Research On Collapse Mechanism And Treatment Measures Of Tunnel In Gently Inclined Rockmass

The new localized railway Xuyong to Dacun is located in Xuyong and Gulin county territory, Sichuan province. Where is one of the thirteen major coal bases in Yunnan and Guizhou mining, the railway total length is 85.5 km. Xuda railway is currently planning the only resourceful railway line contact Luzhou and mining of Guxu. The tunnel of Zhengfengsi is 7336 meters length, which entrance is located in Shiping town of the Gulin county, the middle of tunnel is located in Ziqiang town of the Gulin county, the tunnel exit is located in Dongxing town of the Gulin county, the maximal depth of tunnel is 348 meters. The vault of tunnel appeared off the block when working on the tunnel face in DK78 + 265, collapse section continues to expand after the vault destruction. The initial supporter of tunnel affected by Collapse have cracked and deformed in DK78 + 180~DK78+225. this paper is based on the collapse disaster of Zhengfengsi tunnel in Xuda railway for the study. By geological analysis, physical simulation and numerical simulation, and by in-depth systematic study on the deformation response of the collapse and surrounding rock stability, on this basis, choosing a reasonable and effective advance support program, and making evaluations on the supportive effect. Through a comprehensive system of analysis and assessment, this paper made the following contents and achievements:(1)According to preliminary geological survey data, and combined with the field investigation of the geological conditions and the review during excavation,we studied the structural characteristics of the section of tunnel collapse section, the results show that the section of tunnel mainly developed shale which thickness between thin to Medium, some places can be founded thick-bedded Shale and limestone. Part of survey area shows a group of vertical joints, the other can not see joints. Study section inside the tunnel surrounding rock mainly has four kinds of deformation and failure mode :collapsed, sidewall drum, bass drum and chipping.(2)According to the sketches in the construction site, the structural characteristics of rock and the development characteristics of the preferred structural plane for the tunnel collapse are analyzed, And getting the tunnel surrounding rock classification during the construction. The results show that low connectivity between surrounding rock structural surface, low intensity and Structural plane space combination forming unstable blocks is the important reason for the collapse. On this basis, Establishing two kinds of geomechanical models for tunnel collapse by the perspective of the mechanical process: tension-bending and shearing, and Shear- slide.(3)According to the structure characteristics of rock, using the experiment of basal contact friction in physical simulation methods, Simulating three cases for tunnel collapse, authors reappear the whole process of occurred and developed on tunnel collapse, then Summarizing of deformation and failure characteristics of each different models: thin ~ in thick bedded surrounding rock deformation and failure include built-in beam bending shear failure, bending beam damage and the rock layer alienation three process, thick bedded surrounding rock deformation and failure of spandrel cantiever beam bending shear failure, joint rock tunnel surrounding rock is formed along the structural plane shear failure(4)Using UDEC and strength reduction method, analyzing of the changes under different strength reduction path for the roof surrounding displacement of tunnel, and discussing on the applicability of surrounding rock stability calculation determining indicators. Based on this, getting the overall safety factor of different sections of the tunnel collapse cross-section. Provide theoretical basis for the landslide section division and collapse treatment.(5)the longitudinal length is unknown for the section of collapse. According to the stability of the calculation results, we can divide the section of collapse by stability of tunnel, and Preliminarily determine the location of Collapse, thereby selecting a reasonable pre- timbering means to control tunnel collapse.(6)Combining with the feature of Zhengfengsi tunnel collapse and other similar experiences for collapse treatment, controlling the collapse by pipe roof and a small catheter tube. Monitoring settlements of roof surrounding rockmass and clearance convergence in the process of controlling the collapse and after the governance, Finally evaluating of the effect of collapse governance.