Loads Of Changes In Value Of Non-homogeneous Soil Stability Analysis And Its Applications

Under cyclic or transient loading, foundation soils will cause permanent or fluctuating plastic deformations. Such plastic deformations are cumulative or alternating in nature with increase during a sequence of cyclic loading. If the resulting accumulated deformations is limited within a given bound or the alternating deformations will be adapted to a given plastic state after a certain cycle numbers or a certain period of loading, the soils will be in shakedown state. Otherwise, incremental collapse or alternating plasticity will occur. For foundations subjected to loads varying in time in a non-proportional manner within prescribed limits, the limit equilibrium analyses based on the classical limit theorems may overestimate ultimate bearing capacity, as collapse under cyclic loads may occur at a level well below the static collapse values. In such cases, shakedown analyses are of practical significance. Shakedown analyses are aimed to evaluate ultimate bearing capacity of foundations under varied loads. Shakedown theorems, which are generalizations of the limit theorems, can provide appropriate bounds of loads for such complex loading programs.In this thesis, the computational procedure is developed for shakedown analyses and limit analyses. In this procedure, the elasto-plastic finite element method is combined with Melan's theorem of shakedown analyses. Elasto-plastic analyses are performed to obtain elasto-plastic stress field and elastic stress field. Accordingly a residual stress field is constructed. This methodology can avoid the operation of mathematical programming in traditional method of shakedown analysis and therefore obstruction due to large-scale mathematical programming is overcome. The proposed method is applied to evaluate limit and shakedown loads of nonhomogeneous foundations. Different types of non-uniform or layered distributions of soil properties are considered. Based on numerical results computed for different load modes, limit loads and shakedown loads of soil foundations are compared. The ultimate loads and shakedown loads for different combinations of horizontal component and vertical component and moment can constitute envelopes in the load space. Such envelope diagrams can be employed to rationally evaluate the dynamic stability of foundations.