Analysis On Stability Of Karst Tunnel Surrounding Rock At Construction Stage

According to a karst cave in highway tunnel engineering of Yong-Ji Expressway in Naqiu,the finite element software MIADAS/GTS was employed to simulate the excavation process of the bottom karst tunnel.Firstly,the stability evaluation of karst cave,the tunnel construction method,the karst hazard to tunnel engineering and mechanical mechanism of disasters in karst tunnels are studied,secondly the numerical simulation method is used to analyze the influence of different construction method on the stability of surrounding rockmasses during tunnel construction of the bottom karst tunnel.At the same time,Based on the model,the influence of shotcrete thickness,secondary lining thickness and the location of karst cave on the stability of surrounding rockmasses during tunnel construction is further studied.Finally,combined with the field test data,the corresponding conclusions are drawn.The main research contents are as follows:(1)By consulting a large number of literature,the research on the stability evaluation of karst caves and the influence of karst tunnel excavation on the stability of surrounding rockmasses are summarized.The theoretical formula of mechanical mechanism of disasters in karst tunnel is analyzed mainly includes disaster damage of prevention layer and texture faces.(2)Based on the engineering practice and numerical simulation method,the karst tunnels were excavated by using the pre-retaining core soil method,the CRD method and the doubl-wall excavation method,and the displacement and stress changes of the surrounding rock in the construction stage were analyzed.The mechanical rules of the three construction methods are compared and compared with the actual engineering monitoring and measurement data.(3)Based on the method of pr-retaining core soil excavation,the stability characteristics of surrounding rock of tunnel during excavation are analyzed by changing the shotcrete thickness,secondary lining thickness and the location of karst cave.(4)Based on the karst problem encountered in the actual construction of the Nangqiu tunnel,the advanced geological forecast technology of karst tunnel is put forward,and the corresponding treatment scheme is put forward according to the size of the cave and its location.