group of geotechnical engineering university of cantabria ...university of cantabria, santander,...

University of Cantabria, Santander, Spain

Pore pressures during stone column installation

18 EYGEC, 17-20 June 2007, Ancona, Italy

Jorge Castro Group of Geotechnical Engineering


http://centros.unican.es/caminos


Outline

Introduction

Site characterization

Instrumentation

Data analysisPeaks of pore pressures

Influence of previous column installations

Pore pressure dissipation

Conclusions

Introduction ●


●

Instrumentation ●

Data analysis

●

Conclusions 2/16



Introduction

●


●

Instrumentation ●

Data analysis

●

Conclusions


Introduction

3/16



Introduction ●

Site characterization ●

Instrumentation ●

Data analysis

●

Conclusions




CPTU

BoreholeDepth(m)

γd

(kN/m3)W(%)

wL(%)

wP(%)

Between columns

4-4.6 17.0 21 35.4 19.5

8-8.6 17.2 22 34.2 16.8

10.1-10.7 16.4 22 32.2 16.3

Outside columns

2-2.6 17.8 18 21.8 16.7

4-4.6 17.0 22 33.0 18.3

6-6.6 17.4 19 33.6 18.1

8.6-9.2 17.3 21 26.6 8.4

Summary of index soil tests

4/16


Introduction ●


Instrumentation ●

Data analysis

●

Conclusions




Borehole Depth(m) c'(kPa) Φ(º) cu

(kPa) cc cs

Between columns

4-4.6 25 26 29.5 0.130 0.020

8-8.6 20 25 30.5 0.110 0.017

10.1-10.7 15 28 0.109 0.012

Outside columns

2-2.6 70 32 0.086 0.008

4-4.6 23 29 78.0 0.123 0.016

6-6.6 31 26 166.5 0.118 0.012

8.6-9.2 30 30 57.0 0.065 0.006

Summary of oedometer, triaxial and unconfined compression tests

5/16

Cv

≈

10-3/10-4

cm2/s


Introduction ●


Instrumentation ●

Data analysis

●

Conclusions




Column properties

Triangular pattern

Dry bottom-feed method

Diameter dc = 0.8 m

Spacing de = 2.8 m

Area replacement ratio

ar

=0.074

Length L = 9 m

6/16


Introduction ●


●

Instrumentation

●

Data analysis

●

Conclusions


Instrumentation


ROADSUECA

PZ01_1-PZ01_2

PZ02_1-PZ02_2

PZ03_1-PZ03_2

4 m

7 m6,60 m

PZ01_1

PZ01_2

PZ02_1

PZ02_2

PZ03_1

PZ03_2

STONE COLUMN

5

7

6

4

3

2

1

7/16


Introduction ●


●

Instrumentation

●

Data analysis

●

Conclusions


Instrumentation


02468

1016:00:00 16:30:00 17:00:00.0 17:30:00 18:00:00 18:30:00

Dep

th (m

)

050

100150200

16:00:00 16:30:00 17:00:00.0 17:30:00 18:00:00 18:30:00

Time

Cur

rent

(am

pere

)

0

20

40

60

80

100

120

140

160

16:00:00 16:30:00 17:00:00.0 17:30:00 18:00:00 18:30:00

PZ 01PZ 02PZ 03

Por

e pr

essu

re m

easu

red

(kP

a)

8/16


0

10

20

30

0 1.5 3.0 4.5

4m7m

CO

LUM

N

k=22.2 kPaR=5.37m

k=22.8 kPaR=5.63 m

Distance to SC 1 (m)

Pea

k of

por

e pr

essu

re (k

Pa)

Introduction ●


●

Instrumentation ●

Data analysis

●

Conclusions


Data analysis

9/16


⎟⎠⎞

⎜⎝⎛=Δ

rRku ln

First

column

installation

Elastic-perfectly

plastic

behaviour

uck 2=


Introduction ●


●

Instrumentation ●

Data analysis

●

Conclusions


Data analysis


10/16

0

25

50

75

100

0 1.5 3.0 4.5

4m7m

CO

LUM

N

k=34.4 kPaR=4.89 kPa

k=73.4 kPaR=4.51 m

Distance to the column (m)

Pea

k of

por

e pr

essu

re (k

Pa) ⎟

⎠⎞

⎜⎝⎛=Δ

rRku ln

Elastic-perfectly

plastic

behaviour

uck 2=

All

column

installations


Introduction ●


●

Instrumentation ●

Data analysis

●

Conclusions


Data analysis


0

20

40

60

80

100

0 10 20 30 40 50

PZ 01PZ 02PZ 03

Peak of pore pressure at 4m (kPa)

Pea

k of

por

e pr

essu

re a

t 7m

(kP

a)

11/16


Introduction ●


●

Instrumentation ●

Data analysis

●

Conclusions


Data analysis


1

2

3

4

5

1 2 3 4 5

PZ 01PZ 02PZ 03

u/u0 (4m)

u/u 0 (7

m)

12/16


Introduction ●


●

Instrumentation ●

Data analysis

●

Conclusions


Data analysis


0

10

20

30

40

50

1.5 2.5 3.5 4.5

4

3

5

2

1

Distance to column (m)

Pea

k of

por

e pr

essu

re (k

Pa)

PZ01-1

0

10

20

30

40

50

1.5 2.5 3.5 4.5

6

3

4

5

2

1


Pea

k of

por

e pr

essu

re (k

Pa)

PZ01-2

0

10

20

30

40

50

60

70

80

90

100

1.5 2.5 3.5 4.5

7

6

3

4

5

21


Pea

k of

por

e pr

essu

re (k

Pa)

PZ02-2

0

10

20

30

40

50

60

70

80

90

100

1.5 2.5 3.5 4.5

6

3

4

5

2

1


Pea

k of

por

e pr

essu

re (k

Pa)

PZ02-1

13/16


Introduction ●


●

Instrumentation ●

Data analysis

●

Conclusions


Data analysis


0

20

40

60

80

00:00:00 00:03:00 00:06:00 00:09:00 00:12:00 00:15:00

PZ03-1 / SC 2PZ03-1 / SC 3PZ02-1 / SC 5

Time (hh:mm:ss)

Exc

ess

pore

pre

ssur

es (k

Pa)

14/16


Introduction ●


●

Instrumentation ●

Data analysis

●

Conclusions


Data analysis

15/16


0

20

40

60

80

100

0 5 10 15 20

No fractured zonerf=2arf=3a

Time (days)

Exc

ess

pore

pre

ssur

es (k

Pa)

0

50

100

150

200

250

0 2 4 6

10 days1 day0.1 dayu0

CO

LUM

N

r (m)

Exc

ess

pore

pre

ssur

es (k

Pa)

Isochrones without fractured zone Consolidation curves at piezometer (r=1.6 m)

Ch

=10-2

cm2/s


Introduction ●


●

Instrumentation ●

Data analysis

●

Conclusions


Conclusions

16/16


Results of field instrumentation to study pore pressures during

stone column installation

Peaks of pore pressures fairly well matched by cavity

expansion theory

Depth influence

Previous column installation influence

Difficult to explain the fast dissipation


group of geotechnical engineering university of cantabria ...university of cantabria, santander,...

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