Study On Construction Stability Of The Subway Station Tunnel With Shallow Buried Super Large Section

The paper took Guanshui Metro Station on Guiyang Metro Line 2 as the research background.Theoretical analysis,finite element simulation and field measurement were combined to explore the dynamic changes of the pressure arch of the pits of both side heading method under the action of unloading in the shallow buried super large section tunnel construction.The results were used to improve the design and calculation method of the existing surrounding rock pressure processes.Based on the understanding the dynamic changes of the pressure arch in excavation for large section tunnel,from the perspective of surface subsidence,support and surrounding rock stress state and plastic zone of surrounding rock,the finite element simulation and on-site monitoring methods were adopted to analyze the construction mechanics of construction method of single-span super-large section tunnel and conversion construction plans between the auxiliary tunnel and large-section tunnel.Based on the results of numerical simulation,a safe and feasible construction plan was determined.The main research work was as follows:(1)Based on the commonly used methods for defining the size of tunnels and the definition of deep and shallow tunnels,the characteristics of the tunnel excavation of Guanshui station tunnel were analyzed and defined.What's more,based on the characteristics of shallow-buried super-large section tunnel and the strata of the Guanshui tunnel,from the perspective of construction technology,the features and adaptability of the bench method with reserve core soil method,double side driftmethod,CRD method and the single-arch method were analyzed;the construction characteristics of the expansion excavation method of fan type conversion,climbing method of door type conversion and double holes excavation with rock pillar were studied.The above studies provided preliminary suggestions for the numerical simulation to determine the construction plan for shallow-buried super-large section tunnel.(2)The main construction and the stress variation characteristics of surrounding rock of shallow-buried super-large section tunnel under different surrounding rock levels were analyzed.Depending on the process load method,(the structure-load calculation method with the influence of the construction process),the change of the physical and mechanical parameters of the surrounding rock during the large section tunnel excavation was considered.The unloading effect was introduced to analyze the change of surrounding rock pressure of Guanshui station tunnel under the double side drift method,which could identify the changes of the outer boundary of the pressure arch and determine the load variation range of the surrounding rock.The results provided basic data for the design of Guanshui station tunnel.(3)Finite element simulation was conducted on the dynamic construction mechanics of shallow-buried large-section tunnel during the construction under the bench method with reserve core soil method,double side drift method,CRD method and the single-arch method.The deformation and stress characteristics of surrounding rock and supporting structure under different construction method,and the changes of strata settlement and surrounding rock plastic zone caused by those methods were analyzed.The research results suggested that the double side drift method should be adopted in the construction of Guanshui station tunnel.(4)Based on the construction of shallow-buried super-large section tunnel under the double side drift method,the three construction methods between the auxiliary tunnel and large section tunnel,fan type conversion,climbing method of door type conversion and double holes excavation with rock pillar were studied,were studied by numerical simulation.The sress and deformation of the surrounding rock-support structure system were further analyzed,and the “double holes excavation with rock pillar” method was determined.The on-site monitoring was conducted and themonitoring data showed that the “double holes excavation with rock pillar” method can be better used in the control of the change of the surrounding rock stress and deformation.