Liquefaction-Induced Lateral Spreading and its Effects on Pile Foundations

Liangcai He

Committee in Charge:

Professor Ahmed Elgamal, Chair

Professor Scott Ashford

Professor J. Enrique Luco

Professor Jean-Bernard Minster

Professor Hidenori Murakami

Department of Structural Engineering

University of California, San Diego UCSD

One-g Shake Table Experiments

Laminar Soil Box

Laminar Soil Box

Rigid Soil Box

UCSD Shake Table Experiment with a Rigid Soil Box (1)

UCSD Shake Table Experiment with a Rigid Soil Box (2)

UCSD Shake Table Experiment with a Rigid Soil Box (3)

Time (s)

Model Shaking

189

A1

A2

A3

A4

A5

D1

TA

D12

D2

D3

D5

D6

D7

D8

D9

TD

D4

D13

D10 D11

20

20

20

20

20

20

20

20

2919

Displacement PotPore-Pressure SensorUnit: cm Accelerometer

Silica Sand(Dr=40%)

2o

170

35

A15

A6

A7

A8

A9

A10

A11

A12

A13

A14

PWP1

PWP2

PWP3

PWP4

10

20

40

40

40

39

A21A22

A23

A24

PWP7

PWP9

PWP10

PWP12

A26

A27

A28

A29

A16A17

A18

A19

PWP5

PWP6

PWP11

A25A30A20

PWP8

Three Shake Table Experiments with a Laminar Box

Experiment Model Preparation

Time (s)

Model Shaking – Top View

Model Shaking – Side View

UCSD-Japan Joint Research

6m high, 0.3m diameter Pile, Shake Table Tests

Whole soil layer is liquefiableUnliquefiable crust over liquefiable layer

Pile moment Free field excess pore pressure

Model Response During Shake Table Experiments

Free field acceleration Free field displacement

Model Response During Shake Table Experiments

Excess pore pressure downslope the stiff pile Excess pore pressure upslope the stiff pile

Model Response During Shake Table Experiments

Model Response During Shake Table Experiments

Model Response Summary1. Conducted one-g shake table experiments show excellent

repeatability in terms of pore pressure, acceleration, displacement, and pile responses. Shaking successfully liquefied the soil and induced lateral spreading.

2. Free field excess pore pressure reached initial effective stress at the first few cycles of shaking, indicating soil liquefied relatively early.

3. Pore pressures at the downslope side of piles showed larger dips due to the fact that soil moved more than the pile.

4. No strong dilation in the soil was observed during the experiments.

5. After liquefaction, soil accelerations near ground surface decreased significantly and ground displacement kept increasing as shaking continued.

6. Pile response gradually increased before soil liquefaction. After liquefaction, the soil failed against the pile and started to flow around the pile. As a result, pile response gradually decreased.

Maximum Moment and Pressure Profiles

Top view of Test Setup

Back-Calculated Maximum Uniform Soil Pressure

Test

Maximum pile response

Free field ground surface displacement

Soil pressure(kPa)

PileMmax

(kN·m)

Pile head deflection

(cm)

At the same time as Mmax

(cm)

At end of shaking

(cm)

Rigid1Left pile 0.63 N/A N/A N/A 5.5

Right pile 0.64 N/A N/A N/A 5.5

Rigid2Front pile 1.4 N/A N/A N/A 11.0

Trailing pile 0.53 N/A N/A N/A 4.5

Rigid3 Single pile 1.86 1.4 N/A N/A 11.5

UCSD1 Single pile 2.65 4.2 8.5 12.5 7

UCSD2 Single pile 3.00 1.6 2.8 7.8 6

UCSD3 Single pile 2.83 1.2 1.9 2.5 7

Japan1 Stiff pile 86 10 7 27 22

Japan2 Stiff pile 118 12 8 15 25

Japan3

Stiff pile 166 14 19

52

40

Flexible pile 183 25 43 40

Japan4

Stiff pile 132 11 13

105

40

Flexible pile 95 21 15 40

Liquefied SoilLateral Spreadingz

Ground Surface

PileDobry et al.

(2003)This study shows passive

failure of uphill soil Japan Road Association

(2002)

p=10.3 kPa p=0.3tz p=kptz, kp=tan2(45+/2),

and =3º for liquefied soil

Lateral spreading pressure on piles

Rotational stiffness Kr was

measured before shaking

Comparison of Various Methods

3D Finite Element Study

OpenSees

Software Package

Solid Node Fluid Node

Beam Element for Pile

Solid-Fluid Fully Coupled Element for Soil

Conical yield surface in principle stress space and deviatoric plane

Shear stress, effective confinement, and shear strain relationship

Soil Constitutive Model

Ground Response - Acceleration

Ground Response - Displacement

Ground Response – Pore Pressure

Pile Response – Displacement

Pile Response – Moment

M

κ

Numerical

Actual

Deformed Mesh at 10 seconds

Pore pressure at 10 s

Pile Reinforcement Effect

Conclusions

Horizontal ground motions dominate lateral spreading. The influence of vertical motion on lateral spreading is very small.

Pile group and shadowing effects can reduce lateral load on individual piles by about 50%

Experimental and case history observations show soil failed passively against the pile.

A passive pressure method based on liquefied strength of the soil is proposed to estimate pile response to lateral spreading. This method satisfactorily predicted pile response in all shake table experiments as well as the performance of piles during past earthquakes.

Current design methods can satisfactorily predict the response of short piles in shallow liquefied soil layers but significantly underestimate the response of longer piles in deeper liquefied ground.

The FEM successfully simulated the one of the shake table experiments. It is found that the piles have apparent reinforcement effects on the ground.

Recommendations for Future Research

Additional shake table experiments can be conducted using a large laminar box and a single pile of different sizes and different levels of stiffness to further study pile pinning effects.

It will be very useful to conduct one-g shake table experiments and numerical analysis on the case of a liquefiable ground with a stiff crust .

Pile behavior in liquefiable steep slope might be different from liquefiable infinite mildly inclined slope. One-g shake table experiments and numerical study can be conducted to bring valuable insights into this case.

Thank you !