Damage evolution characteristics and deterioration mechanism of mechanical properties of sandstone subjected to drying-wetting cycles

Abstract

The dams formed by rock pillars around underground reservoirs are frequently subjected to drying-wetting cycles, so that rock pillars may be deformed, broken and develop a large number of fractures. This further causes a massive loss of water and heavily affects the stability of the dam formed by rock pillars. To explore the damage evolution characteristics and the deterioration mechanism of mechanical properties of sandstone under drying-wetting cycles, mechanical tests were carried out on sandstone samples subjected to different numbers of drying-wetting cycles. Acoustic emission technology was used to real-timely monitor the failure process of sandstone under loading. At the same time, damaged rock samples were observed under a scanning electron microscope. On this basis, the development characteristics of fractures in the sandstone were analyzed, damage evolution of sandstone in different stress loading stages was expounded. Research results show that the more the drying-wetting cycles are, the more obvious the compaction stage and the more significant the deterioration of the peak strength and elastic modulus, accompanied by the gradual decrease of the strain energy and cumulative acoustic emission count. According to scanning electron microscope observations, fractures inside the sandstone increase in quantity and begin to coalesce after 10 drying-wetting cycles, so that loose particles and fracture degree gradually rise, and accumulation of damage causes mechanical properties of sandstone to gradually deteriorate. The research results provide a solid theoretical basis for stability evaluation and protection of dams formed by rock pillars around underground reservoirs in goaf.