Shallow Bias Neighborhood Tunnel Construction Scheme Optimization And Stability Analysis

With the rapid development of transportation industry in our country and green environmental protection, natural and harmonious design concept widely spread,neighborhood tunnel with its unique advantages was widely used in the construction of mountain highway tunnel. The geological condition was poor in neighborhood tunnel portal section. With the adverse effect of shallow buried and bias, the stability of surrounding rock ability was poor, convergence deformation was big after the excavation, will easily creat collapse and roof fall accident, the portal section was the control section in the tunnel construction. How to take economic and reasonable auxiliary measures of construction and excavation method, on the premise of ensuring the safety of construction, to reduce the shallow buried and the bias’ s adverse effects on the Tunnel stability was the key problems in design and construction of shallow bias neighborhood tunnel. This paper taked wenzhou cangnan county zaoxi tunnel as the engineering background, on the basis of refer to the related literature, in response to these problems were analyzed and studied systematically.（1）The bias tunnel treatment technology and the shallow buried tunnel excavation method was summarized in details. Introduced the theories of plastoelasticity and the basic knowledge of modeling in Flac^3D.（2）The numerical simulation software Flac^3D was used to research the influence of the stability of shallow bias neighborhood tunnel, by analysis the distribution of the surrounding rock displacement, stress and plastic zone of the tunnel in different thickness of back pressure revetment, the optimal thickness of back pressure revetment were obtained under the conditions of Ⅳ rock and Ⅴ rock, provide the reliable basis for optimization of construction scheme（3）By simulating the different excavation methods under the conditions of Ⅳ rock and Ⅴ rock and contrast the stability of the tunnel in the end, getted the reasonable excavation scheme.（4）By analyzing the change of displacement of the key points of the surrounding rock and the middle rocky column and the distribution of the stress concentration zone and plastic zone in the excavation process, understanded the tunnel in weak link in the process of construction and provided the basis for scientific guidance construction.Standing at the front of blast sciences, using the latest numerical calculation method, theoptimization of back pressure revetment thickness and tunnel excavation scheme was researched, which provides a validity measure for studying the stability of shallow bias neighborhood tunnel.