Analysis of Mechanical Properties and Instability Influencing Factors of X-shaped Jointed Rock Mass

This study delves into the mechanical behavior and fracture propagation mechanism of X-shaped jointed rock masses. It is found that the damage of X-joints leads to stress concentration at the joint tips, which promotes the propagation of fractures along the direction of the maximum principal tensile stress, eventually causing the rock mass to fail along the joint surfaces or at an angle of . Under the influence of X-shaped joints, shear fractures in the rock mass increase rapidly in the initial stage of loading and then transform into tensile fractures. These tensile fractures continue to propagate and coalesce into a connected fracture network, significantly weakening the structural integrity and mechanical strength of the rock mass. The uniaxial compressive strength of X-shaped jointed rock masses shows a negative correlation with the length of secondary joints. An increase in the length of secondary joints actually expands the initial damage area in the rock mass and exacerbates the tip stress concentration effect, thereby reducing the overall bearing stiffness and strength of the rock mass. With the increase of the included angle between primary and secondary joints, the compressive strength exhibits a nearly "M-shaped" variation, reflecting the anisotropic influence of the spatial geometric configuration of joints on rock mass strength. Regarding the included angle between the primary joints and the loading direction, within the range of , the rock mass strength increases slowly with the increase of ; while within the range of , the strength decreases rapidly with the increase of . The research findings deepen the understanding of the failure mechanism of jointed rock masses and provide a theoretical basis for engineering site selection and disaster reduction decision-making.