Study on the evolution law of rock fracture damage in deep buried tunnel based on in-situ monitoring data

When constructing tunnels through dense hard rock, it is common for the adjacent rock strata to sustain fracturing. Such damage can readily precipitate severe underground construction mishaps, including occurrences of rockburst, spalling, and substantial deformations within the surrounding geological material. Employing in-field monitoring results from a subterranean research facility and numerical simulations conducted with the CASRock software, this study examines the developmental behavior and damage mechanisms inherent in the surrounding rock mass of a deep, hard-rock tunnel experiencing excavation-induced perturbations. The analysis reveals: Time-dependent rock fracturing occurs mainly in high differential stress areas with distinct directionality, driven by directional crack propagation under a true triaxial stress field; stress corrosion further promotes directional crack extension when stress reaches a critical level, enhancing this directionality. Rock mass damage is significantly correlated with its strength and integrity: high-strength intact rock masses (Grade II, RMIBT 0.75–0.90) show excavation-induced new crack propagation, while low-strength fractured ones (Grade III, RMIBT 0.50–0.75) are dominated by existing fracture expansion. During tunnel excavation, spandrel and haunch areas are core maximum principal stress concentration zones where stress accumulates with advancement; targeted advanced support or reinforcement here can effectively reduce rockburst risk and ensure construction safety. Three typical surrounding rock fracture modes (single-zone, zoned, deep-seated) are regulated by the coupling of rock mass physical-mechanical properties and excavation-induced stress redistribution. The excavation damage zone (EDZ) evolves in four distinct stages with clear quantitative thresholds, providing a scientific basis for optimizing excavation speed and determining support timing.