Experimental study on coupled effects of water and sub-zero temperatures on mechanical behavior and damage evolution of sandstone under uniaxial compression

Severe cold conditions and significant seasonal temperature fluctuations in cold regions profoundly influence the mechanical properties of rocks, posing critical challenges to the safety and operational efficiency of open-pit mining. To explore the coupled effects of water and subzero temperatures on the mechanical behavior and damage evolution of sandstone, several uniaxial compression tests were conducted on water-saturated specimens under temperature conditions ranging from 20 °C to −40 °C. By integrating digital image correlation (DIC) and acoustic emission (AE) techniques, the surface strain localization and internal crack evolution were captured simultaneously. The results reveal that subzero temperatures enhance both the strength and energy absorption capacity of sandstone. As temperature decreases, the uniaxial compressive strength, failure displacement, and energy parameters (including elastic, dissipated, and post-peak energies) increase progressively, with elastic energy exhibiting the most notable improvement. Subzero temperatures also significantly affect the damage evolution process, delaying damage progression while amplifying damage accumulation during plastic stage. In addition, failure modes transition sequentially with decreasing temperature, from tensile-shear mixed failure at 20 °C, to shear-dominated failure between 0 °C and −20 °C, and back to tensile-shear failure below −30 °C. Furthermore, the freezing of pore water alters the loading process, with ice crystal formation enhancing rock strength. Below − 30 °C, extensive pore water freezing inhibits crack propagation, leading to an abrupt failure process. These findings advance the understanding of the mechanical behavior of rocks in cold environments and provide guidance for optimizing mining engineering in cold regions.