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 Hello everyone, today I am glad that I can present you my dissertation “Liquefaction-induced lateral spreading and its effects on pile foundations”. First of all I would like to thank the professors on my committee. Professor elgamal, professor ashford, professor luco, professor minster and professor murakami UCSD

One-g Shake Table Experiments Laminar Soil Box Rigid Soil Box After clarifying the relevance of vertical motion to lateral spreading, I conducted a series of shake table experiments to study pile behavior during lateral spreading. Among the experiments are 3 using a rigid wall soil box, another 3 using a mid-size laminar soil box, and 4 using a large laminar soil box. Laminar Soil Box

UCSD Shake Table Experiment with a Rigid Soil Box (1) This slide shows the setup of the first experiment using the rigid wall soil box. The soil profile consists of a 1.8 m saturated fine sand. Length and width of the model are 5 and 1.2 m respectively. The slope of the ground surface is about 3 degrees. Relative density of the model is about 40%. A 15 cm diameter concrete pile fixed at the base was tested. Shaking is applied in the direction perpendicular to the longitudinal direction

UCSD Shake Table Experiment with a Rigid Soil Box (2) This is the setup of the second test using the rigid wall soil box. The soil profile is the same as in the first test. Two piles consisting of 10 cm diameter aluminum tubes were tested . They were installed one behind the other to examine pile shadowing effects.

UCSD Shake Table Experiment with a Rigid Soil Box (3) In the 3rd experiment, two piles consisting of 10 cm diameter aluminum tubes were installed side by side examine pile group effects. The soil profile is also the same as in the first experiment.

Model Shaking Time (s) The input motion used in the experiments has an amplitude 0.4 g and a frequency 3 Hz. This is a movie showing the first experiment. Here is the pile at downslope of the slope. Water table just covers soil downslope of the pile. Red grid was painted on the ground surface to monitor displacement. Shaking is applied in the direction perpendicular to the longitudinal direction. During shaking, you will see soil moving toward downslope.

Three Shake Table Experiments with a Laminar Box This slide shows the setup of the experiments using the mid size laminar box. The soil profile consists of 1.9 m saturated fine sand. Length and width of the model were 4 and 1.8 m respectively. The box was tilted 2 degrees on the shake table to simulate an infinite slope. Relative density of the model is about 40%. A 25 cm diameter pile was installed at the center of the model. In the first experiment the pile consisted of a plastic tube and in the second and third experiments consisted of an aluminum tube.

Experiment Model Preparation This picture shows the installation of the pile.

Model Shaking – Top View Time (s) The input motion used in the experiments is a .25g 1 Hz sinusoidal acceleration. Here I would like to show you a movie of the 2nd experiment using the mid-size laminar box. On your right is upslope of the model. The pile was located in the center. During shaking, you will see the model will move toward downslope on your left side.

Model Shaking – Side View This is a side view movie of the model shaking. Upslope is on your left in this view.

UCSD-Japan Joint Research This picture shows the large laminar soil box. It’s 12 m long, 6 m high and 3.5 m wide.

6m high, 0.3m diameter Pile, Shake Table Tests Unliquefiable crust over liquefiable layer Whole soil layer is liquefiable Two soil profiles were tested in this large soil box. In one case, the soil profile consisted of 4 m liquefiable fine sand overlain by 1 m nonliquefiable crust. In the other case, the entire soil layer is liquefiable fine sand. Relative density of the model is about 40%. Two piles with diameter of 30 cm were tested. They consisted of steel tubes. The pile at downslope is relatively stiffer than the pile at upslope. Again the soil box was tilted 2 degrees on the shake table to simulate an infinite slope. Input motion was 0.2 g, 2 Hz sinusoidal acceleration.

Model Response During Shake Table Experiments Pile moment Free field excess pore pressure Here is typical model response during one of the large soil box experiments. In this experiment, the entire soil layer consisted of liquefiable sand. Two single piles were tested. On the left is measured moment time histories of the stiff pile at various depths. We can see that pile moment increases with depth. On the left are measured free field excess pore pressure time histories at different depths. They indicate that the ground liquefied at the first few cycles of shaking. No strong dilation in the soil was observed from pore pressure time histories.

Model Response During Shake Table Experiments Free field acceleration Free field displacement This slide shows free field acceleration and displacement time histories. Near ground surface, acceleration was very small after liquefaction. This is due to the fact that liquefied soil has very low stiffness and strength. Maximum displacement occurred at ground surface. After liquefaction, ground displacements at all depths kept increasing cycle by cycle.

Model Response During Shake Table Experiments Excess pore pressure downslope the stiff pile Excess pore pressure upslope the stiff pile This slide shows excess pore pressure around the pile. At downslope of the pile, pore pressure in the soil had large dips, while the pore pressure at upslope had smaller dips. This is because the soil at the downslope side of the pile tried to move away from the pile and water in this area was stretched.

Model Response During Shake Table Experiments This figure compares pile head displacement of the stiff pile and free field ground surface displacement. We can see after liquefaction, pile displacement gradually decreased and the ground displacement kept increasing as shaking continued. This indicates that soil flowed around the pile after liquefaction. All shake table experiments of this study show similar soil and pile response.

Model Response Summary 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. Free field excess pore pressure reached initial effective stress at the first few cycles of shaking, indicating soil liquefied relatively early. Pore pressures at the downslope side of piles showed larger dips due to the fact that soil moved more than the pile. No strong dilation in the soil was observed during the experiments. After liquefaction, soil accelerations near ground surface decreased significantly and ground displacement kept increasing as shaking continued. 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. These responses are summarized here.

Maximum Moment and Pressure Profiles Top view of Test Setup Maximum Moment and Pressure Profiles Analyses of the experiments focus on lateral soil pressure on the pile at the time step when pile had maximum response. Recall that 3 experiments were conducted using the rigid box. Measured maximum moment profile along the concrete pile during the 1st experiment is shown by the red circles in this figure. The profile along the front pile during the 2nd experiment is shown by the red circles in this figure. The profile along the trailing in this experiment is shown by the plus sign here. Measured maximum moment profiles along the piles in the third experiment are shown here. Based on the measured moment profile, I back-calculated a uniform soil pressure for each pile that can approximately reproduce the measure moment.

Free field ground surface displacement Back-Calculated Maximum Uniform Soil Pressure Test Maximum pile response Free field ground surface displacement Soil pressure (kPa) Pile Mmax (kN·m) Pile head deflection (cm) At the same time as Mmax At end of shaking Rigid1 Left pile 0.63 N/A 5.5 Right pile 0.64 Rigid2 Front pile 1.4 11.0 Trailing pile 0.53 4.5 Rigid3 Single pile 1.86 11.5 UCSD1 2.65 4.2 8.5 12.5 7 UCSD2 3.00 1.6 2.8 7.8 6 UCSD3 2.83 1.2 1.9 2.5 Japan1 Stiff pile 86 10 27 22 Japan2 118 12 8 15 25 Japan3 166 14 19 52 40 Flexible pile 183 43 Japan4 132 11 13 105 95 21 Using the same procedure, I also back calculated a uniform soil pressure for all other piles. They are listed in the last column in this table. We can see that the uniform soil pressure varies from case to case. For long piles in the large soil box experiments, the pressure is much higher than 10 kpa recommended by Dobry. Because the uniform pressure varies from case to case, it would be very difficult for engineers to determine a uniform pressure to design piles against lateral spreading. So we have to find a better way for engineers. Recall that soil failed against the pile and flowed around the pile after liquefaction. This suggests a passive failure mechanism of the upslope soil against the pile. This passive failure mechanisms has been observed during the experiments and past earthquakes.

Comparison of Various Methods Lateral spreading pressure on piles Pile Dobry et al. (2003) Japan Road Association (2002) p=10.3 kPa p=0.3gtz This study shows passive failure of uphill soil Ground Surface z Liquefied Soil Lateral Spreading This slide illustrates the difference between the proposed method and current design methods for the case of a liquefiable ground without a nonliquefiable crust. Basically, soil pressure from the proposed method is higher than current design methods. p=kpgtz, kp=tan2(45+f/2), and f=3º for liquefied soil Rotational stiffness Kr was measured before shaking

3D Finite Element Study

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

Soil Constitutive Model Pressure dependent multi-yield surface constitutive model was used to simulate the saturated soil. Conical yield surface in principle stress space and deviatoric plane Shear stress, effective confinement, and shear strain relationship

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. After concluding this dissertation, I would like to make the following recommendations for future research

Thank you !