Seismic Response Analysis Of Underground Tunnel In Multi-layered TI Saturated Half-space

In recent years,many scholars have studied the scattering of seismic waves by tunnels in different sites,but these researches are mostly limited to isotropic media.Due to the long-term weathering and sedimentation,the natural rock-soil mass shows obvious transversely isotropic(TI)properties.In addition,many tunnels under operation or under construction,such as subways,are located in the saturated areas of the coastal areas,therefore the introduction of TI saturated medium model to study the scattering of seismic waves by lining tunnel has especially important engineering significance in structural seismic resistance.In this paper,two-dimensional multidomain indirect boundary element method is applied to study the scattering of seismic wave by underground lining tunnels in a multi-layered TI saturated half-space.The main work is as follows:1.Based on the Biot's theory,the model of TI saturated half-space is established and the expressions of the displacements of the solid skeleton as well as of fluid,stress and pore fluid pressure are deduced in this paper.Then the accurate dynamic stiffness matrices of a TI saturated soil layer and half-space are derived,and further free wave fields under the incident q P1 and q SV waves are solved.The correctness of the method is verified by comparison with the published results,and the effects of anisotropy parameters and incident angles and other factors on the dynamic characteristics of the site are studied.2.Based on the exact dynamic stiffness matrices combined with the Fourier transform,the Green's functions of a multi-layered TI saturated half-space under uniformly distributed inclined loads and pore fluid pressure in wavenumber domain are derived.The correctness of the method is verified by comparison with the published results,and solutions of displacement(including fluid phase with respect to solid skeleton),stress and pore pressure in the frequency domain in the Cartesian coordinate system under uniformly distributed inclined loads are given.3.For solving the seismic response of lining tunnel in TI saturated half-space under elastic waves,the TI saturated half-space and full-space Green's functions are adopted respectively to simulate the scattering wave field of open domain in multi-layered TI saturated half-space and of lining closed domain;the direct stiffness method is used to solve free wave field,and the total wave field response can be obtained by solving the established boundary conditions.The accuracy of this method is verified by comparing with the existing results,then numerical examples of wave scattering in the lining tunnels in a uniform TI saturated half-space and a single layered TI saturated half-space are given.The results of surface displacements and dynamic stress concentration factor of the lining wall are analyzed,and the influence of anisotropy parameters,surface drainage conditions,wave incident angles and frequency on the seismic response of tunnel is studied.The results show that the anisotropy of media has an important influence on the seismic response of the lining tunnels,and response also depends on the angles and frequency of incident waves,permeable conditions of boundary and other factors.In addition,the scattering effect of the seismic waves on the underground lining tunnels in the saturated area of a single soil layer on a bedrock is quite different from that of a uniform TI half-space.