mechanical behavior of piled-raft foundation for high ...cem.uaf.edu/media/138828/linlin-gu.pdf ·...

ISSAEST, Fairbanks, AK, USA, August 2-5, 2015

Mechanical behavior of piled-raft foundation

for high-speed railway subjected to train

loading

Linlin Gu, Ph.D. stdnt., Geotechnical Engineering

Nagoya Institute of Technology

Guanlin Ye, Ph.D., Geotechnical Engineering

Shanghai Jiaotong University

Xiaohua Bao, Ph.D., Geotechnical Engineering

Shenzhen University

Feng Zhang, Ph.D., Geotechnical Engineering

Tongji University

August 5, 2015


Outline

Introduction

Description of the case history

Constitutive model for soils and foundation

Numerical simulation

Results and discussion on settlement and

EPWP of subgrade ground

Results and discussion on response of piles

Conclusion

2


Introduction

3

• High-speed railways (speed: 300km/h) are being constructed intensively in Yangtze

River Delta.

• The subgrade soils of the railways are mostly the so-called Shanghai soils with large

water content, high compressibility and low shear strength.

• After the operation of the trains, the ground may settle significantly when subjected to

cyclic train loading if it were not properly designed and constructed.

How to effectively control the settlement of the foundation of the high-speed railway

“Empirical methods” with fitting formula or numerical simulation based on some

primitive constitutive models were used to calculate the ground settlement and

change of EPWP during and after the train vibration. Unfortunately, were not

accurate enough and above all, lack of rationality.

Traditional methods…

EPWP: Excess pore water pressure


Introduction

4

This research …

Numerical simulation based on

Cyclic Mobility Model (Zhang et

al.2007, 2011)

describe properly the soils subjected to

different loadings, dynamic or static, under

different drained conditions in a unified way

investigate

Behavior of piled-raft foundation during

the train loading but also in post-loading

consolidation (simulation result)

Monitoring data within

one month

compare

Performance of this numerical simulation

(the changes of settlement and EPWP)

demonstrate

ISSAEST, Fairbanks, AK, USA, August 2-5, 2015 5


60

13.2

06.8

08.2

28.7

312.4

15.7

74.0

3

6.0

0

58.1

14.8

23.6

0

F

12

A3 C3B3

A2 B2 C2

A1 B1 C1

1

2

3

4

5

6

7

8

9

10

A1 B1 C1

A2 B2 C2

A3 C3B3

Ⅰ Ⅱ Ⅲ

Artificial fillClayey soil

Silty clay

Mucky soil

Silty clay

Mucky soil

Silty clay

Silty clay

Silty clay

Silty sand

Survey points



Piled-raft foundation

Plane view Sectional view



60

13.2

06.8

08.2

28.7

31

2.4

15.7

74.0

3

6.0

0

58

.1

14.8

23.6

0

F

12

A3 C3B3

A2 B2 C2

A1 B1 C1

1

2

3

4

5

6

7

8

9

10

A1 B1 C1

A2 B2 C2

A3 C3B3

Ⅰ Ⅱ Ⅲ

Artificial fillClayey soil

Silty clay

Mucky soil

Silty clay

Mucky soil

Silty clay

Silty clay

Silty clay

Silty sand

a thickness of 2-3m,

crusty layer

high plasticity, the softest

stratum, a sensitivity of

about 4.5-5.5

less sensitivity (about 3-

3.5)

dense fine sandy layer,

the supporting layer of

the pile

Shanghai Soil

Horizontal distributed Grain size distribution

Undisturbed samples from No-2 and No-9 layers sampled using a

Shelby thin-walled tube sampler.

Undisturbed samples from No-4 layer at the depth of 10m were taken

with block sampling method.


Constitutive model for Shanghai soils

8

A kinematic hardening elastoplastic model using an associated flow rule, initially

proposed by Zhang et al. (2007, 2011)

Describe the mechanical behavior of a soil with different density, subjected to

different loading (monotonic or cyclic) under different drained condition, in a

unified way by considering the effects of stress-induced anisotropy, density, and the

structure formed during the natural deposition process.

Cyclic Mobility Model

-60

-40

-20

0

20

40

60 -0.1

-0.05

0

0.05

0.10 0.1 0.2 0.3 0.4

q-simulationq-test

v-simulation

v-test

Volu

metric

strain

v

Devia

tor

stre

ss q

(kP

a)

Shear strain s

-200

-100

0

100

200 -0.06

-0.03

0

0.03

0.060 0.03 0.06 0.09 0.12

q-simulationq-test

v-simulation

v-test

Shear strain s

Volu

metric strain

v

Dev

iato

r st

ress

q (

kP

a)

-1500

-1000

-500

0

500

1000

1500 -0.03

-0.02

-0.01

0

0.01

0.02

0.030 0.05 0.1 0.15 0.2 0.25

q-simulationq-test

v-simulation

v-test

Shear strain s

Volu

metric strain

v

Dev

iato

r st

ress

q (

kP

a)

Clayey soil (No-2 layer) Clayey soil (No-4 layer) Sandy soil (No-9 layer)

Test: Drained monotonic triaxial test

Verify


Constitutive model for piled-raft foundation

9

Parameters piles Raft

Young’s modulus E (kPa) 3.25×107 3.25×107

Cross sectional area A (m2) 0.0784 -

Inertia moment I (m4) 1.23×10-3 -

Density ρ(t/m3) 2.42 2.42

Poisson’s ratio ν 0.200 0.200

Material parameters of piles and raft

Read-made

concrete

Raft is described by isoparametric solid elements with a linear elasticity.

Pile is modeled with beam element, described by a trilinear model

considering the hysteresis effect of cyclic loading, the first, second and

ultimate yielding moments of the pile, Mc, My and Mu are 150, 190 and 200

kN·m, respectively.



10

Code: DBLEAVES (Ye, 2007; Ye, 2011; Jin et al. 2010; Xia et al. 2010; Bao et al.

2012; Morikawa et al. 2011)

drainage boundary200 m 200 m30 m 30 m

imp

erv

iou

s

imp

ervio

us

equal displacement condition equal displacement condition

Node:1113

Element:1040

train

impervious

FEM mesh used in the numerical calculation

CRH2 type with a speed of 300 km/h,

length is 201.4m



11

Excitation force F is expressed with a function superimposed by a

series of sine functions. (Liang et al. 1999)

Duration: 2.42s

Maximum value: 97.6 kN (compression)

-100

-80

-60

-40

-20

0

0 0.5 1 1.5 2 2.5

t (sec)

Exci

tati

on f

orc

e F

(kN

)



12

Scenario of the calculation in one day

Calculating stage number

1 2 3 4 5 6 7 8 9 10

The type of loading D C D C D C D C D C

Duration time at one

stage (sec) 2.42 5400. 2.42 5400. 2.42 5400. 2.42 5400. 2.42 5400.

Time interval of each

integration step (sec) 0.01 1.0 0.01 1.0 0.01 1.0 0.01 1.0 0.01 1.0

Integration steps 24200 5400 24200 5400 24200 5400 24200 5400 24200 5400

Calculating stage number

11 12 13 14 15 16 17 18 19 20

The type of loading D C D C D C D C D C

Duration time at one

stage (sec) 2.42 5400. 2.42 5400. 2.42 5400. 2.42 5400. 2.42 37776.

Time interval of each

integration step (sec) 0.01 1.0 0.01 1.0 0.01 1.0 0.01 1.0 0.01 1.0

Integration steps 24200 5400 24200 5400 24200 5400 24200 5400 24200 37776

dynamic loading = D

consolidation = C



13

Parameter 1 2 3 4 5 6 7 8 9 10

Compression index λ 0.235 0.0600 0.132 0.140 0.135 0.135 0.130 0.130 0.0500 0.130

Swelling index κ 0.066 0.0050 0.066 0.066 0.066 0.0064 0.066 0.064 0.012 0.066

Stress ratio at critical state Μ

1.20 1.20 1.30 1.30 1.40 1.40 1.18 1.30 1.45 1.24

Void ratio N (p’=98 kPa on N.C.L.) 0.94 0.68 1.0 0.86 0.84 0.86 0.70 0.79 0.69 0.86

Poisson’s ratio ν 0.35 0.32 0.38 0.38 0.35 0.35 0.35 0.28 0.25 0.28

Parameter of overconsolidation m 2.0 1.0 4.0 5.0 1.5 1.5 1.5 1.2 0.020 1.5

Parameter of structure a 0.010 0.010 0.10 0.10 0.10 0.10 0.10 0.050 1.5 0.10

Parameter of anisotropy br

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.5 0.00

Material parameters of soils

Initial values of state variables of soils Parameter 1 2 3 4 5 6 7 8 9 10

Void ratio e0 1.10 0.757 1.08 0.860 0.815 0.825 0.630 0.750 0.650 0.800

Mean effective stress

p’(kPa) 20.9 32.7 59.9 98.8 111 190 242 249 284 355

Degree of structure R0* 0.50 0.70 0.30 0.20 0.60 0.60 0.80 0.80 0.80 0.60

Overconsolidation OCR

(1/R0) 1.00 6.50 1.20 1.20 1.25 1.20 3.00 2.00 10.0 1.20

Anisotropy ζ0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00



14

Element behavior of soils

-6

-3

0

3

6

0 5 10 15 20 25

Effective stress p' (kPa)

Dev

iato

r st

ress

q (

kP

a)

No 2 layer

-15

-10

-5

0

5

10

15

30 45 60 75 90


Dev

iato

r st

ress

q (

kP

a)

No 4 layer

-100

-50

0

50

100

0 100 200 300 400 500 600


Dev

iato

r st

ress

q (

kP

a)

No 9 layer

Effective stress path

-6

-3

0

3

6

-0.1 -0.05 0 0.05 0.1

Shear strain s

Dev

iato

r st

ress

q (

kP

a)

No 2 layer-15

-10

-5

0

5

10

15

-0.02 -0.01 0 0.01 0.02

Shear strain s

Dev

iato

r st

ress

q (

kP

a)

No 4 layer

-100

-50

0

50

100

-0.02 -0.01 0 0.01 0.02

Shear strain s

Dev

iato

r st

ress

q (

kP

a)

No 9 layer

Stress-strain relations



15

-0.1

-0.08

-0.06

-0.04

-0.02

0

0 10 20 30 40

SimulationSurvey

t (d)

Set

tlem

ent

(m)

A1

-0.1

-0.08

-0.06

-0.04

-0.02

0

0 10 20 30 40

SimulationSurvey

t (d)S

ettl

emen

t (m

)

B1

-0.1

-0.08

-0.06

-0.04

-0.02

0

0 10 20 30 40

SimulationSurvey

t (d)

Sett

lem

en

t (m

)

C1

0.057

0.040

0.089

0.052

0.087

0.050

largest settlement

Excitation force in calculation is assigned to be the commuter trains passing at the

same time，while，it is rare that two trains in different directions passed through the

monitoring section at the same time.

Changes in settlements at prescribed points within one month



16

-0.1

-0.08

-0.06

-0.04

-0.02

0

0 10 20 30 40

t (d)

Sett

lem

en

t (m

)

A2

-0.1

-0.08

-0.06

-0.04

-0.02

0

0 10 20 30 40

t (d)

Sett

lem

en

t (m

)

B2

-0.1

-0.08

-0.06

-0.04

-0.02

0

0 10 20 30 40

t (d)

Sett

lem

ent

(m)

C2

0.088 0.089 0.089

-0.1

-0.08

-0.06

-0.04

-0.02

0

0 10 20 30 40

t (d)

Set

tlem

ent

(m)

A3

-0.1

-0.08

-0.06

-0.04

-0.02

0

0 10 20 30 40

t (d)

Set

tlem

ent

(m)

B3

-0.1

-0.08

-0.06

-0.04

-0.02

0

0 10 20 30 40

t (d)

Set

tlem

ent

(m)

C3

0.089 0.089 0.087

Changes in settlements at prescribed points within one month

Settlement: A2≈B2≈C2， A3≈B3≈C3

Relative deformation of the soils within the piles is also very tiny due to the

interaction of the piles and the soils.


Results and discussion on EPWP of subgrade ground

17

-1

0

1

2

3

0 10 20 30 40t (d)

EP

WP

(kP

a)

A1

-1

0

1

2

3

0 10 20 30 40

t (d)

EP

WP

(kP

a)

B1

-1

0

1

2

3

0 10 20 30 40

t (d)

EP

WP

(kP

a)

C1

No-2 layer (clayey soil)

Changes in EPWP within one month

Turned negative

A cyclic process of growth and dissipation, but mainly in zero level.

Even if the raft has a much larger stiffness than those of piles, the

responses at different places may be quite different.

Soil beneath the loading point (C1) should settle more severely than the

other places, however, due to the condition that the soil and the raft are

connected, the soil could not settle, resulting in a negative EPWP.



18

No-6 layer (mucky soil)


-2

0

2

4

6

8

10

0 10 20 30 40

t (d)

EP

WP

(kP

a)

A2

-2

0

2

4

6

8

10

0 10 20 30 40

t (d)E

PW

P (

kP

a)

B2

-2

0

2

4

6

8

10

0 10 20 30 40

t (d)

EP

WP

(kP

a)

C2

up

No-9 layer (silty fine-grained sand)


-0.5

0

0.5

1

1.5

2

2.5

0 10 20 30 40t (d)

EP

WP

(kP

a)

A3

-0.5

0

0.5

1

1.5

2

2.5

0 10 20 30 40

t (d)

EP

WP

(kP

a)

B3

-0.5

0

0.5

1

1.5

2

2.5

0 10 20 30 40

t (d)

EP

WP

(kP

a)

C3

Poor

drainage

capacity

Limited drainage

ability during the

vibration, EPWP

accumulated easily,

but it could dissipate

completely after a

period time.



3.75 kPa 6.50 kPa 9.60 kPa

EPWP distribution at different times (Unit=kPa)

EPWP mainly concentrated in the two sides of group pile within No-4,

No-5 and No-6 layers, so the soils within the group piles were less

deformed.

(10 days) (20 days) (30 days)



Length of the pile l=39.35m, diameter D=0.5m, frictional pile

0

30

60

90

120

0 10 20 30 40

Pile 1

tipmiddlehead

Ax

ial

stre

ss (

kN

)

t (d)

-40

0

40

80

120

0 10 20 30 40

Pile 2

tipmiddlehead

t (d)

Ax

ial

stre

ss (

kN

)

-80

-40

0

40

80

0 10 20 30 40

Pile 3

tipmiddlehead

t (d)

Axia

l st

ress

(kN

)

Changes of axial stress of the piles within one month

upward downward transition

Relative movement to soil:

EPWP at C1 (right beneath the loading point) vibrated mostly and negative EPWP

occurred, resulting in tensile axial force at the head of pile 3.

For pile 2, the axial forces at the head and the middle part were almost equal to

zero, taking an even value of pile 1 and pile 3.

At pile tip, the values of the compressive axial forces of the piles were in the

order of pile 1, 2 and 3.



-40

-30

-20

-10

0

-20 -10 0 10 20 30

Pile 1Pile 2Pile 3

Bending moment (kN·m)

Dep

th o

f th

e pil

es (

m)

-40

-30

-20

-10

0

-20 -10 0 10 20 30

Pile 1Pile 2Pile 3

Shear force (kN)D

epth

of

the

pil

es (

m)

-40

-30

-20

-10

0

-100 0 100 200 300

Pile 1Pile 2Pile 3

Axial force (kN)

Dep

th o

f th

e pil

es (

m)

Free end

symmetrically central line

Increase dramatically

Pile 1> Pile 2

Uneven settlement of the soils due to the interaction between the piles

and the soils resulted in relative large bending moment.

Change of shear force followed the change of bending moment.

Distribution of sectional forces after one-month trial operation


Conclusion

1. High-speed railway is constructed in Shanghai soils, a

very soft diluvial ground, considerable settlement and

EPWP happened due to the cyclic train loading. Both

field observation and calculation give the same

tendency.

2. In the calculation, the mechanical behavior of the

foundation and surround soils is considered not only

during the train loading but also in post-loading

consolidation. The calculation is conducted with a

series of dynamic/static analyses in unified sequential

way strictly coincident with the field history.


Conclusion

3. The accuracy of the calculation is assured with the

fact that the FE-FD analysis is based on a

constitutive model that can describe properly the soils

subjected to different loadings, dynamic or static,

under different drained conditions in a unified way.

4. The mechanical behaviors of the piled-raft and the

soils, e.g., the accumulation of settlement and EPWP,

the distributions of EPWP, the sectional forces of

piles, are on the whole well described by the

calculation.

mechanical behavior of piled-raft foundation for high ...cem.uaf.edu/media/138828/linlin-gu.pdf ·...

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