Analysis Of Surrounding Rock Stability And Support Optimization Of Double-track High-speed Railway Tunnel Based On Large-scale Mechanical Construction

The rapid development of railway tunnel construction,mechanized engineering construction and tunnel construction technology level will gradually move to a new level,tunnel construction methods are changing towards mechanization,informatization,and intelligence.For double-track high-speed rail super-large section tunnels,traditionally,the excavation method is generally divided into sections.However,this method has a narrow excavation face,many construction conversion processes,and large construction machinery that is difficult to use,resulting in low excavation efficiency and project progress relatively slow.In recent years,with the continuous development of railway tunnel construction,a mechanized full-section construction method for double-track high-speed railway tunnels has emerged.Obviously,in the case of a large excavation area at one time,the analysis of the stability of the surrounding rock and the reasonable selection of supporting parameters are very important.Therefore,this article takes the Liuyuan tunnel project of the Huanghuang Railway as the research background,comprehensively uses analysis and research methods such as indoor test,field test,numerical calculation and monitoring measurement to analyze the stability of the surrounding rock after the mechanized full-section construction of the double-track high-speed rail tunnel.Carry out analysis,and optimize the support parameters for the typical construction mileage.The main content and research results are as follows:（1）Based on the strength reduction method,the BQ method of surrounding rock classification was revised,the cover span ratio was used as the influence factor of the surrounding rock classification,the tunnel surrounding rock classification cover span ratio correction coefficient K₄ was introduced,and the double-track high-speed rail tunnel was proposed to be below 100 m buried depth The value table of the cover span ratio correction coefficient K₄ for mechanized full-face excavation is applied to the surrounding rock section of the supporting project to verify the rationality of the cover span ratio correction[BQ]_H/Bmethod of surrounding rock classification,and achieved better results.（2）Considering the self-supporting capacity of the surrounding rock and taking the deflection of the principal stress trace above the tunnel vault as a sign of the formation of pressure arches,a numerical simulation study was carried out for the deep and shallow burial division of the double-track high-speed rail tunnel（excavation span 14.7m）,and the double The critical burial depth of railway tunnels under different surrounding rocks.（3）Determine the mechanical parameters of the quartz schist formation of the supporting project based on the indoor conventional triaxial compression test,and evaluate the stability of the surrounding rock in the mechanized full-section construction of the double-track high-speed railway tunnel based on the safety factor,and calculate the surrounding rock after the support.The safety factor is increased from 2.02 to 2.55 compared to the Maodong tunnel,which is an increase of 26.24%.（4）Using the method of numerical simulation and relying on the actual project,the initial support parameters of the double-track high-speed rail tunnel during the mechanized full-section construction are optimized.The results show that,under the premise of satisfying safety,when the tunnel is buried at a depth of 30m and the full-face excavation footage is 4m,the optimal support parameters are:initial support sprayed C30 concrete 20cm,I18 steel arch longitudinal arrangement spacing 2.0m,anchor length is 4.5m,and the circumferential direction×longitudinal spacing is 1.0×2.0m,which plays a guiding role for on-site construction.