Experimental Study on the Effects of Salt Water on the Dynamic Mechanical Properties of Sandstone

Through the preparation of five NaCl solutions with varying concentrations to simulate a deep saline aquifer environment, sandstone specimens were immersed in these solutions for 28 days. Basic physical parameters, mineral composition, and micromorphology were then tested to investigate the physicochemical damage behavior of sandstone under deep saline conditions. Subsequently, impact compression tests were conducted using a split Hopkinson pressure bar (SHPB) apparatus to explore the coupling relationship between saline immersion and the damage mechanisms as well as the dynamic mechanical behavior of sandstone. The results indicate that as the NaCl concentration increases, the mass increase rate of the specimens rises gradually, while the volume expansion rate and density growth rate exhibit fluctuating trends, with fluctuation amplitudes remaining below 0.041% and 0.089%, respectively. It is observed that ion exchange between Na⁺ and Ca²⁺ on the specimen surface is primarily induced by the NaCl solution, accompanied by partial mineral dissolution. When the mass fraction of NaCl is less than 10%, the dynamic compressive strength, dynamic peak strain, strain rate, and average fragment size are all found to decrease gradually; when the mass fraction exceeds 10%, the dynamic compressive strength, dynamic strain, and strain rate are shown to increase according to a power function relationship, while the average fragment size follows an exponential growth pattern. Compared with specimens in their natural state, the dynamic compressive strength, dynamic strain, strain rate, and average fragment size of sandstone treated with NaCl are all reduced, and the degree of damage is observed to be more severe. This study reveals the evolution patterns of mechanical properties and the damage mechanisms of sandstone specimens in saline environments, and provides a theoretical basis for the long-term stability evaluation of surrounding rock in deep saline aquifer-related engineering.