饱和软土场地中地下结构非线性地震响应分析的一个FEM-IBEM耦合方法

FEM-IBEM coupling method for nonlinear seismic response analysis of underground structures in water-saturated soft soils

基于Biot孔隙介质理论,提出了饱和软土场地中地下结构非线性地震响应分析的一个有限元–间接边界元（FEM-IBEM）耦合方法。方法考虑了饱和土骨架与孔隙水的动力耦合作用及饱和土–结构动力相互作用,并通过等效线性化方法考虑土体的非线性。该耦合方法的特点之一是有限元子域和间接边界元子域相互独立,非常适合并行计算,提高计算效率;特点之二是能够同时考虑有限元子域（近场）和间接边界元子域（远场）的土体非线性。通过与文献结果对比,验证了FEM–IBEM耦合方法的正确性和计算精度。以天津滨海地区一典型深厚饱和软土场地中两层双跨地铁车站为例,计算了地铁车站结构的地震内力和变形,并比较了饱和土体线性和非线性情况下地铁车站地震响应的差别,和饱和土体模型和单相土体模型情况下地铁车站地震响应的差别。研究表明：土体非线性对地铁车站结构的地震内力和变形具有显著影响;饱和土骨架和孔隙水的动力耦合作用对地铁车站结构地震内力和变形也有明显影响。

A finite element method-indirect boundary element method（FEM-IBEM） coupling method is proposed for nonlinear seismic response analysis of underground structures in water-saturated soft soils based on the Biot＇s theory of a poroelastic medium. The FEM-IBEM coupling method can consider the dynamic coupling between solid frame and pore water, dynamic soil-structure interaction as well as soil nonlinearity through equivalently linear analysis. The particular advantage of the proposed coupling method is that the calculations of the FE subdomain and the IBE subdomain are independent as well as parallel. Thus, the soil nonlinearity of both the FE subdomain（near field） and the IBE subdomain（far field） can be considered by avoiding the interactive computation between them. The FEM-IBEM coupling method is validated by comparing with the results in the existing literatures. The seismic internal forces and deformations of a two-story subway station in water-saturated soft soils in Tianjin coastal district are studied. The differences in the seismic responses of the subway station between soil linearity and nonlinearity are compared, and those in the seismic responses of the subway station between water-saturated soils and dry soils（single-phase media） are also compared. It is shown that the soil nonlinearity and the dynamic coupling between solid frame and pore water significantly influence the seismic responses of the subway station including structural internal forces and deformations.