Seismic Response Analysis And Damping Measures Of High-filled Open Cut Tunnel In High-intensity Seismic Region

Due to the special geological background and geographical environment,earthquake disasters occur frequently in the loess area.The geological conditions around the high-filled open cut tunnel are complex and it's foundation bearing capacity is weak.At the same time,it will cause damage to the door and hole of tunnels if encountered a strong earthquake.The phenomenon of earthquake damage such as axial cracking of cave will also occur.There are few studies on seismic analysis and damping measures for the high-filled open cut tunnel in high-intensity seismic regions.The study of dynamic responses of different underground structures still need to improve.Based on the project of Changshoushan open cut tunnel,this paper studies the dynamic response laws of structure and finds the key parts of seismic fortification.By analyzing the variation of dynamic response of the damping layer to the open cut tunnel,obtaining reasonable thickness and material of damping layer.It provides an important basis for seismic and shock absorption to the open cut tunnel.The specific content includes the following aspects:(1)Learning the main achievements of seismic analysis and shock absorption research at home and abroad by reading a large number of documents,at the same time,introducing the commonly theory of underground structure dynamic analysis.Then,determining the constitutive model of material,seismic wave,damping condition and boundary condition for modeling.The values of each parameter are determined by referring to the data and calculation.(2)Using the finite element software to establish the 3D model of the open cut tunnel,and the seismic response was obtained by inputting seismic waves in three directions:horizontal,vertical and vertical.Through the simulation,following conclusions are drawn:Firstly,The largest displacement and acceleration response of structure is appear at the hole section,the maximum displacement is 8.17cm and acceleration is 2.13m/s~2.The displacement and acceleration show a decreasing trend with the increase of distance from the hole,at the same time,the decrease trend is getting slower.Secondly,The horizontal seismic wave has the most obvious influence on the internal force and stress of structure.The maximum principal tensile stress,shear force and bending moment peak appear at the arch foot and the values are 1003.8kPa,99.21kN,45.62kN·m,the maximum pulling force is 51.62kN.So the structural changes of the arch and waist are the most important parts for seismic fortification.Thirdly,This paper analyzes the influencing factors of seismic performance of open cut tunnel by changing the stiffness of the protection structure and backfill material.According to the comparative analysis of numerical simulation,it can be known that increasing the stiffness of protective structure can weaken the seismic response in a certain extent.Compared with the original working condition,the maximum tensile stress of monitoring point is reduced by1.8%-11.4%,and the axial tensile force is reduced by 1.3%-19.3%,the bending moment is reduced by 0.22%-36.58%,and the shearing force is reduced by 0.98%-34.84%;when using foam concrete in backfilling of the open cut tunnel,it also can weaken the seismic response and make the structure more secure.(3)When analyzing the damping measures of the open cut tunnel,this paper mainly study the influence of material properties and thickness by setting the damping layer between the main body and protective structure of the open cut tunnel.The damping effect of rubber material is better than foam concrete.When laying 15cm or 25cm shock absorbing layers,it can be seen that the 25cm shock absorption effect is better.So,it is recommended to choose the 25cm rubber shock absorbing layer in actual engineering.