Abstract:

Pile foundation underpinning method can be used to construct the underground space of the existing buildings .The construction processes are constituted three steps: before the pile foundation underpinning, after the pile foundation underpinning and soil excavation. The construction processes produce secondary settlement deformations, which will result in the additional internal forces affecting superstructure safety. Numerical models of three-dimensional finite element analysis based on Ansys code are established to study the settlement of socles on pile foundation underpinning construction for a three-floor frame structure, on which a flat basement is built. The settlement curve and the settlement difference are obtained by defining paths method. Some conclusions are drawn as follows:The total tendency of socles is basin-shaped settlement which is bigger in the middle position socles than the peripheral position socles before the pile foundation underpinning. Pile foundation underpinning augments the differential settlements. After soil excavation, middle position socles rebound obviously owing to unloading action, which lessens the differential settlements between middle and peripheral position socles.The most differential settlement is produced after pile foundation underpinning but before soil excavation. The additional moment of the superstructure can be gained from the finite element model based on Ansys.

Key words: pile foundation underpinning, finite element method, settlement difference, additional internal forces, numerical analysis