Shallow Bias Tunnel Construction Technology Research Into The Hole

There are many geologic and construction problems encountered in the construction of tunnel entrance in the shallow-buried and biased-pressure area of mountainous area.Mainly displays in the mouth of the cave surrounding rock generally more broken,easy to weathering,poor stability of surrounding rock mountain slope surface,can cause the stress of surrounding rock after excavation damage,and collapse,the hole construction has impressed by many external factors,engineering footage to bring huge difficulties.In this paper,based on force can rely on highway FengYan tunnel engineering,expounds the features of the shallow bias tunnel project,using the finite element numerical simulation method to the mouth of the cave side slope stability and the construction of the key process of arch pipe roof bolting system has carried on the simulation research and analysis,and combined with field monitoring measurement the safety and reliability of the engineering construction were analyzed.The main research works and achievements are as follows:(1)It is necessary to understand the engineering characteristics and stress characteristics of shallow-buried and biased-pressure tunnels in shallow-buried,biased-pressure tunnels.Therefore,the stress characteristics and deformation laws of shallow tunnel and biased tunnel are studied respectively.It is concluded that the core of the phenomenon is the balance of the earth pressure on both sides of the tunnel.The main techniques include setting retaining wall,backfilling heavy soil,excavating the soil to reduce pressure,and pre-grouting to reinforce the surface of the tunnel.(2)The surrounding rock is easy to be broken and weathered joint development,in the process of tunnel portal construction is easy to affect the mountain rock mass balance,three steps of seven,CD,pilot tunnel method in advance construction methods such as comparative analysis,it is concluded that the three steps seven method has quick construction efficiency,suitable for large mechanical construction,the construction security is higher,the excavation technology difficulty is moderate,the surrounding rock stability constraints have maintained good,its auxiliary process construction advantages,Therefore,three-step excavation method is selected as the construction scheme.(3)The slope stability of the tunnel entrance is easily affected by the groundwater,geological characteristics of the surrounding rock and the structure,construction factors.The finite element simulation software is used to analyze the stability of the tunnel entrance slope to determine the stress characteristics of the tunnel entrance and the safety status of the support structure.Numerical simulation study of slope excavation of the plastic zone is small,the pressure can solve through back fill,ensure safety;Vertical displacement from the side slope to excavation,in turn,reduce the slope foot,seen in displacement vector diagram,displacement change large area is located in the level in the upper slope,slope deformation trend for slope slide.Mouth of the maximum compressive stress is 1.07 Mpa,the biggest located at the base of the anchor rod,anchor axial force is 2.29 Mpa,tunnel and the stability coefficient is 1.98,meet the design specification requirements.(4)According to the FEM numerical simulation analysis of the safety of the arch surround and pipe shed which are the key control step in the initial stage construction of the tunnel,the maximum compressive stress is 2.29 MPa on the inner side of the arch,which occurs at the right shoulder of the tunnel.Under the common actions of the mountain thrust and self-gravity,biased wall has the left around side of the wall of the ear wall rotation trend.The maximum deformation vector of the bias wall is 1.05 mm,the maximum angle of rotation around the Z axis is 1.39 × 10-4 radian,and the biasing pressure of the biasing wall is in the same direction.The overall deformation of the wall is small and its structure is stable.(5)To master the surrounding rock deformation convergence and stability of the support structure has important significance,during the monitoring and measurement in the construction of the tunnel.Especially for the section of the tunnel section vertical displacement monitoring,vault,left and right arch around the site Rock pressure and steel arch stress monitoring.The monitoring data can be used as both on-site stability analysis of the surrounding rock can optimize the construction parameters.