Experimental study on mesostructural damage evolution of sandstone subjected to freeze-thaw cycling under uniaxial compression

In perennially frozen or seasonally frozen soil regions, freeze-thaw cycling adversely impacts the mechanical properties of rock mass, resulting in landslides, rock erosion, and other geological disasters. The microscopic damage evolution law of loaded sandstone under the freeze-thaw cycle is analyzed by conducting Nuclear Magnetic Resonance (NMR) and uniaxial compression acoustic emission (AE) experiments. The experimental results have shown that: (1) Freeze-thaw cycling increases sandstone's internal pores, enlarges the pore size, and modifies the original pore distribution. (2) The damage due to freeze-thaw cycling is positively correlated with the initial damage to the rock, and the damage on the rock surface is more severe than inside the rock sample. (3) Freeze-thaw cycling negatively impacts the mechanical properties of sandstone, and the elastic deformation stage of sandstone gradually decreases as the number of freeze-thaw cycles increases and gradually transitions from brittle failure to ductile failure. (4) The characteristic parameters of AE ringing count and accumulated energy can reveal the severity of freeze-thaw damage and the dynamic evolution process, and the damage development rate exhibits abrupt changes at critical moments. After five freeze-thaw cycles, the damage development rate rises suddenly, as manifested by a sharp increase in the frequency and energy of AE events. High-energy AE events frequently occur during the rapid expansion period of damage, which can be adopted as an essential reference for damage propagation and aggravation.