Study on damage mechanical properties and energy evolution mechanism of rock under different freeze-thaw conditions

This study aims to investigate the damage mechanical properties of sandstone and its energy evolution behaviour under various freeze-thaw conditions, clarifying the synergistic effects of freeze-thaw cycle duration and the number of cycles on the rock mechanical deterioration and energy damage mechanism. Sandstone from the roof of No.8 coal seam at Tashidian Coal Mine in Xinjiang was selected as the research subject. Freeze-thaw experiments were conducted with different freeze-thaw cycle durations (6 h, 12 h, 18 h, 24 h) and different freeze-thaw cycles (5 times, 10 times, 15 times, 20 times). Uniaxial compression tests were performed to obtain peak stress, peak strain, and elastic modulus variations. Based on energy calculation principles and the principle of minimum energy dissipation, the evolution mechanism of energy damage under different freeze-thaw conditions was revealed. The results indicate that freeze-thaw damage increases with longer cycle durations and more freeze-thaw cycles. Peak stress and elastic modulus of the rock are negatively correlated with freeze-thaw periods cycle duration and number, while strain shows a positive correlation. According to energy principles, during the OA-compaction stage, energy storage and dissipation exhibit minor changes. In the AB-linear elastic deformation stage, stored elastic strain energy gradually decreases with increasing freeze-thaw duration and cycles. During the BC-plastic deformation stage, the proportion of elastic strain energy to total strain energy gradually decreases, whereas the dissipated energy proportion increases, indicating accelerated internal damage with increased freeze-thaw duration and cycles. In the CD-post-peak failure stage, stored elastic strain energy rapidly converts to dissipated energy accompanied by energy release. Furthermore, prior to peak stress, the rate of elastic strain energy accumulation is weakened due to freeze-thaw effects, reaching its minimum at peak stress. The study demonstrates that freeze-thaw cycle duration has a greater impact on mechanical degradation than the number of cycles, and their synergistic effect exacerbates rock damage. These findings provide a theoretical basis for cold region engineering construction, rock damage assessment, and freeze-thaw damage prevention and control.