Numerical Simulation For Wave Motion In Two Dimensional Elastoplastic Soil Layer

Analysis of the dynamic elastoplastic response of soil layer is one of significant subjects in the fields of soil dynamics and engineering seismology. The nonlinear viscoelasticity constitutive models or the modified classical plasticity models of soil have been used in general. The dynamic characteristic of soil can not be described accurately using these models especially in complex dynamic loading conditions. The lumped-mass finite element model in conjunction with explicit integral methods, based on the bounding surface plasiticity model of soil, is applied to analyse the dynamic elastoplastic responses of two-dimensional soil layer in this paper. Some available conclusions are obtained and summarized as follows: 1) Based on referring to numerous relative references, the analysis methods of the dynamic response of soil layer are reviewed. The author studies systemically the plasticity mechanics and researches the bounding surface plasticity constitutive model of soil in details. In this paper, an adaptive multistep integration procedure in conjunction with local iteration and radial return is employed in numerical implementation of the bounding surface constitutive model and the subroutine program named as WBSI is coded in Fortran Powerstation 4.0. 2) The dynamic differential equations of the saturated-porous media are discretized in spatial and temporal using the lumped-mass finite element model and explicit integral method. Then the program named as WSDP is coded in Fortran Powerstation 4.0 to analyse the dynamic elastoplastic responses of two-dimensional soil layer. 3) The dynamic elastoplastic responses of soil layer are computed using the coded program. Then the influences of the constitutive models of soil, the stress history states of soil, the artifical boundary and viscous damping are considered. The conclusions obtain as follows: a) The amplitude of elastoplastic displacement becomes larger than that of elastic, and the duration of elastoplastic response becomes longer than the elastic's; b) the results for the cases of K =0.6 and K =0.4 ( K is coefficient of side earth pressure ) are computed, respectively. The comparison of the results shows that displacement response is delayed, the amplitude of fourier spectrum is increased and component of high frequency is decreased according to the descending of K ; c) The dynamic elastoplastic responses of soil layer are influenced by the artifical boundary, then further study is necessary; d) It is not obvious that the influence of damping ratio that eliminates the high-frequency oscillation on the dynamic elastoplastic responses of soil layer if the damping raito is confined in a limited rang. It will be influenced the accuracy of result if the value of damping raito is not proper. At last, the research work are generalized and the problems which need further study in the future are discussed.