Parameter Sensitivity Analysis In Numerical Simulation Of Soil Dynamic Problems

Due to the complexity of mechanical properties of soil materials and the semi-infinite field properties of the site and the randomness of seismic action,it makes a series of uncertain factors in the analysis of site seismic response by finite element method.In this context,this paper uses PLAXIS 2D software to conduct a detailed study of several key issues in the field seismic response analysis such as the selection of the lateral boundary distance of site,the bottom artificial boundary,and the simulation of soil material damping.The main work as follows:In this paper,three commonly used artificial boundary types such as viscous boundary,free-field boundary and tied degree of freedom boundary are combined with uniform field model and layered uniform field model to study the selection of lateral artificial boundary distance in seismic response analysis of site.The influence of different shear wave speed,different excitation frequency,different damping ratio,different input wave spectrum characteristics and different constitutive models on the selection of artificial boundary distance are analyzed.The study shows that the ratio of unilateral artificial boundary distance to soil depth L/h is the main parameter affecting the selection of artificial boundary distance.Under horizontal excitation,the effect of tied degree of freedom boundary is the best,followed by the free field boundary,the viscous boundary required the maximum boundary distance;in each factor,different excitation frequency,different shear wave velocity and different damping ratio have little effect on the selection of artificial boundary distance.Different constitutive models and different input wave spectral characteristics have significant influence on the selection of the boundary distance.With the increase of L/h,the calculation error of the finite element model does not always decrease.In the local area,the calculation error will increase with the increase of the boundary distance.Based on the concept of artificial boundary at the bottom,the theoretical and finite element models of seismic response analysis of homogeneous site are compared.The essence of the bottom boundary problem and the possible influence on the calculation result when it is regarded as a fixed boundary are studied.By using the assumption of hysteresis damping,the analytic expression of the surface displacement amplification factor in a homogeneous field containing both radiation damping and material damping is derived.Then the effects of material damping and radiation damping on the amplification factor are studied.The idea of making up for neglected radiation damping by increasing the material damping of the site is proposed.A new method of determining the material damping after radiation damping is given in the finite element modeling.Using the PLAXIS 2D software‘s geotechnical experiment simulation function,the four commonly used constitutive models of geomaterials,Linear elastic model,Mohr-Coulomb model,Hardening soil model and Hardening soil model with small-strain stiffness under cyclic loading are comparatively analyzed.On this basis,the influence of different constitutive models on the results of the free-field seismic response analysis and the sensitivity analysis of the dynamic calculation results under different constitutive models are studied.The research conclusions provide a reference for the selection of constitutive model and the reasonable judgment of the numerical analysis results in the field seismic response analysis.