板式基础托换法沉降规律的试验研究

板式基础托换法是利用拟建地下室的部分顶板和底板交替支撑既有建筑物完成开挖土方和施工地下室的方法。托换过程引起地基的不均匀沉降会在上部结构中产生附加内力，从而影响到结构的安全。为了研究板式基础托换法沉降规律，将托换过程分为顶板托换、托换顶板四周的土方开挖、接长坑内立柱、底板托换、托换顶板下方土体开挖等5个工况，进行1:10模型试验，用百分表测量立杆底部位置各工况沉降的变化值并计算出沉降差。从试验的结果可以看出，顶板托换、顶板四周的土方开挖和立柱接长3工况出现了中间大、四周小的“盆式”沉降；而底板托换和顶板下方土体开挖工况出现了中间小、四周大沉降规律。最大不均匀沉降出现在立柱接长工况，底板托换工况之后沉降差减少。因此，立柱接长工况成为引起上部结构最大附加内力的最不利工况。

Test study of settlement law of slab foundation underpinning method

Slab foundation underpinning method is an effective method to develop underground space in existing buildings, which weight can be supported by partial top slabs and base slabs by turns. The additional internal forces caused by differential settlement in underpinning affect the safety of existing buildings. The slab foundation underpinning process was divided into five conditions: top slabs underpinning, soil excavation around top slabs, lengthening columns, base slabs underpinning, and soil excavation under top slabs. In order to study settlement law ,a 1:10 model test was done, in which settlement values of every conduction can be obtained by the dial indicator installed on standing post. The differential settlements can be calculated using the settlement values. The test results indicate that the settlements of column-heels in middle part were larger than ones in around part during the process of top slabs underpinning, soil excavation around top slabs and lengthening columns conditions; while, the settlements of column-heels in middle part were smaller than ones in around part during the process of base slabs underpinning and soil excavation under top slabs conditions. The biggest differential settlement was produced in the lengthening columns, which was reduced after the base slabs underpinning. Therefore, lengthening columns is the most unfavorable condition for causing the biggest additional internal force.