Anisotropic Cosserat Continuum Elastoplastic Constitutive Model And Its Numerical Application

The mechanical characteristics of anisotropy and strain softening generally exist in the rock and soil materials in nature.However,there is still no analytical method that can reasonably and effectively couple the two characteristics in the finite element numerical simulation.To solve this problem,this paper has done the following work:1.The theoretical method of strength anisotropy of microstructure tensor combined stress invariant proposed by Pietruszczak and Mroz is developed from anisotropy analysis of internal friction Angle of non-cohesive soil to cohesive force analysis of cohesive soil.The expression consistent with the classical Casagrande theory of cohesive anisotropy is derived.It is proved that the theoretical method of anisotropy developed in this paper is more reasonable theoretically and numerically.2.In the framework of Cosserat continuum,the anisotropy and strain softening characteristics of cohesive force are taken into account in the Drucker-Prager yield criterion.The consistency algorithm of explicit expression of tangent constitutive modulus matrix is derived.Moreover,UEL is realized through programming under the secondary development of finite element software ABAQUS.The correctness of the finite element model developed in this paper is verified by triaxial test and plane strain test on clay.It also provides a reference for the experimental acquisition of the new parameters of the constitutive model.The stability of soil slope,the passive earth pressure of retaining wall and the bearing capacity of foundation are simulated and analyzed by using the finite element model developed in this paper.It is proved that the model developed in this paper can effectively overcome the ill-conditioned dependence of the classical continuum model on the finite element mesh density when simulating the strain localization problem caused by strain softening.3.In view of the obvious elastic anisotropy of rock mass,the constitutive model of 2-d elastic anisotropy under plane strain condition is derived under the framework of Cosserat continuum.In addition,it is combined with the plastic part of the d-p elastoplastic constitutive structure which is coupled with the strength anisotropy and strain softening characteristics,so as to obtain the d-p constitutive model which can take into account the elasticity anisotropy,strength anisotropy and strain softening characteristics at the same time.Furthermore,the uniaxial compression experiment of layered rock samples is simulated by using this model combined with partition modeling.Aiming at the stability problem of bedding rock slope,the finite element simulation and analysis are carried out by the same modeling method,and the reasonable calculation results are obtained.At the same time,it is found that the classical continuum model also has the problem of poor suitability when simulating the strain local problem caused by strength anisotropy.The model developed in this paper based on the continuum theory of Cosserat can effectively overcome this problem and obtain stable and reasonable simulation results.