The Mechanical Properties Research Of Shale Tunnel Excavation And Support

With the rapid development of China’s road transport, there is a lot of complicated geological conditions mountainous region in the Central and Western of China.In the process of building a tunnel to cross the geological conditions are often poor strata, shale formation is one of them. Because of the characteristics of shale which softening when receiving water often cause large deformation, collapse, a serious threat to the safety of staff and bring economic losses in the process of building a tunnel.The design and construction of Shale tunnel is a problem in recent years, therefore, it is necessary to study for practical engineering shale tunnel excavation and support process when the rock be softening in different conditions.This paper relies on the construction of a highway extension project named bojishan tunnel in Lucheng to Yuyang, Yichang city. According to the actual site design and construction methods adopted, combined with theoretical studies, field experiments and numerical simulation methods and ideas, and researching the tunnel surrounding rock and supporting structure.Analyzed by on-site real-time monitoring of deformation data, combined with the results of geological exploration tunnel,we find the law of mechanical parameters of shale rock after it be softening when it reaching water in the place, and the elastic modulus and cohesion are reduce, poisson’s ratio and internal friction angle increases, the ability to resist deformation of the surrounding rock be weaken. Shale tunnel deformation is large.The section of ZK55 +590 convergences 61.05 mm in the up step,and the down step convergence 3.50 mm,the dome settlement 33 mm. After the surrounding rock with water to soften, the tunnel deform become larger. The section of ZK55+610 convergences 287.60 mm in the up step,and the down step convergence 18.30 mm,the dom settlement 226.85 mm.The deformation rate increases with the rock softening,and gradually decreases after the release of surrounding rock stress.By numerical simulation analysis of the situation on-site, the deformation of surrounding rock is basically consistent with the experimental results when the rock with on water, and the on-site real-time monitoring of deformation data is larger than the calculate results when the rock be soften.Finding the displacement and stress field variation of surrounding rock and the deformation, stress distribution and internal force distribution of supporting lining in different time and different step when excavate the tunnel. After the surrounding rock with water to soften, because of the deformation of the tunnel, the bolt and surrounding rock occurred relative sliding,the bolt embedded in the tunnel. The largel deformation of tunnel is also the site of a large portion of the bolt force. And it also the place where the maximum relative sliding of bolt and surrounding rock. The numerical simulation results conform to the actual situation and the slipping anchor site.The force of bolt in the down side is symmetric distribution wih the up side of tunnel excavate disposablly,and it is not when the down side of tunnel excavate in mang times.The foce of bolt build at last is less than before,and we can consider applying for the mechanical effect of reduction of anchor.Through the study we found, the initial support of tunnel will be subsidence after the surrounding rock tunnel with water to soften,the settlement is gradually increased from the spandrel arch, and the vault settlement relatively less than spandrel settlement. Through analysis the stress of invert secondary lining when the surrounding rock be in soft,founding when excavating the tunnel after the surrounding rock softened,the tunnel is safety and stable when the down side of tunnel excavate disposablly,and the tunnel is safety when it in the operational phase no matter when the surrounding rock softened.