Seismic Analysis Of Subway Station In A Site Interbedded By Saturated Two-phase And Single-phase Soil

With the development of city construction the usage of underground is becoming more important. As an important component of lifeline engineering, it's power to resist disaster is especially important. The aseismatic study of underground structures is recognized widely after the Kobe earthquake. Many scholars have engaged in this study and made great progresses.When saturation is less than 90%, the pore fluid can't flow in soil hole. When saturation is between 90% and 95%, this Soil is called nearly saturated soil; When saturation is larger than 95%, this Soil is called saturated soil. When elastic waves propagate in soil, they can induce the interaction between solid-skeleton and pore fluid, for saturated and nearly saturated soils, which can be discribed by Biot dynamics theory. This kind of soil is assumed as saturated porous media. Whereas, for soil whose saturation is less than 90%, there is no interaction between solid-skeleton and pore fluid. This kind of soil is assumed as single-phase soild media, which can be discribed by elastodynamics. In this dissertation, the saturated and nearly saturated soils are named as saturated two-phase soil and the soil whose saturation is less than 90% is named as single-phase soil. The main studies in this dissertation are listed as follows:1. An approximate spring-dashpot artificial boundary conditions of saturated porous media are presented. It is shown that the normal and tangential wave stresses of the solid phase on the boundary are proportional to displacement and velocity, and the pore fluid has only normal wave stress which is proportional to it's velocity on the artificial boundary. Therefore, the continuously distributed springs and dashpots can be set on the artificial boundaries in the normal and tangential directions to absorb the energy of outgoing waves. The wavemotion input can be realized by applying equivalent loads on the artificial boundaries.2. Two methods of analyzing free wave field of interbedded layers are presented. One is the Fourior method. In frequency domain, by the consistent conditions of boundaries and stresses boundary condition on the surface, a linear equations is formed. After solving the equations the wave fields in frequency domain are obtained, then by the contrary Fourior transform, the time domain wave fields can be obtained. The second method is the one dimensional explicit finite element method. Based on the charateristics of propagation of plane waves and concentrated mass FEM and three-point formulas, the motion equations of one list of particles forme a linear equations the variable vector is constituted by the displacement vector of each particle. By solving this equations, the whole wave field can be obtained.3. By the explicit FEM of different time steps, the dynamic response of a momolayer subway station is analyzed, and some important conclusions are obtained. With the increasing of shear velocity of soil, the racking coefficient also increases; For two-phase soil, with the increasing of shear velocity of soil, the bending moment of wall decreases, whereas the bending moment increases for single-phase soil.