上海某基坑超深地墙变形与接缝张开分析

Analysis on Deformation and Joint Opening of Ultra-deep Underground Diaphragm Wall for a Foundation Pit in Shanghai

超深地下连续墙变形所导致的接缝渗漏问题是上海软土地区超深基坑施工所遇到的典型难题之一。结合上海北横通道某深基坑工程,运用Plaxis 3D有限元软件通过计算分析基坑开挖过程不同工况下的地下连续墙的变形规律,以及基坑开挖过程中地墙变形与地下墙接缝张开渗漏的关系。结果表明:当基坑开挖深度大于12 m或20 m两个临界点时侧向位移增长速度显著。地下连续墙的最大水平位移发生在基坑边的中点附近,向两侧逐步减小,这主要是基坑角部空间效应引起的;地下墙接缝张开渗漏的危险点并不是发生在基坑中点最大侧向变形处,而是基坑边中部与角部之间、靠角部较近的位置;即使对于较小尺寸的超深基坑,当开挖深度较大时,长边位移仍较短边位移有明显增大。结论对超深基坑开挖地墙变形与地墙渗漏控制具有指导意义。

The joint leakage problem caused by the deformation of ultra-deep underground diaphragm wall is one of the typical problems met in the construction of ultra-deep foundation pit in the soft soil area of Shanghai. Combined with a deep foundation pit project in Shanghai Beiheng Channel, the Plaxis 3D finite element software is used to calculate and analyze the deformation rule of the underground diaphragm wall under the different construction conditions of excavation process of foundation pit, and the relationship between the deformation and the joint opening of underground diaphragm wall during the excavation of foundation pit. The result shows that the growth rate of the lateral displacement is obvious when the excavation depth of foundation pit is larger than two critical points 12 m or 20 m. The maximum displacement of underground diaphragm wall happens near the midpoint of foundation pit side, and decreases to two sides gradually, which is mainly caused by the spatial effect at the corner of foundation pit. The dangerous point of joint opening leakage of underground diaphragm wall is not at the maximum lateral deformation of foundation pit midpoint, but is between the middle part and the corner of foundation pit side, and is close to the position of the corner. Even for the smaller size ultra-deep foundation pit, when the excavation depth is larger, the long-side displacement still increases larger than the short-side displacement. The conclusion has the guiding significance for the control of the deformation and leakage of the underground diaphragm wall during the excavation of ultra-deep foundation pit.