既有单桩在邻近基坑开挖下的水平向响应简化分析

Simplified analysis method for evaluating horizontal deformation of single pile due to adjacent foundation pit excavation

为了探究既有单桩在邻近基坑开挖作用下的水平向响应规律,提出基于虚拟镜像技术的基坑开挖引起邻近单桩水平向响应解析解.发挥基坑围护结构变形易于实测的优势,借鉴虚拟镜像技术,考虑土体位移的实际情况,修正土体的等量径向移动模式,推导出土体非等量径向移动模式下基坑开挖引起的坑外土体水平位移场.基于Pasternak双参数地基,引入修正地基反力模量以考虑埋深效应,利用两阶段法,将土体水平自由位移场视为外荷载施加于邻近单桩,建立在邻近基坑开挖扰动下既有单桩的水平向位移控制方程.与三维有限元数值模型、既有理论解及已发表案例的工程实测数据的对比,验证该方法的正确性及适用性.参数分析表明:提高地基反力系数和单桩抗弯刚度有助于减小单桩最大水平位移;当桩与基坑间距较远时,单桩最大水平位移几乎不再受自身抗弯刚度的影响.

A new simplified analytic solution considering the actual state of ground displacement was proposed based on the virtual mirror technology in order to estimate the response of the existing single pile due to adjacent basement excavation.The virtual mirror technology was used,and the measured deformation of the basement maintenance structures provided easily by the in-situ monitoring technique was utilized.The analytic solution of the greenfield ground movement was developed based on the non-equivalence of the radial movement of the ground.Then the greenfield ground movement was imposed on the pile with the two-stage method by introducing the modified foundation reaction modulus to consider the depth effect of ground.The control differential equation of horizontal displacement of the pile based on Pasternak foundation was established.The feasibility and effectiveness of the proposed method was verified by comparison with three-dimensional finite element method analysis and the existed theoretical solution as well as field measured data.The parametric analysis show that increasing the coefficient of subgrade reaction and the bending stiffness of the pile can decrease the maximum horizontal displacement of the pile.When the pile is far from the foundation pit,the maximum horizontal displacement is essentially immune from the bending stiffness of the pile.