Abstract:

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.

Key words: slab foundation underpinning method, differential settlement, additional internal forces, model test