Analysis Of Unloading Deformation And Failure And Supporting Effect Of Non-persistent Jointed Surrounding Rock

Engineering rock mass is composed of structural planes and rock blocks.A large number of engineering practices have shown that the deformation and failure of engineering rock mass not only depend on the nature of the rock,but also mainly affected by the structural planes.Compared with other types of structural planes,the probability of joints existing in engineering rock mass is much higher.At present,underground engineering is generally built in complete rock mass or non-persistent jointed rock mass.The existence of non-persistent joints makes the stability,deformation characteristics and stress distribution of surrounding rock more complicated.The damage of the surrounding rock is often caused by the propagation and coalescence of cracks between the joints.Therefore,studying the deformation and failure of non-persistent jointed surrounding rock is of great significance to the practice of underground engineering.Based on the particle flow software PFC^2D,this paper used the method of"excavating after loading"to carry out related research.The research results provide certain guidance for further understanding of the deformation and failure of non-persistent jointed surrounding rock and support design after excavation.First,the calibration method of meso-parameters of the flat-joint model was studied,which lays the foundation for rapid and accurate calibration of meso-parameters and correct simulation analysis.Appropriate macro-and meso-parameters was chosen as experimental factors,and orthogonal design schemes was chosen to arrange numerical experiments.Then the fitting relationship between the macro-parameters and the main meso-parameters was determined through multi-factor analysis of variance and regression analysis,and the trend relationship between macro-and meso-parameters was analyzed.Finally,the meso-parameters calibration process of the flat-joint model was proposed,and the feasibility of this calibration process is verified.Secondly,numerical models of rock mass with non-persistent joints were established for excavation simulation,and the deformation and failure law of non-persistent jointed surrounding rock was analyzed from a mesoscopic perspective.The results show that the failure of non-persistent jointed surrounding rock is mainly caused by the coalescence between the macroscopic failure surface generated in the surrounding rock and the existing joints.The place where the joints and the boundary of hole intersect will have a larger displacement.The inclination and the continuity of non-persistent joints and the lateral pressure coefficient will affect the stress distribution,displacement distribution,failure mode,and the damage range and degree of the surrounding rock.When the inclination of non-persistent joints is small,the continuity of non-persistent joints is large,and the lateral pressure coefficient is small,the damage range of the surrounding rock is larger and more serious.Finally,with the diversion tunnel of Jinping II Hydropower Station as the engineering background,the engineering-scale excavation and support simulation was carried out.The supporting effect of Thin Spray-on Liners and concrete lining were analyzed and compared,and the mechanism of the new type of bolt shotcrete support and the impact of support timing were further discussed.The results show that the Thin Spray-on Liners basically cannot restrain the deformation and failure of the surrounding rock,but it can fix the spalled fragments in a suitable position and prevent them from falling into the tunnel.In the new type of bolt shotcrete support structure,the role of the bolt is to"support",and the role of Thin Spray-on Liners is to"protect".The degree of deformation and failure of surrounding rock decreases firstly and then increases with the lag of supporting timing.