Scattering Of Elastic Waves By Composite Lining Of Shallow Buried Tunnel In Saturated Stratum

With the development of economy and society,the construction of urban cross-river and cross-sea traffic engineering is increasing day by day,and the underwater tunnel engineering plays an important role.In recent years,a large number of tunnel structures have been damaged due to the frequent seismic activities,which subverts the traditional concept that tunnel structures have good natural seismic performance.Therefore,it is of great significance to study the seismic response mechanism of tunnel structure in saturated stratum,improve its antishock performance,and ensure the safety,smoothness and post-earthquake repair of tunnel structure under strong earthquake.Since the tunnel is located in half space,its seismic response is essentially a scattering problem of waves.On the one hand,the scattering waves affect the ground motion on the surface of half space,and on the other hand,the tunnel structure itself is affected.The seismic wave propagation in saturated soil is significantly different from that in single-phase ideal elastic medium.The seismic response rules and calculation methods of tunnel structures in saturated soil have long been the hot and difficult points.In saturated soil,most of the existing studies are limited to the seismic wave scattering of unlined holes or single-layer lining structures,or only considering the deep buried depth,or only considering the single wave type,and most of them do not deeply analyze the aseismic design of lining structures.In view of this,combined with the existing seismic damage cases,the seismic response mechanism of shallow composite lining tunnel in saturated soil is studied systematically by theoretical analysis and shaking table test.The results can provide theoretical support and test data for the aseismic design and seismic safety evaluation of shallow composite lining tunnel in saturated soil.The main work and research results are as follows:(1)Based on Biot dynamic theory and Fourier-Bessel series expansion method,the scattering mechanical models of P wave,SV wave and R wave of shallow composite lining tunnel in saturated soil are established by introducing large circular arc to simulate the surface.The analytical solutions of dynamic stress concentration coefficient,pore pressure concentration coefficient and surface displacement of composite lining in frequency domain are solved.(2)By parametric analysis,the dynamic response of composite lining and surface are studied,considering the influence of the seismic wave,incidence angle and frequency,stiffness ratio of inner lining to outer lining,thickness ratio of inner lining to outer lining,buried depth of tunnel,porosity of saturated soil and surface permeability.The dynamic fluidstructure coupling mechanism of the water-soil-composite lining structure system under earthquake is revealed,and the corresponding aseismic design parameters are proposed.(3)Shaking table model tests of shallow composite lining tunnel in saturated sand are carried out.The feedback mechanism of the stiffness matching relationship between the composite lining with variable stiffness,thickness and saturated soil on the dynamic response of the model system in different ground motion parameters is studied.By comparing the theoretical solution with the model test results,the correctness of the SV wave scattering model and the credibility of the test results of the shallow composite lining tunnel in saturated soil are proved.