Uniaxial compressive rupture of X-fractured sandstone: Effect of intersection angle on crack evolution and failure mode via DIC

To elucidate the effects of fracture intersection angles on the mechanical behavior and rupture mechanism of X-fractured rocks, uniaxial compression tests were conducted on sandstone specimens with prefabricated X-fractures at intersection angles (α) of 30°, 45°, 60°, 75°, and 90°, coupled with full-field strain monitoring via Digital Image Correlation (DIC) technology. The results demonstrate that the compressive strength of X-fractured rocks is highly dependent on the fracture intersection angle, exhibiting a trend of first decreasing and then increasing with increasing α. Initial cracks consistently initiate at the lower-left tip of the prefabricated horizontal fracture and propagate in a clockwise direction. Further analysis of surface strain evolution reveals distinct failure patterns governed by the interplay of horizontal and shear strains: (1) Horizontal strain increases monotonically with axial stress until the rock reaches the failure stage, while the relationship between shear strain and horizontal strain is complex and strongly modulated by α. (2) When α = 30°, horizontal strain dominates, leading to a tension-shear mixed failure mode; for α = 45°, 60°, and 75°, shear strain exceeds horizontal strain, resulting in pure shear failure; when α = 90°, horizontal strain becomes predominant again, inducing cleavage (tensile) failure. This study provides fundamental insights into the stress-induced deformation and failure of fractured rock masses, offering a theoretical basis for disaster prevention and control in rock engineering projects.