Pseudo-static Analysis Method Of Pile Group Earthquake Response In Liquefying Mild Inclined Sloping Ground

The investigation of earthquake damage shows a lot of pile foundations have been subjected to severe damages due to liquefaction-induced lateral spreading during past earthquakes.The dynamic response of soil-pile interaction in liquefaction-induced lateral spreading ground is very complicated under the action of seismic loads,of which there is no unified understanding at present.Therefore,properly understanding the behavior of pile foundation during lateral soil flow is of major concern to both academicians and practitioners.Dynamic p-y curve method is an effective way to evaluate dynamic pile-soil interaction,which defines the relation between lateral soil pressure and the relative displacement of soil and pile.This approach requires that an appropriate p-y relationship be adopted,considering soil conditions.Although,some recent studies were carried out to more fully understand the behavior of p-y curve in liquefied soil,their studies were mainly concerned with smaller soil deformation on the level ground.However,in reality,piles undergo large soil deformation in the case of liquefaction-induced lateral spreading.Therefore,in the present paper,2D numerical analysis was performed to study the pile response in a mild slope under lateral spreading considering pile-soil interaction.The 2D model was validated by using centrifuge test.Based on proven modeling methods and centrifuge tests,develop a 2D full-scale model.Next,using the 2D analysis,dynamic p-y curve were computed.The important conditions affecting p-y curves were analyzed.The modified p-y curves of liquefying sand in a mild slope under lateral spreading was created and the pseudo-static analysis based on Beam on nonlinear Winkler Foundation for analysis of dynamic pile-soil interaction in a mild slope under lateral spreading was suggested.The important research content and results are as follows:First of all,a 2D finite element model was established for centrifuge test in a mild slope under lateral spreading.ABAQUS was used as pre-processing software,Open Sees was used as the computing platform,and GID was used as post-processing software.The saturated sand and clay were simulated with a multi-yield-surface plasticity constitutive model,the pile was simulated using beam-column elements.Consider the effect of free water through static load and pore pressure.Zero-length elements were added to simulate the characteristics of soil-pile contact surface on the basis of rigid soil-pile connection.The results of the 2D finite element model analysis was in reasonable agreement with the centrifuge test data.Secondly,based on the verified modeling methods and centri fuge tests,a full-scale model of soil-pile dynamic interaction in a mild slope under lateral spreading was established,and the basic characteristics of the dynamic p-y curve of the liquefied sand in a mild slope were analyzed,which was different from the dynamic p-y curve of the liquefied sand on the level ground.When the soil was about to liquefy,the earth pressure acting on the pile was the largest,at this time it could be regarded as the critical state of the pile foundation.After the soil was completely liquefied,the soil pressure acting on the pile foundat ion was closely related to the flow velocity of the liquefied soil,which showed the fluid characteristics of the liquefied soil.The degree of restraint at the bottom of the pile foundation and the pile cap had a great influence on the peak bending moment distribution of the pile body.The effects of ground inclined angle,pile diameter,loading amplitude and pile position on the dynamic p-y curve were studied,and these factors were found to have significant effects on the dynamic p-y curve.Comparing the calculated p-y curve with the saturated sand p-y curve recommended by the API and p-multiplier factor method showed that the use of the saturated sand p-y curve recommended by the API and p-multiplier factor method on liquefied slightly inclined sites had certain limitations.Based on the basic characteristics of the dynamic p-y curve of the liquefied sand in a mild slope,a p-y curve based on the ground inclined angle and burial depth was established by modifying the p-y curve of saturated sand specified by the API.The modified p-y curve was integrated into the p-y spring,Beam on nonlinear Winkler Foundation model was established,and the maximum displacement of each soil layer was input to the fixed end of the spring,and a pseudo-static analysis method was proposed.The pseudo-static calculation results were compared with the calculation results of the 2D numerical model to verify the correctness of the pseudo-static analysis method.The research results of this paper are of great reference significance to the establishment of a finite element numerical model for seismic response analysis of pile foundations in liquefying mild inclined sloping ground,which is helpful to deepen the understanding of the soil-pile group dynamic p-y curve in liquefying mild inclined sloping ground.At the same time,the proposed pseudo-static analysis method for seismic response of group piles in liquefying mild inclined sloping ground can better serve engineering practice.