Applications Of The Elasto-Plastic Finite Element Method Based On The Shear Strength Reduction Technique To Slope Stability Analysis Under Plane Strain Condition

The elasto-plastic finite element methods based on the shear strength reduction (SSR) technique have been increasingly applied to the numerical analysis of slope stability. In this thesis, the key issues related to these methods are discussed. The main investigations are composed of the following parts.1. Many earth structures such as earth or rock fill dam, retaining wall, embankment and strip foundation can be considered as plane-strain condition. However, at present the shear strength parameters (c,(?)) of soils used in the FEM analyses under the plane strain condition are still determined by laboratory triaxial compression tests. Some correlative tests indicate that the result will be conservative while under plane strain state but still adopting shear strength under triaxial compression. Therefore it is necessary to study on the inter-relationships between strength parameters under plane strain state and triaxial compression state. Basing on the previous studies, correlation formulate for relating the strength parameters of soils under various stress states are established by using the extended SMP criteria. Especially, the strength parameters under plane strain state and triaxial compression state are compared, and the approximate relationship between them is defined using curve-fitting techniques.2. Combining the shear strength reduction technique and the correlation formulae between strength parameters under plane strain state and triaxial compression state, the elasto-plastic FEM based on the shear strength reduction technique is developed to stability analysis of slopes. Moreover, the basic rule of the evaluation of critical overall instable state of slope is used based on the development pattern of generalized plastic strain or plastic zone. A type of elasto-perfectly plastic models called as MCDP is adopted, in which Mohr-Coulomb criterion is taken as the yield function, non-associated flow rule is adopted with a plastic potential function similar to Drucker-Prager criterion. The model can not only accord with the practice but also can avoid singularity in determining the incremental plastic strain.3. The stability analyses of both a natural slope and two natural slopes are performed by the proposed, method. The results are compared with the solutions computed by using the strength parameters under triaxial compression tests. It is shown that the conventional method based on the shear strength parameters obtained in triaxial compression condition is used to underestimate the ultimate bearing capacity of earth structures in the plane-strain condition.4. The object-oriented-programming (OOP) of the proposed method is implemented by using Visual C++, which has not only powerful computational function but also flexible pre-and post-processing function. In the post-processing, the computed results can be expressed by the isograms and color nephogram. The development of generalized plastic strain as the reduction of strength parameters can be observed and the potential failure zone of slope can be visualized by using the dynamic display technique.