Study On Slope Stability Of Foundation Pit Under The Influence Of Groundwater Seepage

The problems of ground water are unavoidable during the excavation of foundation pit engineering in soft fields containing plenty ground water. The changes of ground water level bring the changes of seepage field and stress field. And more, the various kinds of water-seal piles and supported structures are taken in the foundation pit engineering. Those make the mutual actions between soils and ground water more complex. These uncertainty factors have blocked the veracity of the prediction to the foundation pit stability. So, it has not only the theoretic value but the engineering practice value to research the mechanism of ground water and soils mutual actions and the influence of seepage to the foundation pit engineering, then bring forward a new method to predict the safety stability of foundation pit under the ground water seepage actions.Firstly, on the base of stability analysis methods of soil slope, a new method is proposed to estimate the excavation slope stability, combing the strength reduction elastic-plastic FEM and the ABAQUS software. In this new method, software ABAQUS is used to simulate the stress field and analyze the slope stability by adjusting the magnitude of the shear strength reduction factor continuously. With the dynamic manifestation technology of development of soil generalized plastic strain in ABAQUS software, it is regarded as the critical state of slope stability when plastic strain zone has run-through to the top and the generalized plastic strain with the displacement appear infinite development. From the results of some examples, it is found that this new method mentioned above can exactly predict the shape and position of the potential slip surface of excavation slope, and is especially simple and exercisable to describe the properties of seepage field and the influence of seepage force.Then, based on the coupled seepage field and stress field FEM theory, the numerical simulation of seepage field of foundation pit in Jiuhuashan tunnel was done to gain the distribution of the pore pressure, seepage velocity and phreatic surface, analyze the influence of dewatering to ground settlement, and discuss the influence of depths and disposal of draining wells to the descent of groundwater and displacements of the foundation pit. This provides much helpful directions to the draining well design of foundation pit engineering.After that, by the analysis of coupled pore water diffusion and stress, a new method is proposed to estimate the excavation slope stability considering the ground water seepage, which is based on the mechanism of ground water seepage action to the slope soil and the theory of strength reduction elastic-plastic FEM by coupling the seepage field and stress field. In this new method, software ABAQUS is used to simulate the seepage field and analyze the slope stability by adjusting the magnitude of the shear strength reduction factor continuously. With the dynamic manifestation technology of development of soil generalized plastic strain in ABAQUS software, it is regarded as the critical state of slope stability when plastic strain zone has run-through to the top and the generalized plastic strain with the displacement appear...