| In view of the weak and broken surrounding rock at the top of luojiashan tunnel of zhengwan high-speed railway,poor self-stability and complex geological structure,large deformation caused by extrusion occurred many times in the construction,resulting in cracking of primary branch,distortion of steel frame,and breaking and replacing of primary branch.Based on the monitoring data and the lithological characteristics of carbonaceous shale,the deformation of surrounding rock and the stress law of supporting structure of soft rock tunnel are analyzed.The finite element analysis method is used to simulate the deformation of surrounding rock and the change of internal support force caused by different construction excavation support measures,and the best construction measures are selected through comparative analysis.The main research contents and results of this paper are as follows:(1)Based on the analysis of the existing support methods and their interaction mechanism,the influence of various main factors on tunnel deformation is analyzed,and the mechanical mechanism and deformation characteristics of soft rock tunnel instability are studied.(2)The monitoring results and engineering geological data show that the surrounding rock at the top of luojiashan tunnel is carbonaceous shale,and its deformation characteristics are greatly affected by the strength of the surrounding rock and the tendency of rock strata.After tunnel excavation,the deformation speed is fast and the duration is long,which reflects the remarkable rheological characteristics of carbonaceous shale.(3)MADIS/GTS is used to simulate the cross section between the flat guide and main tunnel of Luojiashan Tunnel.The deformation of surrounding rock and the stress law of initial support of soft rock tunnels such as carbonaceous shale are studied.Assuming different deformation control measures,such as controlling the type of steel arch,the size of roof overhang and the excavation footage,the deformation and support of surrounding rock under different support parameters,different structural characteristics and different excavation methods are analyzed.Through comparative analysis,the optimum excavation method and support parameters are selected..(4)Through the analysis of all kinds of construction scheme of the numerical simulation results,considering the deformation of surrounding rock control effect and construction schedule and project cost factors,using pick up against the door frame outside carry length of 0.8 m,excavation is set to three times the steel arch span is about 1.8 m,to 30 cm,early bolting spray thickness combination of site construction steel arch support for optimal construction scheme.The research results of this paper have been successfully applied in the construction of luojiashan tunnel of zheng-wan high-speed railway,and good results have been achieved.The research results can provide technical reference for similar projects. |
