Study On Effective Depth Of Soil Seismic Response

A large number of earthquake damage investigation and seismic observation data show that the site cover soil layer,especially the shallow soil cover layer,has a very significant impact on the seismic response.The influence of shallow soil cover layer on seismic response is mainly manifested as the amplification effect of soil layer.The soil amplification effect leads to obvious effects of seismic damage,and the variability is significantly constrained by the soil conditions.Nowadays,soil seismic response analysis is the main means to analyze the amplification effect of shallow soil cover layer.The seismic response analysis of soil layer can not only provide the parameters such as peak ground acceleration and response spectrum required for seismic fortification of sites,but also give the distribution characteristics of soil seismic response along the depth.The distribution characteristics of seismic response along the depth of the soil layer can be studied to get the depth of shallow soil cover layer.The shallow soil cover layer refers to the effective depth of soil layer that significantly affects the results of seismic response calculations.This paper focuses on the effective depth of soil seismic response.The main research work and conclusions are as follows:(1)In this paper,for the conventional case that the soil stiffness of a horizontal site varies exponentially with depth,the fundamental period of this type of site is solved by using the separation of variables method and the nature of Bessel function according to the problem of initial boundary value of seismic response,and the analytical solutions of displacement,acceleration,stress and strain at each point during an earthquake are given.(2)In this paper,the fundamental period of horizontal non-uniform soil layer is given as a function of surface shear wave velocity,site cover thickness and non-uniform coefficient of soil stiffness,and the variation law of the analytic solution of the fundamental period of the site is analyzed.(3)In this paper,typical theoretical calculation profiles of three types of sites,Ⅱ,Ⅲ and Ⅳ,were constructed,three ground shocks with different sampling frequencies were selected as inputs,and the data calculation of displacement,acceleration,stress and strain with depth for nine groups of working conditions was completed using the seismic response analysis method.(4)This paper establishes a seismic response database based on the strong seismic records of KiK-net seismic network in Japan,and selects 19 working conditions which the software calculation results are close to the actual records by three indicators:peak acceleration at the ground surface,characteristic period of the standard response spectrum at the ground surface and platform value,and analyzes the surface response spectrum,peak acceleration,maximum shear stress,maximum shear strain and characteristic period distribution characteristics along the depth,and selects the peak acceleration and maximum shear stress,which have obvious amplification effect with depth,as indicators to answer the question of the effective depth of soil seismic response.(5)In this paper,eight typical ideal generalized calculation profiles of three site types Ⅱ,Ⅲ and Ⅳ are constructed,the improved SOILQUAKE software is used to calculate the seismic response,the effective depth of seismic response of the soil layer is studied,the guidelines for defining the effective depth of seismic response of the soil layer are analyzed,the peak acceleration and maximum shear stress can be used as typical indicators for defining the effective depth,and the conclusion that the effective depth of seismic response of the soil layer is 30m is given.