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Liquefaction-Induced Lateral Spreading and its Effects on Pile Foundations Liangcai He Committee in Charge: Professor Ahmed Elgamal, Chair Professor Scott.

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Presentation on theme: "Liquefaction-Induced Lateral Spreading and its Effects on Pile Foundations Liangcai He Committee in Charge: Professor Ahmed Elgamal, Chair Professor Scott."— Presentation transcript:

1 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

2 One-g Shake Table Experiments Laminar Soil Box Rigid Soil Box

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

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

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

6 Time (s) Model Shaking

7 Three Shake Table Experiments with a Laminar Box

8 Experiment Model Preparation

9 Time (s) Model Shaking – Top View

10 Model Shaking – Side View

11 UCSD-Japan Joint Research

12 6m high, 0.3m diameter Pile, Shake Table Tests Whole soil layer is liquefiableUnliquefiable crust over liquefiable layer

13 Pile momentFree field excess pore pressure Model Response During Shake Table Experiments

14 Free field acceleration Free field displacement Model Response During Shake Table Experiments

15 Excess pore pressure downslope the stiff pileExcess pore pressure upslope the stiff pile Model Response During Shake Table Experiments

16

17 Model Response Summary 1.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.

18 Maximum Moment and Pressure Profiles Top view of Test Setup

19 Back-Calculated Maximum Uniform Soil Pressure Test Maximum pile response Free field ground surface displacement Soil pressure (kPa) Pile M max (kN · m) Pile head deflection (cm) At the same time as M max (cm) At end of shaking (cm) Rigid1 Left pile0.63N/A 5.5 Right pile0.64N/A 5.5 Rigid2 Front pile1.4N/A 11.0 Trailing pile0.53N/A 4.5 Rigid3Single pile N/A 11.5 UCSD1Single pile UCSD2Single pile UCSD3Single pile Japan1Stiff pile Japan2Stiff pile Japan3 Stiff pile Flexible pile Japan4 Stiff pile Flexible pile

20 Liquefied Soil Lateral Spreading z Ground Surface Pile Dobry et al. (2003) This study shows passive failure of uphill soil Japan Road Association (2002) p=10.3 kPa p=0.3  t z p=k p  t z, k p =tan 2 (45+  /2), and  =3 º for liquefied soil Lateral spreading pressure on piles Rotational stiffness K r was measured before shaking Comparison of Various Methods

21 3D Finite Element Study

22 OpenSees Software Package Beam Element for Pile Solid-Fluid Fully Coupled Element for Soil

23 Conical yield surface in principle stress space and deviatoric plane Shear stress, effective confinement, and shear strain relationship Soil Constitutive Model

24 Ground Response - Acceleration

25 Ground Response - Displacement

26 Ground Response – Pore Pressure

27 Pile Response – Displacement

28 Pile Response – Moment M κ Numerical Actual

29 Deformed Mesh at 10 seconds

30 Pore pressure at 10 s

31 Pile Reinforcement Effect

32 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.

33 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.

34 Thank you !


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