Pore Pressure (kPa)

0

5

10

15

20

25

0 1 2 3 4

D E P T H ( m )

Friction Ratio, fR

(%)

SPT

4


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“BDC” = Bidirectional Cell; a sacrificialhydraulic jack

1 6

. 4 m

1 3

. 8 m

9 . 3

m

1 . 8

mStrainGages

StrainGages

Ground Surface

PILE

StrainGages

BDC andtelltales


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Test Programme

Phase 1 Activate the BDC to perform a bidirectional test, pushing theupper length upward and the lower length downward. This willcreate an opening between the two pile lengths.

Phase 2 Activate the jack on the pile head to perform a head-down teston the upper pile length with the BDC free-draining The pile willthen function in shaft-bearing only with no toe resistance untilthe BDC opening is closed).

Phase 3 If the full resistance of the lower length was not engaged inPhase 1, then , the jack at the pile head will be closed and theBDC be re-engaged (The jack at the pile head will now providethe additional resistance needed).


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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.


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0

1,000

2,000

3,000

4,000

5,000

6,000

0 10 20 30 40 50 60 70

L O A D ( k N )

MOVEMENT (mm)

My Prediction

Predictions

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6,000

0 10 20 30 40 50 60 70

L O A D ( k N )

MOVEMENT (mm)

All Predictions Received

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0 10 20 30 40 50 60 70

L O A D ( k N )

MOVEMENT (mm)

All Predictions Received with Capacity Interpretations

The circles are the capacities as interpreted

from each curve by the particular predictor


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Dashed curve is my prediction prepared with full benefit of the resultsof the 2013 tests on similar piles in very similar soil — hardly Class A .

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0

1,000

2,000

3,000

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0 10 20 30 40 50 60 70

L O A D ( k N )

MOVEMENT (mm)

with Measured Load-Movement


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0500

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1,500

2,000

2,5003,000

3,500

0 5 10 15 20 25 30 35

L O A D ( k N )

MOVEMENT (mm)

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

10


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rs = βσ 'zz

Movement =function ofE-modulus

rs = f(movement )

The pile isassumed madeup of a series of

short elements,each affected bysoil resistance

?WHICHTO USEANDHOW TOMODIFY

Fitting analysis to the results


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The t-z functions actuallyused for the best fit


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0

500

1,000

1,500

2,000

2,500

3,000

3,5004,000

0 10 20 30 40 50 60

L O A D ( k N )

MOVEMENT (mm)

TP1 Phase 2

Head-downUniPileSimulationof Test

Head-down,Test

Load-Movement for the Upper Pile (14.8 m)

The final fit


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y = -0.0026x + 6.7169

0

1

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3

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7

8

0 200 400 600 800 S E C A N T S T I F F N E S S

, Q / μ ԑ

( G N )

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

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3

4

5

6

7

0 200 400 600 800

T A N G E N T S T I F F N E S S

, Δ Q / Δ μ ԑ

( G N )

STRAIN (ԑ)

TP2

E s (GPa) for zero strain = 24.0 GPaE s (GPa) for 700 μԑ = 17.6 GPa

1.7 m

The Pile Stiffness (EA) Evaluated

from the Uppermost Strain-GageUnfortunately, the other strain-gages either did notsurvive the construction or survived, but weredislocated-- – No usable strain-gage data were obtained


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Now the results of Phase 1, thebidirectional test

The downward movements are unfortunatelyimpaired due to friction along the telltales

0

500

1,000

1,500

2,000

0 10 20 30 40 50 60

L O A D

( k N )

MOVEMENT (mm)

TP1

BidirectionalDownward

0

500

1,000

1,500

2,000

0 10 20 30 40 50 60

L O A D

( k N )

MOVEMENT (mm)

TP1



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0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

0 10 20 30 40 50 60

L O A D ( k N )

MOVEMENT (mm)

TP1


Head-down,Test

The blue curve is the probable load-movementcurve for the lower length; “Downward”

Phases 1 and 2 together


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0500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

0 10 20 30 40 50 60

L O A D ( k N )

MOVEMENT (mm)

TP1


Head-downUniPile

Simulationof TestHead-down,Test

Full Length Head-downUniPile Simulation

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


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0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

0 10 20 30 40 50 60

L O A D ( k N )

MOVEMENT (mm)

TP2

TP1CompressionHead

Toe

UniPile

Simulation

Measured

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

and a comparison to same for Pile 1.


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0

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

D E P T H ( m

)

LOAD (kN)

Load Distribution, TP2

From fit to Load-Movement Curveat 5mm elementCPTU E-F

SPT Decourt

Load distributions at the ≈5-mmelement movements for Phase 2

(TP1) combined with thedistribution from CPTU and SPT

analysis of shaft resistance

0

500

1,000

1,5002,000

2,500

3,000

3,500

4,000

0 10 20 30 40 50 60

L O A D

( k N )

MOVEMENT (mm)

TP2

TP1CompressionHead

Toe

UniPileSimulation

Measured


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hank You

348 Static Test and Predictions 2nd CFPB

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