Study On The Safety Thickness And Construction Scheme Optimization Of Energy Release Depressurization And Outburst Prevention Layer In Karst Tunnel

Karst areas usually contain many high-pressure water-filled caves,and when tunnels are built,they are prone to water inrush disasters,resulting in property damage and even casualties.In this paper,based on the Xinjie Tunnel of Kaili Expressway in Guizhou Province,the influence of the energy relief and pressure reduction method on the surrounding rock of the tunnel is studied by combining theoretical analysis and numerical simulation,and the optimization of the energy release pressure reduction method is carried out,and the main research results are as follows:(1)In view of the condition that the cave is located directly in front of the face of the face,based on the calculation formula of the safety thickness of the anti-outburst layer of the complete face of the face of the rock wall,considering the deterioration effect of the decompression drilling on the rock mass,the finite difference software is used to simulate the unloading test of the rock mass,and the change law of the poisson’s ratio of the rock mass with the unloading quantity is obtained.Finally,based on the calculation formula of the safety thickness of the rock wall,the formula of the safety thickness of the rock wall under the condition of releasing energy depressurization is deduced.(2)Constraints water-eroded cave is located in the tunnel ahead of finite difference numerical model,simulation of the high pressure of rich water karst tunnel release can stepdown process,the results show that with the decrease of the karst water pressure,constraints in the rock wall of maximum tensile stress reduced 0.2 MPa,compressive stress reduced 2.5 MPa,most shows that interpretation can decompression can reduce the stress in the rock wall,increase the stability of the rock wall.(3)Constraints on the condition of the water filling cavity in front,considering the drainage hole of 9 kinds of different diameter,number and distance conditions,using the finite difference method under different working conditions,analysis of constraints of rock wall and surrounding rock stress and displacement change law of drainage hole aperture,drain hole size and layout of the drainage hole spacing on the influence law of surrounding rock;On this basis,the drainage hole construction scheme of the energy release and pressure reduction method of Xinjie tunnel was optimized.The optimized scheme was as follows: 11 drainage holes with20 cm holes were arranged in the middle of the face of the palm,and the drainage holes were arranged in plum shape with a spacing of 1m.Above the face of the palm,on the left side and on the right side,three drainage holes with 12 cm holes are arranged respectively.The drainage holes are arranged in a row with a spacing of 0.75 m.(4)Calculation scheme of optimization,and then compared with the front nine conditions,the results show that optimized condition constraints dike and the maximum principal stress of tunnel surrounding rock are much smaller than the other conditions,arch sedimentation of surrounding rock,the horizontal displacement and settlement of arch bottom arch waist is smaller than that of other conditions,explain condition compared with other conditions optimization,more conducive to the overall stability of surrounding rock.