| The subway parking line tunnel set between the left and right lines of the subway tunnel can effectively improve the efficiency of subway services and facilitate subway operation and management.In practice,the subway parking line tunnel has the characteristics of large span and multiple cross-section types,so there are problems such as frequent construction method conversion and large disturbance to the ground."Ensure the safety of the parking line tunnel structure itself and the safety of the surrounding environment" is the focus and difficulty of this type of tunnel construction.Based on the construction project of the parking line between Sanyuanqiao Station and Fangyuanli Station in Beijing Metro Line 12,this paper uses theoretical research,numerical simulation and field testing to analyze the construction mechanics of large-span complex subway parking line tunnels.The mechanism was studied.The main research conclusions are as follows:(1)There are many types of tunnels in this stop line,among which the length of the 5-5large-section tunnel is 297.7m,the span is 12.5m,and the covering depth is only 16.21 m,which is a typical shallow-buried large-span tunnel.Engineering practice shows that for ultra-shallow buried tunnels with a cover-span ratio of less than 1,the full-soil column method is mainly used to calculate the active surrounding rock pressure of the overlying strata.The cover-span ratio of the large-span tunnel of this project is between 1 and 1.5,and the subway design code does not specify the calculation method of the active surrounding rock pressure of this type of tunnel.At present,there is a big controversy about the pressure calculation of this type of tunnel.In order to explore the calculation method of the active surrounding rock pressure of this kind of tunnel,and provide the basis for the parameter design of the large-section tunnel support structure,this paper adopts the whole soil column method,the Xie Jiaxuan method,the principal stress axis rotation method and the stratum structure method to analyze the large-span tunnel The active surrounding rock pressure was calculated and analyzed.The calculation results show that the calculated values of the active surrounding rock pressure of the above four methods are324.22 kPa,289.7kPa,184.35 kPa and 126.12 kPa,respectively.Based on the comparative analysis of the calculation results,it is recommended to use the principal stress axis rotation method or the stratum structure method to calculate the active surrounding rock pressure of the shallow-buried and large-span tunnel of this project.(2)The large-section tunnel of the parking line of this project is located under the Capital Airport Expressway,with strict stratum settlement control and high environmental risks in the surrounding environment.This tunnel is excavated with multiple pilot tunnels.In order to reduce the impact of large-section tunnel excavation at the stop line on the surrounding stratum,this paper adopts numerical simulation for different grouting schemes,pilot tunnel excavation sequence schemes and pilot tunnel excavation footage schemes.Methods A comparative analysis of various schemes was carried out.The calculation results show that the tunnel’s advanced deep hole grouting layer thickness is 2.0m,and the pilot tunnel excavation sequence is "the pilot hole on both sides of the upper step-the middle pilot hole of the upper step-the pilot hole on both sides of the lower step-the middle pilot hole of the lower step" The construction plan with a pilot tunnel excavation footage of 5m has the best control effect on ground settlement.Therefore,this scheme is recommended as the excavation and support scheme for large-section tunnels on the parking line.(3)The large cross-section tunnel on the parking line is constructed by the double-side ditch method.The cross-section structure is complex,the construction sequence is multiple,the force system conversion is complex,and the temporary support removal causes multiple disturbances to the surrounding stratum of the tunnel.In order to explore a reasonable plan for dismantling bracing,three main influencing factors,including different dismantling sequence,dismantling length and whether to use bracing,are set up in different working conditions,and numerical simulation methods are used to compare and study them.The calculation results show that the temporary support plan for the jumping warehouse with a length of 8m to remove the support can effectively control the settlement of the ground without the use of support replacement.Therefore,this scheme is recommended as the construction scheme of the second lining of the large-section tunnel on the parking line.(4)In view of the multiple types of tunnels in the parking line between Sanyuanqiao Station and Fangyuanli Station,and the complex conversion of construction methods,the method of combining numerical simulation and on-site monitoring is used to focus on the construction of the spatial intersection of the parking line variable section tunnel.The mechanics mechanism was studied.The research results provide a basis for the setting of support parameters and the optimization of construction schemes. |
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