Mechanism Of Pipe-roof In Shallow-buried Tunnels And 3D Numerical Simulation Of Construction Procession

With the rapid development of urban infrastructure construction, shallow mining method is widely applied in underground projects such as metros, underground streets. However, the theoretical study is far behind engineering practice.Taking a project in Tianjin as the background, the mechanisms of pipe-roof pre-support and leading conduit pre-reinforce in shallow tunnels were analyzed by using theoretical analysis, numerical simulation and other research tools. And the whole construction procession of shallow tunnel was also simulated. Research obtained the following results:(1)Pipe roofs used to restrict the soil deformation, leading conduit pre-reinforcement and core soils used to maintain the tunnel face stability are very important to control the ground settlement, to reduce the impact on the surrounding environment and to provide the security for the construction work.(2)The calculated results show that pipe roofs, elastic modulus, Poisson's ratio and the length of reinforcement can partly affect the ground settlement and the surface subsidence. It also indicates that the function of reinforcement can be taken into account by changing the elastic modulus and the Poisson's ratio during the analysis. Pipe-roof support can restrain ground deformation and the leading conduit improves the stability of tunnel face, which makes the tunnel excavation process safer.(3)The tunnel construction procession is simulated. The development of surface subsidence, ground settlement, plastic zones and the force of pipe-roofs and tunnel initial support were analyzed, which verified that pipe-roof pre-support and leading conduit pre-reinforce in shallow tunnels can meet the requirements of ground deformation.The conclusions in this paper can give construction guidance for the actual project and also be referred by other similar projects.