Abstract: To investigate the mechanical properties of rocks under dynamic shear load, experiments were conducted on cubic granite specimens under different normal stresses and impact velocities using the impact-induced direct shear method. The dynamic shear deformation evolution process of granite was analyzed, and the effects of normal stress and impact velocity on shear deformation and failure patterns of granite were discussed. Subsequently, the impact-induced direct shear experiments of granite were simulated using particle flow code. The evolution mechanism of shear deformation and damage was further explored from a microscopic perspective. The results show that the normal stress varies continuously during the shear deformation of the specimen, and the normal stress corresponding to the peak shear stress can reach several times the initial value. Two types of shear stress-shear displacement curves, rebound-type and fracture-type, were obtained. With an increase in initial normal stress, the peak shear stress increases while the peak shear displacement and maximum shear displacement decrease; with an increase in impact velocity, both peak shear stress and maximum shear displacement increase. Fractures in granite specimens contain a main fracture and multiple wing cracks. As normal stress and impact velocity increase, the main fracture profile becomes flat from wavy, and the fracture surface becomes smooth from rough, possibly due to frictional slip. The initiation fracture of granite specimens originates from the interior and then extends to the boundary along the shear direction. The direction of fracture initiation is oblique to the shear direction, consistent with the inclination of the contact force concentration zone. The experimental method used in this study provides a reference for testing dynamic shear mechanical properties, and the findings can help reveal the mechanism of dynamic engineering disasters induced by shear fracture of rocks.

Key words: dynamic shear, granite, impact-induced direct shear experiment, particle flow code, shear fracture