Study On Site Classification Method Considering The Influence Of Soil Structure

The site conditions have an important influence on the propagation of seismic waves and the design ground motion parameters.The site type is the basis for determining the design response spectrum characteristic period and adjusting the design response spectrum platform values.Therefore,the site classification still needs to make a further research.Previous studies showed that the site seismic response analysis depends not only on the thickness of the soil layer and the equivalent shear wave velocity but also on the soil structure.The current dual-index site classification method used in China cannot reflect the influence of soil structure on the dynamic response.In order to overcome such limitations,a new site classification method based on periodic equivalent shear wave velocity is proposed in this study.The accuracy of this method is validated and then is applicated to the real cases.The main work of this thesis can be summarized as follows.1.The research status on site classification is summarized in current practice.The development of site classification methods in China is introduced briefly,the main problems are pointed out,and the future research directions in this research field are given.Moreover,the advantages and disadvantages of different classification methods are compared and analyzed.2.The limitations of current site classification method used in China cannot reflect the impacts of soil structure on the ground motion are illustrated by several cases.The artificial seismic waves are selected as the input ground motions,and the four types of sites whose shear wave velocity increases with depth are selected as the calculation cases according to the seismic codes.The influence of soil structure on ground motion parameters is discussed by changing the soil shear wave velocity profiles.The results show that the design ground motion parameters in the same site type but with various soil structures are quite different.The transfer function method is recommended to calculate the site fundamental period.3.The equations of periodic equivalent shear wave velocity are proposed.First,the site fundamental period is deduced based on the layer-by-layer single-degree-of-freedom method.Then,the periodic equivalent shear wave velocity can be calculated.The sensitivity analysis of the travel time equivalent shear wave velocity and the periodic shear wave velocity to the soil structure are performed.The rationality of using two equivalent shear wave velocities as the site classification index is analyzed.4.A site classification method considering the influence of soil structure is proposed.A site classification method using the periodic equivalent shear wave velocity instead of the travel time equivalent shear wave velocity is proposed.The limit value of the periodic equivalent shear wave velocity in the site classification is given.A new siteclassification method that takes into account the influence of soil structure has been developed.