Research On Seismic Dynamic Response Of Non-uniform Layered Site

Seismic ground response analysis is an important research content in the field of geotechnical earthquake engineering,which is the core content of seismic safety evaluation of engineering sites and directly provides the parameter basis for seismic design of upper building structures.For general engineering problems,the horizontal non-uniform characteristics of the soil are ignored,and only the inhomogeneous distribution of the soil in the vertical direction is considered,and the site is simplified to a mechanical model of a semi-infinite space bedrock overlying a uniform horizontal layered soil layer for calculation and simulation analysis.The soil layer of the actual site is not homogeneous,but layered,with nonlinear,vertical non-uniform and horizontal non-uniform characteristics.In a large range of sites and the site soil distribution is not uniform,one-dimensional seismic response analysis cannot truly and effectively simulate the site seismic response,then it is necessary to simplify the site into two-dimensional vertical and horizontal non-uniform site analysis.Therefore,the study of seismic dynamic response of non-uniform sites has important theoretical significance and engineering application value.The paper took the actual engineering site as the research object and used numerical analysis methods to study the effect of vertical and horizontal non-uniformity of the formed soil layers on the dynamic response of the site to earthquakes.The main research works and results are as follows.(1)The ABAQUS planar shear wave vertical incidence soil finite element verification model was established to verify the correctness and reliability of the two-dimensional equivalent consistent viscoelastic artificial boundary and equivalent nodal force ground shaking input method in the ABAQUS two-dimensional model.(2)Based on the soil nonlinearity,the vertical nonuniform overburden soil layer was used as the research object,and the vertical nonuniform soil model was established by using the time domain nonlinear calculation program DEEPSOIL and the general finite element calculation software ABAQUS to study and explore the influence of the vertical nonuniform characteristics of the site on the seismic dynamic response of the site,and the results showed that the onedimensional method of DEEPSOIL and the one-dimensional method of ABAQUS The surface acceleration response spectra calculated by DEEPSOIL and ABAQUS 1D methods had similar spectral patterns and limited differences in spectral values;the surface acceleration response spectra of ABAQUS 2D method had obvious high frequency amplification characteristics;the maximum differences in peak acceleration under different input ground motions were at different depths,but they were basically at the boundary of different soil types.(3)Based on the soil nonlinearity,a two-dimensional model of three boreholes was established by ABAQUS with the horizontal nonuniform site as the research object,and the onedimensional nonlinear results of DEEPSOIL were compared and analyzed to investigate the influence of the vertical nonuniformity on the seismic dynamic response of the site.The higher the input intensity,the more significant the high-frequency amplification;with the increase of the input ground motion intensity,the long-period component of the surface acceleration response spectrum obtained by the two-dimensional method gradually developed to be superior;due to the influence of the horizontal inhomogeneity of the soil layer,the dispersion of the PGA obtained by the two-dimensional method was generally smaller than that of the one-dimensional,which made the two-dimensional present a more obvious site amplification effect;the difference of the peak acceleration obtained by the two-dimensional method along the soil layer.The difference in the variation of the peak acceleration along the depth direction obtained by the two-dimensional method was significantly larger than that of the one-dimensional;the horizontal inhomogeneity of the soil layer obviously enhanced the nonlinear characteristics of the soil,which made the difference between the calculation results of the one-dimensional and two-dimensional further increased.