Stability Study On Surrounding Rock Of Neighborhood Tunnel With Large Span

With the fast development of highway, the number and style of tunnel also showing the trend of rapid growth, neighbothood tunnel with large span represents the direction of the development of a highway tunnel. Neighborhood tunnel with large span can increase the road capacity and overcome the engineering site constraints, and many other advantages, But its structure determines that its construction is very difficult and security risk is very high. This paper will based on Niutoushan tunnel Humen Town,Dongguan.to study the stability of surrounding rock of two-way eight-lane tunnel with small spacing.Based on elastic-plastic mechanics, to analyse the initial field rock stress, the surrounding rock stress of circular tunnel, and the radius of plastic zone, to study the action of rock stress after tunnel excavation,and more,introduced the double-shear theory, to derive the radius of plastic zone and displacement of surrounding rock under the affection of intermediate principal stress. Combined with monitoring and test data of Niutoushan tunnel, to analyze the displacement and force supporting structure of tunnel key parts,the results show that it should focus on strengthening support of middle rock column and arch waist in the process of construction.Established difference finite model of neighbothood tunnel with large span, under the bench method, twin side method and single side method,and calculated the middle rock column distribution conditions of force and plastic zone. Analysis showed that twin side method to control the surrounding rock displacement and protection the stability of middle rock column is more favorable underⅤ-class surrounding rock.Established no supporting tunnel model, to analyse the minimum reasonable space inⅤ-class surrounding rock by the criterion of plastic zone through, but in theⅣ-class surrounding rock, the criterion of no supporting tunnel minimum reasonable space is yield approach index.and more, established model of supporting tunnel, analyse its minimum reasonable space inⅤ-class surrounding rock.Simulation the process of excavation cycle by three-dimensional model under different construction space, to analyse the changes law of stress and strain. Results show that the excavation impact depth to the cross-section is mainly in the area of one times tunnel space,so tow tunnels keeping two times tunnel space is more reasonable.This paper summarizes the conculation results and the law of rock changes under the tunnel construction process,according to these results,focused on the temporary tunnel design distance and construction method,we take an optimizing adjustment.