Study On Excavation Method Of Reserved T-type Rock Pillar In Large Section Tunnel Of Subway Station

The development of rail transit construction technology is changing with each passing day,which makes the planning of the rail transit route become a reality,it also makes the rail transit lines cross each other,overlap or parallel,large cross-section of the station or line came into being.Large cross-section rail transit stations are mostly located in the center of the city,where the surrounding buildings,facilities and equipment are numerous and complicated.However,in the domestic research on the excavation method of ultra-large section rail transit tunnel is not very mature.The maximum excavation section of the main part of the xiazibian subway station of Chongqing Rail Transit Line 4 is 28.47m(H)×26.72m(W),whose excavation area is up to 670.31m2.In this paper,the research on the excavation method of T-type rock beam is carried out relying on xiazibian subway station.The main contents and conclusions are as follows:①The construction examples and research literatures of large cross-section tunnels at home and abroad are collected,and the characteristics of each project are compared on this basis,and the advantages and disadvantages of various excavation methods are summarized.② Aiming at the construction methods of various common large-section tunnels,the double side drift construction method and reserved cross rock beam-pillar method are proposed as the comparative construction scheme of reserved T-rock pillar method,which are suitable for excavation of large section tunnel.③ The finite element software MIDAS GTS NX is used to simulate and analyze,and the simulation results of tunnel construction under three kinds of processes are compared and analyzed.The characteristics of each method are summarized as follows:1)During the construction process,the settlement value of the tunnel vault can be effectively controlled,and the settlement value of 10.21mm will be produced by using the cross-type rock beam method.The settlement value of the double-side-drift method is the smallest.The settlement value of the surrounding vaults produced by the reserved T-rock pillar method is between the two values.2)When the double-side-drift method is used for tunnel construction,the maximum convergence deformadon value is obtained,the maximum value reaches 18.76mm,However,the reserved T-rock pillar method has the lowest value of 3.72mm,which indicates that the reserved T-rock pillar method can effectively control the convergence of tunnel rock.3)The results show that the surface subsidence value of the reserved T-rock pillar method is lower than that of the double-side-drift method or the reserved cross-rock pillar method,and the final cumulative sedimentation value is 4.44mm.4)By comparing the bending moments of the initial support,the results show that the reserved T-rock pillar method can effectively reduce the bending moment during the excavation period,which can improve the safety factor of tunnel construction.The results show that the reserved T-rock pillar method is more suitable for the construction of large-section tunne under the Ⅳ-level surrounding rock 1.The research results have certain reference value for xiazibian tunnel and similar project.