The Effect Of Surface Soil Structure On Soil Seismic Response

In Code for Seismic Design of Buildings, the site can be clarified into four types, i.e., Type Ⅰ, Ⅱ, Ⅲ, and Ⅳ based on thickness of covering layer and equivalent shear wave velocity. Earthquake investigations show that the change in soil layer construction of sites can result in the different damage degree of engineering structures, even though these engineering structures are placed on the same type of sites. Previous studies indicate that the variation of the structure of covering soil layer, particularly the near-surface soil layer structure, remarkably affect the ground motion at the surface.In this study, nearly200soil profiles are collected or built, based on the actual survey data. According to Code for Seismic Design of Buildings, the soil profiles are classified as different site classes and the effect of surface soil structure (thickness, shear-wave velocity) on ground motion is analyzed for site class I, II and III. By observing the variation of defined variables such as amplification factor M and variation rate β, the influence pattern of the variation of top soil structures on surface ground motion is obtained.In recent years, earthquakes occur frequently. The result of seismic damage investigation shows that, big earthquakes could lead to the damages of not only near-field structures, but also far-field structures, which even suffered severe damages. Therefore, relevant studies about the effect of near-field and mid-field ground motion input on the ground motion at the surface is performed in this dissertation. I choose3typical earthquakes from the American strong motion database, and pick8near-field or far-field ground motion records for each earthquake, based on epicentral distance. Then these records are considered as input ground motions for the specified sites, and the influence pattern of the variation of top soil structures on surface ground motion is obtained by observing the variation of amplification factors and response spectra.The contents of this study are listed as follows:(1) The theory of seismic response and one-dimensional equivalent linear method are summarized.(2) Numerical analyses are performed on200profiles collected using one-dimensional equivalent linear method.(3) The influence of soil layer construction (thickness of surface soil, shear wave velocity) on surface ground motion (peak acceleration magnification, characteristic period of acceleration response spectra).(4) The effects of near-field and far-field ground motion on the surface ground motion are studied.