| Mountain tunnels are a common form of tunnels in tunnel engineering.Due to the complex geological structure and the impact of dangerous rockfalls,fault fracture zone and other adverse geological structures,a series of problems have been encountered in the construction process.This paper takes the double track railway tunnel built in the mountain as an example.The total length of the tunnel is 3596m.The stratum lithology is mainly quartz sandstone,locally mixed with siltstone and meta sandstone with siltstone.The surrounding rock is broken.The tunnel construction is difficult and the construction risk is high.There is a translational fault and a fold belt in the site selection area of the tunnel.The rock mass of the fault zone is broken and the roof of the tunnel is easy to collapse.The section DK99+590?DK100+790 of the side wall of the tunnel is a high ground stress area,and rock burst may occur during excavation.Aiming at these problems,this paper studies the following contents(1)Bad geological structures such as faults,folds and faults occur in the site selection area of the tunnel.The top of the cave is easy to collapse,the grade of surrounding rock varies greatly,it is necessary to use pipe shed for advance support or grouting reinforcement to ensure the safety of the excavation face.(2)China adopts a wider tunnel wall rock pressure calculation method is to calculate the tunnel loose load,according to different tunnel burial depth to adopt the corresponding calculation formula and lateral pressure coefficient.And the maximum load is selected as the design basis.(3)According to the measured data from the trial excavation of the tunnel,the range of the tunnel loosening ring ranges from 0.5 to 2.8m.The maximum axial force located at the arch foot,and the maximum bending moment located at the arch waist of the tunnel,the calculation results are within the bearing resistance of the secondary lining.(4)The in-situ stress level and geological environment of Liucheng Tunnel determine that the horizontal displacement is greater than the vertical displacement.When the arching effect of the anchor cable support is obvious,the surrounding rock stress structure changes and the load When the force is increased,the deformation of the bottom plate becomes smaller,which can fully exert the reinforcement of the anchor to form an arch as well as the suspension effect of anchor cables,they work together to control the deformation of surrounding rocks and improve the stress structure.Combining the engineering geological conditions of this project with the requirements of railway tunnel construction,using a combination of geological survey,theoretical analysis and numerical simulation,the construction technology and supporting parameters are selected reasonably,so that the tunnel design is safe,practical,reliable and economical.3.Advanced technical requirements to achieve reasonable control of tunnel deformation,surrounding rock stability,guarantee construction safety and keep trafic smooth.The FLAC3D system was used to study the effect of supporting parameters on controlling surrounding rock deformation,and it is expected to provide reference for the same type of tunnel.And made relevant research results. |
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