Study on the mechanical degradation and acoustic emission characteristics of weathered sandstone

Weathered sandstone is highly susceptible to water-induced softening and instability because of its weak cementation, loose fabric, and well-developed pore connectivity. This study investigates the mechanical degradation and fracture evolution of weathered sandstone from Sichuan, China, under dry and saturated conditions. Thin-section observation and nuclear magnetic resonance tests were first conducted to characterize mineral composition and pore structure. Uniaxial compression tests coupled with acoustic emission (AE) monitoring were then performed, and the fracture process was analyzed using a Gaussian mixture model, scanning electron microscopy, avalanche dynamics, and critical slowing down (CSD) theory. The results show that the sandstone has a clastic texture, weak clay cementation, and an average porosity of 14.53%, providing favorable pathways for water infiltration. Saturation significantly weakens the rock, reducing uniaxial compressive strength, elastic modulus, and failure strain by 68.3%, 61.2%, and 30.8%, respectively. AE responses indicate that dry specimens fail through concentrated high-energy release and abrupt brittle rupture, whereas saturated specimens exhibit dispersed energy release and progressive shear-dominated failure. The power-law exponent of AE energy increases from 1.99 to 2.23 after saturation, suggesting that water suppresses high-energy events and multiscale crack cascades. CSD-based early-warning analysis shows that amplitude variance is the most effective precursor for dry specimens, while energy variance provides the best warning performance for saturated specimens. These findings clarify the water-induced degradation mechanism of weathered sandstone and provide guidance for the stability assessment and early warning of weathered rock masses.