The Mathematical And Mechanical Foundation Of Generalized Plastic Mechanic And A Three Yield Surface Model For Soil

The constitutive model of soils is a basic problem for soil mechanics, and is also the basis of the modern soil mechanics . More than thirty years has past and numbers of models have been put forward since Prof. K.H.Roscoe and his fellows of Canbrudge Ybuversutt established the first elastoplastic model of soils which is based on classical plastic theory in 1963. However, due to the complexity of soil , the models that based on the traditional plastic mechanics have still much limitation when used to express the soil mechanical behavior, and it's very disordered that how many yield surface should be select and how to select flow principle. The generalized plastic mechanics put forward by zhengyingren and other scholarships is developed from the deformation mechanism of geo-materials and traditional plastic mechanics. It is applicable of to metal as well as geo-materials, and can reflect the deformation mechanism of geo-materials perfectly.This paper uses the method of tensor to proof the tenable condition of generalized plastic potential , discuss the mathematical essential of the associated and disassociated flow rule and the relation of the yield surface and plastic potential surface, reason the expression of plastic factor strictly .debate the limitation on Drucker's postulate. Subsequently, this paper gives the mathematical basis of constitutive theory involving the rotation of principal stress axes. So it is proved that the mathematical and mechanical foundation of the generalized plastic mechanic .Furthermore, according to generalized plastic mechanics theory ,a three yield surface model is researched basing on the experiment of other people and the shear yield surface in the stress Lode angle direction is researched emphatically .By the new model, the FEM program is also worked out in this paper. The numerical results show the validity of the model and the effect caused by the yield surface and the rotation of principal stress axes on soil deformation. Lastly, the relative results are got by the comparison and analysis.