Stability analysis on soft and weak surrounding rock of diversion tunnel in high geostress zone

Taking the construction of deeply buried diversion tunnel as the study background,the distribution characteristics of the peripheral displacement,surrounding rock deformation and time-dependant development law of supporting stress are studied in combination with the relevant lab-experiment,numerical simulation,measured data of monitoring on construction deformation and in situ test on surrounding rock-lining contact pressure based on the understanding of the property of surrounding rock pressure that causes large deformation and the analysis on the mechanical behavior concerned. The study result shows that( 1) within the environment of the high geo-stress with the major principal stress in a vertical direction,the larger deformation of soft rock is mainly the extrusion deformation;( 2) the excavating face and the secondary lining play important roles on constraining the spatial displacement distribution of tunnel;( 3) the development of soft surrounding rock deformation and the supporting stress have obvious rheological behaviors and time effects,and then placing the secondary lining can effectively restrict the development of the rheological deformation. On the basis of this study,some suggestions favorable to control the surrounding rock stability during construction are finally proposed as well.