| The excavation engineering involving technologies of wide fields is so difficult to deal with that engineering accidents are frequently happened and brought about a great loss. Besides the great economic loss to the engineering project itself, it jeopardizes the safety of building, underground pipeline, road around, etc. Due to low soil strength, high underground water level and strong soil plasticity flow , unstability accidents happened frequently in soft soil area. Because the strain-stress relation of soil is unable to taken into consideration, the limit equilibrium slice method cannot analyze the process of slope failure. The finite element method (FEM) which has considered the constitutive relation of soil can obtain the actual stress distribution and display the expand process of failure zone. It is a new approach in slope stability analysis nowadays. Based on a excavation accident in soft soil area, and according to the unstability criterion which was suggested by author, the collapse of foundation pit without timbering was analyzed by strength–reduction FEM, and some common characteristics of slope deformation have been obtained. It is shown that the rigid rotation assumption is inadequately fit for soft soil slope, and the shape of slip surface is also not general circular arc surface. Stability coefficient gained by various slice methods cannot meet the demand of actual slope stability. The strength reduction FEM, taking the run-through of plastic zone as unstability criterion, can obtain actual stress distribution and simulate the process of slope failure. It is a method deserving to be advocated Conventional slope stability analysis has not considered the inhibition effect to soil deforming of foundation pile. Actually, foundation pile can be used as anti-slide pile in its deformation allowance. This helpful effect has been discussed preliminarily based on pile-soil interaction , and some significant conclusions have been drawn. |
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