Experimental Study on the Evolution Mechanism of Shear-Slip Rockburst Using a Rockburst-Prone Synthetic Material

To investigate the mechanical response and evolutionary mechanisms of shear-slip rockburst in fractured rock masses, intact, single-fracture, and double-fracture cubic specimens were fabricated using a self-developed synthetic material designed to reproduce pronounced elastic energy storage and rapid brittle failure. Shear-slip tests were conducted under normal stresses ranging from 0.9 to 3.6 MPa. The impact energy index, elastic energy index, and dynamic failure time of the material were 18.0, 9.2, and 140 ms, respectively. Shear stress, shear displacement, and normal displacement were monitored synchronously, while stress-drop events, shear-surface damage, and rock-powder mass were analyzed to clarify the controlling effects of normal stress and the fracture configuration. The results showed that, as the normal stress increased from 0.9 to 2.7 MPa, asperity interlocking along the shear surface was enhanced, resulting in overall increases in the peak and residual shear strengths and progressive suppression of dilation. At 3.6 MPa, all three specimen types exhibited pronounced stress drops, normal contraction, and complete loss of shear-bearing capacity, indicating a transition from stable frictional sliding to crushing collapse dominated brittle instability. The tested specimens suggest that increasing the number of prefabricated fractures may promote deformation localization and shorten the stable post-peak sliding process. At 3.6 MPa, the shear displacements corresponding to complete instability of the intact, single-fracture, and double-fracture specimens decreased from 9.0 to 7.8 and 6.5 mm, respectively, whereas the maximum stress drops increased from 0.28 to 0.62 and 0.90 MPa. These responses were characterized by earlier instability, increasingly concentrated stress-drop events, and larger individual stress drops. With increasing normal stress, the mass of rock powder increased from 11 to 56 g, indicating that shear surface damage evolved from localized fracturing to intensive crushing and grinding. The shear-slip process comprised four stages: compaction adjustment and load-bearing structure formation, elastic shearing and energy accumulation, damage accumulation and crack coalescence culminating in peak instability, and fragment reorganization with post-peak sliding. These findings provide experimental evidence for identifying shear-slip dynamic instability in fractured surrounding rock.