Study on the influence of fracture geometry characteristics on the shear behaviors of fractured rock mass

Abstract The shear behavior of fractured rock masses critically influences engineering stability, particularly in slope engineering. Overcoming limitations of conventional preparation methods, this study utilizes sand-powder 3D printing to fabricate rock-like specimens with controlled internal fractures. Direct shear tests systematically investigate fracture radius and number effects on strength evolution under constant density, with quantitative analysis revealing their differential contributions. The results show that: (1) The failure of sand-powder 3D-printed fractured rock-like specimens exhibits brittle characteristics. The shear stress–shear displacement relationship can be divided into five stages: compaction, elasticity, unstable development, peak, and post-peak. Crack initiation and propagation primarily occur from the late elastic stage to the peak stage. (2) An increase in fracture radius significantly reduces pre-peak shear stiffness, resulting in a smoother curve progression, while changes in fracture number have minimal impact on the stage-specific characteristics of the shear curve. (3) Shear strength decreases exponentially with increasing fracture radius, whereas an increase in fracture number leads to a linear reduction in shear strength. Moreover, the weakening effect of fracture number on shear strength becomes more pronounced with larger fracture radius. (4) Quantitative analysis shows that the influence of fracture radius on shear strength is 2.4 times greater than that of fracture number. This study broadens the understanding of the shear behaviors of fractured rock masses and reveals the key influence mechanism of fracture density on rock mass deformation and failure, and provides theoretical guidance for slope stability analysis and rock mass engineering design.