层状地基静压开口管桩的挤土效应研究

Study on soil squeezing effect of open-ended jacked pipe pile in layered ground

采用室内模型试验及PFC 2D离散元软件模拟了静压开口管桩沉桩过程,对桩周土体的挤土效应进行宏观、细观分析。通过模型试验,对在均质硬层和上硬下软两种地基中静压开口管桩过程中产生的位移场进行对比分析,获得了桩周不同位置土体的三种位移变化区域,分别为以斜向上位移为主的浅表层区域,以径向位移为主的桩侧区域和以斜向下位移为主的桩端侧向土体区域,揭示了桩周不同位置处土体位移在水平和深度方向的变化规律,特别是在软硬土层分界面处,土体在水平方向位移值达到最大,且沿深度方向的运动趋势更加明显。以模型试验为基础,建立了静压开口管桩沉桩颗粒流模型,进行数值模拟,并将数值模拟结果与试验结果进行对比分析,分析表明两者较为吻合。通过特征点位移路径分析了土体细观变化模式:均质硬层土颗粒运动轨迹呈现出“J”状,上硬下软双层地基土颗粒运动轨迹近似为“><”形。

Indoor model test and PFC 2D discrete element software were used to simulate the sinking process of open-ended jacked pipe pile,and the soil squeezing effect around the pile was analyzed from the aspects of macro and micro.Comparative analysis of displacement fields generated by open-ended jacked pipe pile into homogeneous hard layer and upper hard and below soft foundations was analyzed by model test,three displacement change patterns of soil at different positions around the pile was obtained,respectively,the shallow layer region dominated by oblique upward displacement,the pile side area dominated by radial displacement and the pile tip lateral soil area dominated by oblique downward displacement,and the variation laws of soil displacement in the horizontal and depth directions at different locations around the pile was revealed,especially at the interface between soft and hard soil layers,the displacement of the soil reaches the maximum in the horizontal direction,and the movement trend along the depth direction is more obvious.Based on model test,a particle flow model of open-ended jacked pipe pile was established,and the numerical simulation was carried out.The numerical results and test results were compared and analyzed,the analysis shows that the two are relatively consistent,and the microscopic variation pattern of the soil was analyzed by displacement path of feature points:the particle motion trajectory of the homogeneous hard layer soil presents a"J"shape,the particle motion trajectory of the upper hard and below soft foundations soli is approximately in the shape of"><".