Study On Construction Method Optimization For Entrance Section Of Neighborhood Tunnel Throughing Fractured Fault Zone

With the continuous advancement of China's economic construction,a large number of tunnel projects have emerged.With the advantages of flexible net distance,simple construction technology and convenient cost control,the neighborhood tunnel has been widely used in the construction of mountain tunnel.Due to shallow buried depth and broken rock mass in the entrance section of the tunnel,a slight carelessness in the construction process may cause slope instability and other engineering disasters.When there is a fault in the vicinity of the entrance section,the geological conditions of the tunnel entrance section will be more complex,this makes excavation more difficult,the technical requirements more stringent.At this time,the selection of which construction combination scheme for tunnel excavation directly affects the stability of surrounding rock.A scientific and reasonable construction scheme can not only give full play to the self-supporting capacity of surrounding rock,but also shorten the construction period and save the cost.At the same time,it is very important to choose the scientific pre-strengthening method which is suitable for the construction method.In view of the above problems,this paper relies on the DAPINGWEI tunnel engineering in CangNan county,Zhejiang province,and uses the finite difference software to systematic study.Main research contents are as follows:(1)Based on the field monitoring data,focusing on the analysis of the vertical displacement and horizontal displacement change rule of the tunnel entrance section,use the displacement change rate and displacement change acceleration as the main evaluation basis to judge the feasibility and scientificity of the project's excavation plan.(2)The finite difference software FLAC3D is adopted to simulate neighborhood tunnel entrance section of shallow buried excavation,design different excavation combination plan for left and right hole,analysis the effect on the stability of surrounding rock excavation scheme,obtain the optimal scheme of excavation.(3)On the basis of optimizing the tunneling scheme and adopting the method of fixed parameters,the influence of different piperoof parameters on the stability of surrounding rock of the tunnel was discussed respectively.Considering the effect of pre-reinforcement,the feasibility of eonstruction and the eost of the project,a relatively reasonable parameter range of piperoof is put forward.In this paper,the advanced numerical calculation method and analysis method are used to study the construction method of crossing the fault fracture zone in the shallow entrance section of neighborhood tunnel and the optimization of piperoof parameter,which have high engineering application value and provide reference for similar practical projects in the future.