中深部含软弱夹层的深基坑土钉支护失稳破坏数值模拟分析

Numerical analysis of instability soil-nailing wall in deep foundation pits containing soft soil layer at middle and deep parts

以中核北京科技园综合楼深基坑项目在分层开挖与分层土钉支护中出现的边坡顶端土体开裂、坡底土体坍塌形式的失稳破坏现象为研究背景,运用FLAC3D有限差分软件进行模拟分析。数值模拟分析中考虑土层分布、基坑边坡坡度、土钉的排列方式、钢筋网喷射混凝土面层、含水层的孔隙水压力、分层开挖支护等因素,使模拟分析与实际相接近。根据基坑大小建立相应的基坑边坡三维模型,采用莫尔–库仑弹塑性模型计算基坑边坡在不同开挖支护阶段的位移变形,并通过后处理程序显示基坑整体、最大位移截面的位移云图,记录所设置的关键点处水平位移与沉降量。在工程实际分布开挖过程中,测量每次开挖支护所引起的边坡水平位移与沉降量。将数值模拟中所得节点水平位移、沉降量与两者的实测数值对比分析,由此判断基坑潜在滑裂面与可能出现坍塌的大致位置,为工程设计方案中关于变形量较大区域支护方式的整改提供重要参考。

The FLAC3D software is adopted to simulate and analyze the project based on some unstable and damage phenomena such as fracture of top soils of side slope and collapse of bottom soils of side slope during stagged excavating and construction of soil-nailing wall in a deep foundation pit of the building of Beijing Science Park of China National Nuclear Corporation. In order to ensure the reality of the numerical simulation approach, several factors are considered, in duding distribution of soil layers, gradient of side slope, arrangement pattern of soil nails, reinforced steel shotcrete surface, pore water pressure of aquifer, stagged excavation and support. According to the size of the deep foundation pit, the corresponding three-dimensional model is established. The Mohr-Coulomb elastic-plastic model is used to compute the displacement deformation of side slope at different excavation and support stages, and the displacement deformation nephogram of the whole deep foundation pit and the maximum displacement cross-section are acquired through the post-processing procedure. The horizontal displacement and settlement at several key nodes are recorded. The horizontal displacement and settlement of side slope caused by excavation and support in actual project are measured. The numerical results with are compared the measured data to determine the approximate position of potential sliding surface and collapse in the deep foundation pit. Thus it may offer some important reference for improving supporting pattern for the area with large the displacement in the design.