The Mountain Tunnel Seven-step Method Of Three-step Out Of Its Hole Construction Techniques And Risk Analysis

Currently many mountain tunnels were excavated form one portal to the orther portal. Reasonable tunnel construction scheme should consider surrounding rock steady, construction efficiency, engineering cost and other elements. This paper using the numerical analysis, risk analysis, and other means to research tunnel construction technology. The feasibility of three-steps-seven-footwork tunnelling method was put forward for tunnel unkennel construction, and were applicated in Xinjiaokou and Dalin tunnel. The main conclusions are as follows:1. The main characteristics of mountain tunnel portal section and the commonly construction method of tunnel portal were summarized. The differences of tunnel portal and various unkennel constrctions were discussed.2. Three-dimensional numerical analysis method was used to study the characteristics of deformation and stress of surrounding rock and supporting structure on the process of tunnel unkennel construction. The comparative analysis of three-steps-seven-footwork tunnelling method and small pilot tunnel method were performed.3. The rationality of three-steps-seven-footwork tunnelling method with exceed-ductile-routing auxiliary construction measures for tunnel unkennel construction in terrain difficult area was analysised. And their applications were performed in Xinjiaokou and Dalin tunnel.4. Construction risk analysis was performed for tunnel unkennel construction with the method of three-steps-seven-footwork tunnelling in Xinjiaokou tunnel. By enumerating the risk source in tunnel unkennel construction process, the analytic hierarchy process and fuzzy comprehensive evaluation methods were used to evaluate instability risk of tunnel portal. And the corresponding risk control countermeasures were proposed.