Research on Damage Characteristics and Mechanisms of High-Temperature Water-Immersed Rocks Based on CT Scans

To address the deterioration and instability of surrounding rock in deep coal mines under the long-term coupling effect of high-temperature water and mining stress, sandstone with three temperature gradients and a water immersion time of 3–45 days was selected as the test object. Uniaxial compression-acoustic emission (AE) tests were carried out, and the fracture morphology was reconstructed by computed tomography (CT) technology. The results showed that: (1) Mechanical properties are significantly affected by water immersion time and temperature. The deterioration rate of peak strength ( and elastic modulus ( E ) decreases exponentially with the water immersion time, while high-temperature water immersion accelerates the damage and deterioration process. (2) The AE behavior of sandstone after water immersion changes from the dry and brittle post-peak burst to pre-peak continuous activation. The energy shifts from energy storage dominance to energy dissipation dominance. The energy dissipation conversion rate of 85–30 days increased by 8.92% compared with 25-30 days. (3) CT and fractal statistics show that the fracture geometry and rupture mode have shifted from "axial tension" to "tension-shear mixed dominance" and tend towards shearing. High-temperature water immersion significantly promotes network connectivity and roughening, and fractal dimension ( V D ), volume fraction ( V r ) and permeability ( K ) increase simultaneously, ultimately leading to a "thick banded" through-shear body, with K increasing by a maximum of 82.14%. (4) NMR and SEM show that increased water temperature accelerates the hydrolysis and dissolution of sandstone minerals, significantly expands pore throats and enhances connectivity, gradually weakens the cementation between framework particles and causes relative slippage, ultimately forming shear-dominated failure, increased permeability and enhanced anisotropy. This study provides experimental basis and index system for the stability assessment and water inrush prevention of surrounding rocks in deep tunnels and high-temperature mines. • High-temperature water immersion accelerates the rock damage process, with active pre-peak aberration (AE) signals. • The differences in V D , V r , and K in fractured bodies were quantified through CT scan reconstruction. • The mechanism of synergistic degradation of sandstone macro- and microstructures under high-temperature water immersion was revealed.