Strength Reduction Fem Analysis On Soil Slope Stability

Strength reduction finite element slope stability analysis method has received people's attention day by day since its creation. The article discussed instability criterions,strength criterions,safety factor search,Accuracy of FEM and the nature solution of FEM about the method. The result indicated:Under the plane strain question, the solution which is similar with the Strict rules limit equilibrium method can be obtained while Mohr-Coulomb inside-tangent circle yield criterion and associated flow rule, or Mohr-Coulomb matched D-P yield criterion and associated flow rule are used. The disparity of them is approximately only in 3%.There are three main criteria for evaluating instability:the non-convergence of solution, the abruptness of the displacement or deformation at a certain characteristic location and the connectivity of plastic zone. Each of them is uniformity and consistency by theories, but the non-convergence of solution is the most convenient and reliable.The calculation accuracy of strength reduction FEM is intimately associated with the choosing of mesh mode. Rougher mesh model is used, the safety factor is bigger. The result gap can be 5% in different density mesh model. The true value of the safety factor is approximated by the enough accurate grids. So it is very necessary to use enough fine mesh models to improve the calculation accuracy.In the partial refinement grid model, the calculation accuracy is more accurate and save more time when the mesh length and height is about 1 in 30.Model boundary has little influence to the calculation accuracy. If the model boundary is wider than the potential sliding surface (or glide), we can obtain smaller model, simplified calculation and efficiency.Elasticity modulus E and Poisson's ratio v of soil Slope also has little influence to the calculation accuracy in the condition of small deformation. The inequality sinφ≥1-2v is not necessary to the solution of the safety factor.The safety factor of Strength reduction FEM has upper limit of value. The theory of Strength reduction FEM is more perfect, so it is more safety generally. Because of this, the calculation upper approximate limit and leaded to insecurity. Limit equilibrium method (article strict method) can get bigger safety coefficient than FEM (About 1%～3%), so it is not superior to FEM.