Study on Conventional Triaxial Mechanical Properties and Energy Evolution Patterns of Red Sandstone Under Brine Erosion

With the increasing depletion of shallow resources, marine-based mineral resources in coastal and continental shelf areas are poised to become a new frontier for resource development. However, ions in brine solutions undergo complex water-rock interactions with rocks, affecting the engineering stability of marine-based rock masses. This study addresses engineering safety concerns arising from the long-term coupled effects of brine erosion and confining pressure on rocks during seabed mineral resource extraction. Using red sandstone as the research subject, it investigates the evolution of its mechanical properties under complex brine-erosion conditions. Experiments involved immersing red sandstone specimens in simulated seabed brine solutions for erosion cycles of 14, 21, and 35 days. Triaxial compression tests were conducted under confining pressures of 5 MPa, 10 MPa, and 15 MPa to systematically analyze the effects of erosion duration and confining pressure on rock strength, deformation, energy characteristics, and failure modes. Results indicate that brine erosion significantly reduces the strength and elastic modulus of red sandstone, but the effect is not simply linear. Instead, it follows a trend of initial slight strengthening followed by significant deterioration. During short-term erosion (21 days), some mechanical parameters slightly recovered, potentially due to temporary filling of fractures by brine ions. After long-term erosion (35 days), all mechanical properties markedly declined. This study aims to reveal the triaxial mechanical properties and energy evolution patterns of red sandstone under multi-ionic brine erosion, providing crucial experimental evidence for designing safe isolation layers and evaluating long-term stability in seabed mining.