Based on the practical cases of construction,this paper argues that the technical problems of precipitation difficulty in the soft soil containing impervious interlayer can be solved effectively by adopting comprehensive precipitation of light well-point,deep well and sand drain.

Aiming at foundation pits(of impervious aquiclude)with confined underground water in soft soil area,calculation model for piping based on plastic deformation failure is developed from piping mechanism of soil under foundation pits,and the concept of yield stress ratio & judgement standard of piping for foundation pits are presented.