Study On The Influence Of Hidden Karst Caves On The Stability Of Heavy-haul Railway Tunnels

The construction disasters of karst tunnel not only affect the construction period,but also endanger the personal safety of workers and damage mechanical equipment.In the past,the disasters encountered in the construction of karst tunnels were mainly caused by exposed karst caves.Unexposed hidden karst caves may cause tunnel collapse and other karst disasters during the later operation period,seriously affecting the stability of tunnels.Therefore,it is necessary to study the safe distance between hidden karst caves and tunnels,and to analyze the influence of hidden karst caves on the stability of tunnels.The measures taken during the construction period have special theoretical and practical significance for ensuring the long-term safety of tunnels in karst areas and improving the design level and construction technology of tunnels in Karst areas.The Mengxi-Huazhong Coal Transport Railway(built into the Menghua Railway)is the longest dedicated coal transport line in China and the first heavy haul railway built in the karst areas of southern China.Considering the actual situation of hidden karst caves encountered during the construction of the tunnel in Jiangxi Province of Menghua Railway,considering the influence of train vibration load on the hidden karst caves during the later operation period of the tunnel,the influence of hidden karst caves on the stability of the tunnel is studied by theoretical analysis and numerical simulation.By collecting the data of karst tunnels in southwest China and the investigation of Heavy-haul Railway Tunnels in Inner Mongolia-Jiangxi,and collecting the data of existing karst tunnels,assuming the size and spatial distribution of hidden karst caves,the corresponding analysis models of hidden karst caves and tunnels are established.Based on different types of hidden karst caves,ANSYS and FLAC3 D are used to study the working conditions of hidden karst caves under the tunnel,side wall and foot of the wall,and to carry out numerical simulation analysis of the influence of train vibration load on the stability of the tunnel during tunnel construction and later operation.Based on the analysis of various working conditions during construction,the distribution of plastic zone between tunnel and hidden karst caves at different locations,the mechanical properties and displacement monitoring of tunnel structure are analyzed,the stability of surrounding rock is evaluated,and the critical safety distance between tunnel and hidden karst cave is obtained.On this basis,the model under the critical safety distance between tunnel and karst cave is selected,and the vibration load of Heavy-haul Train in later operation is considered.The dynamic response of tunnel lining structure and the development of plastic zone in surrounding rock are obtained,the stability of tunnel is evaluated,and the safe distance between tunnel and concealed karst cave is further determined.Combined with the theoretical analysis results and engineering practice,the treatment measures for hidden karst caves are put forward.