Research And Application Of The Fuzzy Elastic-plastic Model Of Geomaterials

The highway and high-speed rail are constructed largely with China’s economic development, the stability of the subgrade will be very important for which. The core issue is how to establish a constitutive model which can reflect cyclic loading. Yield surface is completely determined in classical plasticity model, which cause plastic yield surface is discontinuous, but plastic yield surface of geomaterials is fuzzy, contradictions is generated by these; It is not conducive to calculate for more mathematical expression is required under cyclic loading.The membership function and the fuzzy deadline set are imported into the plastic yield function to solve the loading-unloading problem in which the classic yield criterion is adopted to deduce the fuzzy plastic yield function. Taken the strain rate into consideration, the fuzzy elastic -plastic constitutive model is obtained; The membership value and stress state is corresponded. The occurrence of plastic strain and the size of the plastic strain are determined by the membership value, Plastic discontinuous of geomaterials can be described by this mode; Calculation will be simplified for complex mathematical expressions are replaced by the evolution of the membership function.The evolution of triangle membership function is studied under cyclic loading and unloading、symmetric cyclic loading and unloading、asymmetrical cyclic loading and unloading, the membership function is used to fix the plastic flow criteria, the partial memory parameters to the maximum stress, which make Cumulative plastic strain can be described by the fuzzy model.The fuzzy cam clay model and fuzzy L-D model deduced by plastic yield function is blurred and associated flow rule. Conventional triaxial test and one-way cyclic loading test are used to test rationality of the model. It is proved to be correct because result of the fuzzy cam clay model and fuzzy Lade-Duncan model fit in result of conventional triaxial test and one-way cyclic loading test.The fuzzy cam clay model and fuzzy L-D model is introduced into the ABAQUS by UMAT which is material subroutine model which was developed by Fortran.Plastic deformation of subgrade is studied by the fuzzy cam clay model. The results of vertical displacement and stress and strain are obtained. Relationship between cumulative plastic strain and dynamic stress ratio、average stress、cycles are obtained; The results of deformation and stress and strain and PGA are obtained by the fuzzy L-D model.The fuzzy elastic-plastic model is obtained by the classic elastic-plastic model which make plastic model need not be established again, the more plastic model will be applied under this idea.