| The Loess Plateau is located in the western of China,it is a region prone to strong earthquakes,and easily induces large-scale dense continuous loess landslides.With the in-depth implementation of the western development strategy and the "Belt and Road" strategy,a large number of transportation infrastructures are being constructed in western of China.As one of the main structures of the traffic lifeline project,when the tunnel is built in the Loess Plateau with crisscross gullies,it is easy to form a loess bias tunnel near the mountain at the entrance and exit of tunnel.The earthquake damage investigation shows that the shallow buried bias zone of the tunnel portal is the prone part of the earthquake damage of the tunnel,also the loess has the mechanical characteristics of dynamic vulnerability.Therefore,it is great significance to study the seismic response characteristics and damage mechanism of the Loess Tunnel in the shallow bias section.In this paper,based on the actual seismic damage phenomenon of the shallow bias section of the tunnel portal,the response characteristics and damage mechanism of the shallow bias large section loess tunnel are studied by using the method of numerical calculation and model test.The main achievements are as follows:(1)On the basis of collecting examples of tunnel earthquake damage,summarize the seismic damage types and deep analysis of each type earthquake damage.It can provide guidance for the study of seismic damage characteristics and mechanism of large section shallow buried bias loess tunnel.(2)Summarizes several boundary conditions commonly used in seismic analysis of underground structures,and analyzes the advantages and disadvantages of various.Based on viscoelastic boundary,derivation the ground motion input method of SV wave oblique,compiles the corresponding calculation program in general FEM software-ANSYS,automatic application of viscoelastic artificial boundary and equivalent node load is realized(3)Based on the ground motion input method of SV wave oblique incidence,divided into the input direction of the seismic wave are toward slope and back slope,obtained that back slope input of the seismic wave is bad for the seismic resistance of shallow buried bias tunnels;Analyzed the influences of bias angle,thickness of soil cover and incident angle of seismic wave on dynamic response characteristics of large section loess tunnel with shallow bias,the stress distribution characteristics of the tunnel lining structure,the vulnerable parts of the tunnel lining and the order of the influence on the dynamic response(the incident angle of the seismic wave > bias angle > thickness of the cover soil),the failure parts and characteristics of the surrounding rock and slope are obtained.(4)Based on the shaking table model test,studied the seismic response characteristics of shallow buried bias large section loess tunnel,obtained the change rule of acceleration amplification coefficient of slope and slope body,the influence area of tunnel structure on slope amplification,horizontal direction is 0.2-0.8H and 0.2-0.6H in vertical direction and the position with the greatest influence at 0.4H.In addition,obtained the variation rule of acceleration amplification coefficient of slope top with loading amplitude,the deformation and stress characteristics of tunnel lining,and the acceleration response characteristics at the characteristic parts of tunnel lining.(5)Through summarizes the failure evolution process and failure characteristics of the slope and lining during the shaking table model test of shallow bias large section loess tunnel,put forward the failure mode and mechanism of slope,surrounding rock and lining structure of shallow buried biased large section loess tunnel under earthquake load,and combined with earthquake damage instance,verified the failure characteristics of tunnel slope and vulnerable parts of tunnel lining obtained from numerical calculation and model test. |
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