Study on the Influence of Crack Geometry Characteristics on Macroscopic Mechanical Properties of Roadway Surrounding Rock

Granite, although generally low in porosity, often contains numerous microcracks or microfractures that significantly constrain its mechanical strength. This study focuses on the mechanical properties of deteriorated rocks due to joints and cracks in granite, using the Mesozoic Sanjiazi granite in the Liaodong Uplift, Dandong City as a case study. A discrete element model based on particle flow was established using a trial-and-error approach to iteratively calibrate microscopic parameters until they matched actual conditions. Different fractured rock masses underwent uniaxial compression tests and orthogonal discrete element numerical simulations involving a 4-factor, 4-level experimental design. A multivariate linear regression analysis assessed the impact of the four factors on granite's mechanical properties, while numerical experiments investigated the influence of individual factors on its macroscopic mechanical characteristics. Results indicate that the geometric characteristics of cracks exert a greater influence on granite's peak strength than on its elastic modulus. Specifically, the sequence of crack geometric parameters affecting peak strength is crack Y-axis position component > crack X-axis position component > crack length > crack inclination angle. Similarly, the sequence of their impact on elastic modulus is crack X-axis position component > crack Y-axis position component > crack length > crack inclination angle. As the angle increases, the crack initiation point gradually moves towards both ends of the crack, with the specimen primarily experiencing tensile cracking and localized shear failure at the crack tips. Longer cracks correlate with lower peak strength and thus poorer stability in granite. Changes in the position of primary microcracks in granite significantly alter its peak strength and stress-strain state post-peak, albeit without a pronounced effect on elastic modulus. This research contributes valuable insights for predicting the mechanical properties of fractured granite.