Study On Stability Of The Vi-class Surrounding Rock Of Large-span Shallow Tunnel Under Unsymmetrical Pressure

The Liangcun tunnel in Gan Shao railway were the main researching causes in this paper.According to the CRD method in the construction of liangcun tunnel,the process of tunnel excavation is simulated and the stability of surrounding rock and supporting structure is analyzed.Through the monitoring measurement technology, the stability of surrounding rock is studying in the shallow tunnel,sustained unsymmetrical pressure in the VI-class surrounding rock.Combined with the research of the tunnel at home and abroad and present situation of the methods,in the tunnel excavated by CRD method,the stability of surrounding rock and supporting structure is for a more in-depth research work in this paper.First,by using the finite element program with MIDAS/GTS,the process of CRD and Three-bench Seven-step excavation is analyzed by 2D simulation respectively, through calculation of two kinds of different construction methods,the deformation and force of surrounding rock and the stress and internal force of supporting structure is compared.From the angle of the structural deformation and stress,the CRD excavation is more reasonable.Then,based on CRD method,shallow tunnel sustained unsymmetrical pressure have different excavation,Is the outside tunnel's excavation should be first or the insider tunnel's excavation should be first? according to these two kind of tunnel excavation orders,the displacement and interal force of tunnel structure are analyzed by building the 3D-model of the liangcun tunnel with MIDAS/GTS.according to these two kind of tunnel excavation construction orders on a 3D model and process of tunnel structure of the displacement field and stress field are analysed,it is concluded that the deformation and force is smaller in the order of the tunnel excavation that the outside tunnel's excavation is first.so the method of this excavation order is more effective.Finally,through the tunnel monitoring results of the tunnel,It can obtain the ground surface settlement curve,the arch crown subsidence curve,Variation curve of horizontal convergence,Surrounding rock pressure curve,the axial force on the steel brace curve and so on.Then compared monitoring results with the theoretical calculation and verified each other.The structure internal force monitoring results indicated that the axial force on the steel brace were pressure force and the axial force at hance were larger than other position's.The surveying analysis suggest that the reasonable construction for the shallow tunnel should be:the outside tunnel's excavation and preliminary lining should be first,and then the insider tunnel's. the order of the tunnel excavation that the outside tunnel's CRD excavation is more reasonable.Through the tunnel monitoring results of the tunnel,it can get the information feedback of deformation and force of the surrounding rock,guide the construction of tunnel and modify the design parameters of surrounding rock.On the basis of preliminary judgment for the ability of surrounding rock stability,in combination with the numerical Simulation,it can get a more accurate information of tunnel structure,it is very useful for the design and construction of the tunnel.