Study on Fracture Precursors and Crack Propagation of Rock under Different Gradient Stresses

Under long-term multiaxial stresses, rock masses exhibit gradient stress characteristics. Investigating fracture precursors and crack propagation under such conditions is crucial for monitoring and preventing rock engineering disasters. This study analyzed rock behavior using acoustic emission (AE) and digital image correlation (DIC) techniques under a gradient stress field. The findings indicate that as the gradient stress difference grows, rock strain decreases and the effective elastic modulus decreases. The load-displacement curve exhibits a dual-peak fluctuation pattern, with an increasing interval between the peaks and opposite evolution trends in the high-stress and low-stress zones. A larger gradient stress difference extends the "warning window" before failure, enhances macroscopic crack precursors, and increases the total crack count, with tensile cracks decreasing and shear cracks increasing linearly but at a slowing rate. Fracture patterns shift from block-like to fragmented. Higher gradient stress differences increase the proportion of total energy in the high-stress zones, with both zones experiencing more dissipated energy and less elastic energy, although dissipation remains higher in low-stress regions. This work advances the understanding of rock deformation, failure modes, and fracture characteristics in gradient stress settings, supporting future research.