Mechanism Research And Particle Flow Code Numerical Simulation Of Piping In Foundation Pit Based On Hydraulic Fracture

Protecting from Bottom piping in deep foundation pit engineering has been gradually a very severe subject. It is difficult to solve the problem connected with confined water, and it might cause great damage to the project if the solution is not proper. Hence, how to estimate exactly the stability of anti-bottom-piping of foundation pit under the confined water becomes more and more important. The existing calculation theories of stability of anti-piping for foundation pit are summarized as followed: simple balance of the water pressure and the soil's weight, considering the shearing and cementation strength of soil, considering the stiffness of the pit, overall consideration of the stiffness and the strength of the pit and statistics and anticipation based on neural network model. These methods have studied the mechanism of piping in different views, but all of them have some drawbacks and have not acquired a clear and deeply acknowledge to the mechanism of piping.We can find that the bottom piping of foundation pit and the hydraulic fracturing of clay core in fill dam, which are two different engineering fields'phenomenon, is very similar in their mechanism. They both have the existence of high water pressure; have formed leak path in clay pan (low permeable layer) and broken due to tension. They both happen abruptly and the phenomenon of crack progressing and hydraulic fracture extension is exactly similar. Therefore there must be some common properties in their occurrence mechanism and condition and calculation method. In this paper, we are attempting to use the hydraulic fracture theory in fill dam engineering for reference to explain the mechanism of piping in foundation pit.To observe the failure process of piping and verify the mechanism, we will use PFC (Particle Flow Code), which is suitable for studying problem with flow (large deformation) and fracture, to build numerical model. We will eventually achieve the simulation of the entire process of piping via a series of parameter analysis and test.