Mechanical properties and fracture failure characteristics of fractured limestone under coupled freeze-thaw and cyclic loading

Abstract The Central Asian Orogenic Belt possesses abundant mineral resources. As mining activities extend into high-altitude cold regions, the safety and stability of rock engineering projects, such as open-pit mine slopes, have become increasingly prominent. This study investigates the damage deterioration process of fractured limestone under the coupled effects of freeze-thaw (F-T) cycles and cyclic loading, focusing on mechanical properties, energy evolution, and fracture failure characteristics. Furthermore, the evolution laws of macro-mesoscopic failure modes under these coupled actions are analyzed. The results indicate that the number of F-T cycles and the fracture count are negatively correlated with the fatigue life and peak strength of the rock. A significant quadratic polynomial relationship exists between various energy densities and stress levels. F-T cycles alter the energy conversion efficiency to a certain extent; specifically, the energy storage coefficient and the dissipation coefficient are negatively and positively correlated with the number of F-T cycles, respectively. Moreover, F-T cycles intensify the deterioration of the internal structure of the fractured limestone, leading to a significant increase in the proportion of shear cracks. An increase in the initial fracture count makes the rock more susceptible to coalescence failure along weak structural planes. The failure mode progressively transitions from a single tensile failure mode to a combined tensile-shear failure mode, with rock bridge regions identified as the critical weak structural planes that accelerate damage. This study elucidates the fatigue damage mechanisms of fractured limestone in alpine cold regions, providing a critical theoretical foundation for the safety assessment and disaster early-warning of high-altitude open-pit slopes.