桩顶荷载对软土地基-群桩基础动力相互作用的影响与机理分析

Influences and mechanisms of loads at pile top on dynamic interaction between soft soil-foundation with pile groups

设计并实施了软黏土地基-群桩基础体系的动态离心模型试验,通过设置两组不同桩顶荷载的模型预制桩,在50g重力加速度环境下,获取了天然地震动作用下软黏土层的加速度、承台横向位移及桩身弯矩,并据此推导计算了桩身竖向变形、桩土相对位移与桩周土抗力,分析研究了桩顶荷载对软黏土-群桩基础体系地震动响应的影响及作用机理。结果表明:①在地震作用下桩身弯矩的反应结果比较复杂,当桩身弯矩沿深度方向出现唯一零点时,桩身弯矩随埋深的增加呈现出先减小后增大又减小的趋势,且桩顶荷载增加时出现这一情况的概率提高了7.58%;②桩顶荷载对桩身弯矩有一定的影响,桩顶荷载增加时,桩身弯矩的最大值随之减小7%,桩周土抗力随之增大25.32%;③软黏土发生震陷时,土体相对位移在桩-土相互作用中起主导作用,桩周土抗力与桩身弯矩的最大值均出现在土体相对位移最大值附近。

A dynamic centrifugal model test is designed and implemented for the soft clay—pile group foundation system.Two sets of prefabricated piles with different vertical loads are arranged,and the acceleration of the soft clay layer,lateral displacement of the bearing platform,and bending moment of the pile under natural seismic action are obtained under 50g gravity acceleration environment.Thus,the vertical deformation of the piles,relative displacement of the piles and soil,and soil resistance around the piles are derived and calculated.The influences and mechanisms of vertical loads on the seismic response of soft clay—pile group foundation system are analyzed and studied.The results indicate that:(1)The results of the response of bending moment of the piles under seismic action are complicated.When the unique zero point of bending moment of the piles occurs along the depth direction,the bending moment of the piles exhibits a decreasing tendency,then increases and decreases with the increase of the buried depth,and the probability of this case increases by 7.58%with the increase of the loads at pile top.(2)The loads at pile top have a certain effect on the bending moment of the piles,and the maximum of the bending moment of the piles decreases by 7%and the resisting force of the soils around the piles increases by 25.32%with the increase of the loads at pile top.(3)When the soft clay soil undergoes seismic subsidence,the relative displacement of the soils plays a dominant role in the pile—soil interaction,and the maximum values of the resistance and bending moment of the soils around the piles both appear near the maximum value of the relative displacement of the soils.