Unveiling the regulatory mechanisms of rock fracture behavior and catastrophic failure predictability: The key role of porosity

This study investigates the influence of porosity on the Mode I fracture behavior of granite and the predictability of catastrophic failure. Pores are defined in a broad sense to include intrinsic pores and microcrack-type defect structures that collectively contribute to rock heterogeneity. Granite specimens were heat-treated at ambient temperature, 450 °C, and 900 °C to induce porosity variations, which were quantified using Nuclear Magnetic Resonance (NMR). Three-point bending (TPB) tests were conducted with real-time monitoring using Digital Image Correlation (DIC) and Acoustic Emission (AE). The results show that increasing porosity significantly reduces rock strength, fracture toughness, and fracture energy. As porosity increases from 0.68% to 1.33%, the crack initiation and unstable fracture toughness decrease by 94.6% and 87.0%, while crack mouth opening displacement (CMOD), fracture process zone (FPZ) size, and fracture surface roughness increase. AE results indicate that low-porosity specimens exhibit few high-energy events typical of abrupt brittle fracture, whereas high-porosity specimens generate numerous low-energy events associated with distributed microcrack coalescence. Time-Reversed Omori Law (TROL) analysis shows that higher porosity leads to predicted failure times closer to actual collapse, indicating improved predictability. These results demonstrate that pore-related heterogeneity plays a key role in regulating fracture behavior and catastrophic failure predictability.