Shallow Buried Tunnel’s Pipe Roof Pre-reinforcement Theory And Its Upper Limit Research Under Variety Of Pre-reinforcement

In this paper, the main content is the stability analysis of shallow buried tunnel excavation face under the pre-timbering with tubular prop and variety of pre-reinforcement. Based on a2-d logarithmic spiral failure mechanism, and theorem of the upper bound of limit analysis, safety factor Fs is regarded as an index for evaluating the stability of tunnel excavation. A program wrote by Fortran language is used to calculate the upper limit solution of safety factor Fs under different working conditions, when surrounding rock was adopt pre-reinforcement. In Shenzhen Metro Phase six tenders for the engineering background, this paper analyzes the stability of tunnel face under variety of pre-reinforced way. Using the finite difference method to simulate the tunnel excavation face stability, getting the excavation methods and parameters which conducive to the stability of tunnel excavation face, and providing a reference for the optimization of tunnel construction methods. The main work of:(1) Basing on the Winkler elastic foundation beam theory to analyze the mechanical of pipe roof steel pipe, and using Fortran-program to design the pipe’s diameter, the tube length.(2) Building a2-d logarithmic spiral failure mechanism of shallow buried tunnel excavation face. Based on strength subtraction, nonlinear failure criterion of soil surrounding rock and tangent method, taking the upper limit of limit analysis method to derivate the expression of tunnel excavation surface safety factor Fs.(3) Calculating upper limit solution of safety factory by Fortran-program obtaining the upper limit solutions of under different working conditions, and analyzing the stability of tunnel excavation face.(4) In a variety of pre-reinforcement measures, the stability of tunnel face is studied. Meanwhile, this paper evaluates the tunnel face stability of the Shenzhen Metro project six tenders.(5) Using the finite difference method to analyze the excavation step distance, step length, length of core soil, obtaining their effects on the tunnel excavation face stability, providing a reference for the optimization of tunnel construction method.