Analysis On The Influence Of The Back Cave Of Mountain Tunnel On The Safety Performance Of Lining Structure

In recent years,Chinese transportation infrastructure has developed rapidly,and the traffic demand has been increasing.At the same time,Chinese terrain is complex and there are numerous mountains.Therefore,in the process of demanding construction of highways and railways,tunnels have many advantages.It is widely used,such as shortening mileage,improving routes,and improving economic efficiency.Especially in the southwestern mountainous areas and the southeastern hilly areas,the ratio of the high-grade road tunnels is usually up to 15%to 30%,and the ratio of the high-grade railways to the tunnel lines is even as high as 25%to 50%.Due to the large number of mountain tunnels,serious diseases,and inadequate funding for maintenance in China’s transportation infrastructure,how to carry out reasonable and effective operation and management has become a focus of academic and engineering concern.According to relevant regulations,service performance evaluation of mountain tunnels includes two parts:civil engineering structure and electromechanical facilities,while civil engineering structures are mainly lining structures.Therefore,this paper focuses on the lining structure of mountain tunnels and relies on the Longmen tunnel project in Quanzhou,Fujiain Province.An indoor scale model test was conducted and FLAC3D software was used to simulate the effect of different void positions and cavity sizes on the safety performance of the lining structure.The main conclusions are as follows:(1)In the case of the same cavity behind the lining,the bearing capacity of the lining structure will decrease as a whole,but the lining structure shows basically the same deformation characteristics and stress characteristics.(2)When there is an empty hole behind the lining vault,the hollow area corresponding to the surrounding rock will lose its passive resistance of the surrounding rock and will push out from the original internal tension state to the internal pressure state.The positive moment becomes a negative bending moment.,And with the increase of voids,the larger the moment of change.After the emergence of the right arch waist cavity,the surrounding rock of the right arch waist region is squeezed outward due to the passive resistance of the surrounding rock,and the bending moment is obviously increased,and the bending moment changes more with the increase of the cavity.After the right arch foot hollow is generated,the surrounding rock of the right arch foot is forced out of the wall due to the loss of passive resistance of the surrounding rock,and the bending moment is obviously increased,and the larger the bending moment changes with the increase of the hollow hole.(3)After the cavities are hollowed out,the stress of surrouinling rocks will be redistributed,and stress concentration will occur at the locations of the voids and near the voids.The surrounding rock-secondary lining contact pressure will change after the void is created.The surrounding rock-secondary lining contact pressure near the void location will increase significantly,so it is important to prevent it.(4)After the cavities behind the lining are produced,the safety coefficient of the second lining correspond.ing to the position range of the cavities will decrease,and the safety factor at the center of the cavities will decrease more significantly.When there is a hole behind the tunnel surrounding rock dome,the safety coefficient of the second lining adjacent to both sides of the cavity is decreasing;when there is a hole behind the right arch waist,the safety coefficient of the second lining immediately above the hole decreases,while the safety factor on the lower side It increases,and the safety coefficient of the second liner of the right side wall of the tunnel,the arch foot,and the inverted arch increases with the increase of the void,so when there is a hollow in the right arch waist,the side wall,the arch foot,and the invert arch The safety is favorable;when there is a hole behind the right auger of the surrounding rock of the tunnel,the safety factor of the empty lining and the second lining of the right arch position is decreasing,and the safety factor in the rest is not changed much.