Abstract:The Finite Element method was used to analyze the dynamic response of pile groups in the ground subjected to the liquefaction-induced lateral flow of soils.The u-p Finite Element formulation was used to depict the coupling effect of water and sand soil particles in the Finite Element analysis.A 3D numerical model was developed to analyze the effect of a 2×2 pile group subjected to liquefaction-induced lateral spreading. In this model,sand was simulated using a pressure-independent multi-yield surface plastic model.Clay material served as a nonlinear hysteretic material with a multi-surface kinematic plasticity model,and the pile group maintained its linear behavior in the process of calculation.The clay layer and saturated sand layer were meshed in a 20-node brick element and separately in a 20-8 node element.The boundary of the numerical model was considered as the shear beam boundary,which simulated the shear effect of the soil layer during the earthquake.Finally,the Rayleigh damping method was used to model the damping of the system.The dynamic response of each pile in pile group was compared,and it showed that the bending moment and displacement time history of piles at different depths developed in the same way,and the time of maximum bending moment and displacement of the pile appears to lag behind the time of peak acceleration of the input seismic wave.The maximum bending moment and displacement of the leading pile were larger than the those of the back piles.By comparing the maximum bending moment and displacement,it can also be concluded that,as depth increases,the maximum bending moment first increases and then decreases.The bending moment of the pile at the 2.5 m depth was greater than those at other depths. In terms of displacement,as depth increased,the maximum pile displacement decreased,and the maximum displacement of the pile head was greater than other observed points on the pile.This demonstrated the different behaviors of the pile bending moment response.In order to consider the effect of pile spacing on the pile group effect,several Finite Element models were developed for different pile spacing.This modeling concluded that the maximum bending moment appeared to occur in the boundary of different soil layers.As pile spacing increased,the maximum bending moment and pile head displacement in the group increased.In the pile group with pile spacing equal to 7D (diameter),the maximum bending moment of the each pile was very close.The difference was about 3% when pile spacing was equal to 5D,and the difference was about 4%,when pile spacing was equal to 3D.The maximum bending moment of the first pile group was 10% larger than the bending moment of the second pile group.In the last part of the study,the cause of the pile group effect was analyzed and a basic understanding of the seismic design requirements for this type of pile group was obtained.
