Shear mechanical properties of loaded rock under drilling and dynamic load and its influence on the plastic zone of roadway

• Shear strength of drilled rock decreases linearly with increasing borehole diameter. • Cohesion first increases then decreases with higher pre-static load and dynamic load amplitude, while internal friction angle consistently decreases. • Shear failure surface transitions from rough to smooth due to static load enhancing tooth cutting and dynamic load causing repeated crack friction. • Borehole pressure relief enlarges the plastic zone radius of surrounding rock following a quadratic function, informing support design.