Study On The Influence Of Covered Karst Cave On Xintongziling Tunnel Under Earthquake

The karst area in China is widely distributed in many areas.Due to the interaction between groundwater and surface water in the karst area,the lithology around the karst area is poor,and various types of caves are developed,which poses certain safety hazards to the tunnel construction.Under the action of earthquakes,this hidden danger will become more obvious.Therefore,it is particularly important to analyze the dynamic response of hidden karst caves under karst geological conditions.Based on Xintongziling railway tunnel project as the research background,this paper adopted MIDAS GTS NX software finite element numerical simulation,discussed the stability of surrounding rock and the safety of secondary lining structure under 22 working conditions including different positions,different outer distances,different cave forms and different cave fillings of the tunnel.The research content of this paper is as follows:(1)Analyzed and discussed the stress states at each stage of the tunnel,and elaborated the criteria for the stability of surrounding rock and the safety of lining structure used in this paper.(2)Elaborated the key problems of dynamic analysis,such as the simplified model and parameter,the selection of seismic wave,selection of boundary conditions,characteristic value analysis principle,the time history analysis principle,etc,set up the tunnel buried deep 2 D~ 12 D(D means the tunnel span is 6.25 m)for a total of six calculation and analysis of finite element model,determined the subsequent numerical simulation analysis of tunnel buried deep is 8 D.(3)Calculated the surrounding rock and lining's each 8 monitoring of displacement and stress when the karst cave in tunnel is on the left,top,bottom and distance of 0 m(without cave),1 m,3 m,5 m,7 m with the tunnel under the action of earthquake by using finite element software.Analysed the seismic dynamic response rules of surrounding rock and lining,and it is concluded that the surrounding rock and the safety factor of the second lining.(4)Combined with the actual karst cave situation of the Xintongziling tunnel to establish the calculation model and then calculated the surrounding rock and lining's each 8 monitoring of displacement and stress when the cave shape is spherical,ellipsoid,cylinder,cave is non-filling,half-filling,full-filling under the action of earthquake.Analysed the seismic dynamic response rules of surrounding rock and lining,and it is concluded that the surrounding rock and the safety factor of the second lining.