| With the planning and implementation of major submarine tunnel engineering projects in China,seismic research on cross-fault submarine tunnels is urgently needed.Submarine tunnels often extend for tens of kilometers,and due to the limitations of size,earthquakes can significantly affect the spatial effects on long and large underground structures,resulting in significant differences in seismic motion along the length of the tunnel.This thesis proposes a new non-uniform seismic input method based on the Qingdao Jiaozhou Bay Second Submarine Tunnel project,using numerical simulation methods to consider the effects of seawater hydrodynamics,fault displacement,and other factors,and analyzes the dynamic response characteristics of the tunnel under non-uniform seismic action.Meanwhile,a novel seismic test model box for cross-fault submarine tunnels under non-uniform excitation is designed,providing a theoretical and experimental basis for the development of stress and deformation variations in ultra-long tunnels under non-uniform earthquakes,as well as the evolution of tunnel damage under seawater hydrodynamic effects and fault displacement.The main research work includes the following aspects:(1)Based on previous earthquake damage investigation literature and research on the seismic response characteristics of tunnel structures,the factors affecting the seismic response of cross-fault tunnel structures and the forms of seismic damage of cross-fault tunnel structures were summarized to obtain the distribution characteristics of tunnel damage and the response laws of lining structures in earthquakes.(2)A numerical model was established using ABAQUS software,and the material parameters,artificial boundary conditions,and seismic load input methods for synthesizing spatially non-uniform seismic motion were explained in detail.Additionally,a program was developed using Matlab to achieve viscous-elastic artificial boundary,the synthesis of multi-point seismic motion,and batch processing input.(3)The seismic response characteristics of tunnel structures under non-uniform seismic motion inputs were explored.The differences in soil seismic response were compared among consistent wave input,non-uniform wave bottom input,and nonuniform wave bottom and surrounding inputs,verifying the feasibility of the nonuniform input method proposed in this thesis.The research shows that the response of the tunnel lining under non-uniform seismic input is greater than that under uniform input,and there is a difference in seismic response along the tunnel length.The nonuniform input method considers the spatial effects of earthquakes,providing a more realistic reflection of the force situation of tunnel structures.(4)The additional mass method was used to simulate the seismic response of tunnel structures under different seawater depths.The tunnel structure is mainly influenced by hydrostatic pressure,and the dynamic effect of seawater is not significant.When the water depth is 30 m,the dynamic effect of seawater is most obvious,and the displacement response is only increased by 12.19% compared to the no seawater condition.When the water depth exceeds 30 m,seawater is mainly expressed as hydrostatic pressure,and an increase in water depth suppresses the structural displacement response.(5)The seismic response rules of cross-fault submarine tunnels under non-uniform input methods are explored,comparing the response differences of tunnel structures under seawater hydrodynamic effects,fault displacement effects,and their coupling effects.The study shows that the hydrodynamic effect of seawater will further exacerbate fault displacement,increase the range of fault influence,and thereby lead to more severe earthquake damage.(6)Based on the previous study of vibration table tests on tunnel and surrounding rock seismic damage evolution mechanism,the implementation method of nonuniform seismic motion boundary conditions on a vibration table is explored.A model test box that can consider the combined effects of different depths of seawater and different forms of fault is developed,providing experimental basis for revealing the development of stress and deformation variations in ultra-long tunnels under nonuniform earthquakes. |
