Prediction Of Deformation And Of Optimum Supporting Time For Tunnel With Horizontal Layered Surrounding Rock

For the current researches for the interaction between the rock and the support,the surrounding rock is commonly assumed as isotropic.However,the layered surrounding rocks are widely distributed in different areas where the mountain tunnels are excavated.The layered surrounding is assumed as anisotropic.Therefore,it is of critical significance to analyze the rock deformation and the optimum preliminary supporting time of the tunnels that is excavated in the layered surrounding rock.In this thesis,according to a practical tunnel case in Yongguang,by the finite difference software FLAC3 D,the 2D and 3D numerical models for the tunnel surrounding the horizontal layered rock are established based on the ubiquitous joint constitutive model.Two analysis methods of the optimum supporting time for the 2D and 3D models are determined and verified.The main contents and conclusions are as follows:(1)According to the practical engineering,3D tunnel numerical models are established by FLAC3 D.Based on the ubiquitous joint constitutive model,the rock deformation at the tunnel periphery,the distribution of the plastic zone,the stress distribution of the rock with different joint frictions and joint cohesions are analyzed.(2)Based on 3D numerical tunnel models,the maximum rock deformation on the vault and the maximum stress in the preliminary support are analyzed with different supporting times(supporting time is represented by the distance from the excavation face to the location where the preliminary support is installed).By the calculation results,the optimum supporting time is determined and the longitudinal deformation profile(LDP)for the tunnel vault is analyzed.(3)A more simplified method of 2D method is proposed to investigate the optimum supporting time for the preliminary support.Based on the 2D numerical tunnel models,through the reverse stress method,corresponding to different relief factors of the stress,the relief factors of the displacement at the tunnel vault are obtained,the variation of the relief factors of the stress versus relief factors of the displacement is established;meanwhile,theplastic zone in the rock and the increment of the rock displacement at the tunnel vault are determined.According to the plastic zones and increments of the rock displacement,the optimum relief factor of the stress is gained.Combining the variation of the relief factors of the stress versus relief factors of the displacement with the LDPs,correlation between the relief factor of the stress and supporting time is obtained.Combining this correlation with the optimum relief factor of the stress,the optimum supporting time calculated by the 2D model can be solved.