Optimal Analysis Of Construction Schemes And Monitoring For Shallow Buried Tunneling Of Rapid Transit Railway

For the aerodynamic effect, rapid transit railway tunnel usually have two-lane section with a single hole. The excavation area is generally up to 150 ~ 170 m2. Especially the technique difficulty and security risks of a shallow buried tunnel excavation is very obvious; therefore, it is very important to choose a reasonable excavation method for constructing the shallow buried tunnel.In this paper, a typical project is selected as the research object, which is Huajia Mountain two-lane tunnel of Nanqin railway in Guangxi. Based on the existing research results from domestic and foreign, by using the method of field research, theoretical analysis, numerical simulation, site test and so on, some key techniques are studied for constructing shallow buried tunnel of rapid transit railway. The research includes the rock deformation and the analysis of disruptive caused by tunnel excavation; the selection of construction schemes for shallow buried tunnel, which is based on numerical simulation; and site test studies. Among the mentioned above, the selection of Construction Schemes for shallow buried tunnel in Huajia Mountain is the focus of this paper. Through analysis, the main research results are as the following:(1) Based on the existing results, systematic analyses are made for the rock deformation and disruptive mode caused by tunnel excavation. According to the dynamic process of rock deformation, rock deformation of tunnel is divided into three parts, which are pre-displacement, face-displacement and displacement behind the tunnel face. The disruptive mode of rock is divided into six aspects. Based on the idea of that the tunnel excavation process is use and control of dynamic rock deformation (stress), the control techniques of rock deformation and disruptive are proposed.(2) Based on shallow sections of the tunnel in Huajia Mountain, two construction schemes are analysised by three-dimensional numerical simulation, which are CRD method and bench method with large arch springing. The results show that: CRD method is better than the other in the aspect of rock displacement and the distribution of plastic zone. The stress concentration of bench method with large arch springing is significantly reduced in the aspect of initial support structure force, the force of support is relatively reasonable. In addition, surface settlement caused by both methods can meet the current control standards.(3) Based on the result of numerical simulation, consider that the efficiency and safety of excavation and investment and other factors, the construction scheme of bench method with large arch springing is suggested for constructing the shallow sections of the tunnel in Huajia Mountain,(4) In order to verify the reliability of the theoretical analysis and numerical simulation, several projects are tested on-site, which are crown settlement, the level of convergence, surface subsidence, contact pressure between initial support and rock, axial force of bolt. The results show that: the measured data are basically consistent with numerical simulation results. It indicates that the numerical calculation and analysis are reliable. The proposed construction schemes base on theoretical analysis and numerical simulation is scientific and reasonable...