Research On The Mechanism Of Piping In Foundation Pit

Bottom piping may occur in the foundation pit under the confined water pressure, which will make great damage to the engineering. How to control bottom piping in the foundation pit engineering becomes a common problem. Based on the failure mechanism of bearing resistance water foundation pit, the existing calculation methods of inrushing for confined water foundation pit are summarized as followed, balance of the water press and the soil?s weight, considering the shearing and cementation strength, considering the stiffness of the pit, overall consideration of the stiffness and the strength of the pit and neural network model for gush of foundation pit. The mechanism of piping is seen from different points of view in these methods, but these methods don?t make the mechanism exactly and clear.In this paper hydraulic fracturing will be introduced into the study of piping in foundation pit. Effective stress and pore pressures in impervious aquiclude will change under the confined water pressure, at the same time, the deformation will increase, which will reduce the stress in the clay. By the theory of hydraulic fracturing, fissures would emerge in the clay where effective stress is small. The fissures will develop from down to up till it runs through the impervious aquiclude, then inrushing of soil and water will occurs.A series of model experiments is performed to determine the type of failure in the foundation pit to observe the course of piping and prove the applicability of hydraulic fracturing in foundation engineering. Then numerical simulations for the experiments are made, and the results indicate that hydraulic fracturing can be used to explicate piping in foundation pit. At last, an analysis of foundation with weaknesses is made, whose result also prove the conclusion above.