板式基础托换法开发地下空间施工过程的数值分析

板式基础托换法是应用在既有建筑物地下空间开发中的一种方法。它先施工拟建地下室的部分顶板，依靠板下土体支撑既有建筑物的荷载，同时开挖其余部分的土方。土方开挖后，再施工该区域的柱或墙等竖向构件以及底板；然后，依靠这部分底板支撑上部荷载，完成剩余的土方开挖和顶板、底板的施工。利用ANSYS建立三维有限元模型，分5个工况对托换施工过程进行分析，得到各部位柱脚的沉降规律：在土方开挖之前，中间部位柱脚的沉降大于周边部位的柱脚；土方开挖后，由于“卸载”作用中间部位柱脚出现明显的回弹，使得中间部位柱脚的沉降小于周边部位的柱脚。不均匀沉降值的大小和地基土的弹性模量以及上部结构是否加载有关。不均匀沉降产生的上部结构的附加弯矩可以通过建立二维有限元模型求出。

Numerical analysis of slab underpinning construction in development of underground space

The slab underpinning technology is an effective method for developing underground space of existing buildings. Firstly, after partial top slabs have been constructed, the soil under these slabs support the weight of structure while the soil at the rest places can be dug; then the columns or walls in the basement can be lengthened and the base slabs can be constructed. Secondly, these finished slabs can be taken as underpinning components to support the weight of structure; and the rest jobs such as digging soil under the slabs, constructing the top slabs and the base slabs all can be done. The settlement tendency of column-heels can be gotten by setting up the 3D finite element model using ANSYS program,which can analyze the five phases of underpinning construction. Before the phase of digging soil, the settlement values of column-heels in middle part are larger than those in around part; while, after the phase of digging soil, the settlement values of column-heels in middle part are smaller than those in around part because of the decreasing weight of dug soil. The settlement values have relations with the elastic modulus of soil and increasing load of the building. The additional moments caused by differential settlement can be gained by setting up the 2D finite element model.