Integrated Physical Microstructure and Mechanical Performance Analysis of the Failure Mechanism of Weakly Cemented Sandstone Under Long-Term Water Immersion

The duration of water immersion significantly affects the mechanical response of rock materials. This study investigated the weakly cemented sandstone from the Wulagen Open-pit Mine to examine how varying immersion times affected the mineral composition, micro-porous structure, and macro-mechanical properties of the sandstone. The current study aimed to explore the mechanisms underlying the degradation of the strength and deformability of sandstone due to prolonged water exposure. The analysis showed that immersion time notably influenced the pore structure as well as the mineralogical characteristics of weakly cemented sandstone. These changes were the primary factors leading to alterations in its mechanical properties and failure modes. Specifically, with increasing immersion time, clay minerals absorbed water and expanded, with the most significant expansion occurring between 30 and 60 days. This rapid internal crack growth led to an exponential decrease in compressive strength and elastic modulus, with the most significant decline occurring between 30 and 60 days. The failure mode of the sandstone transitioned from extensional fracture to shear failure. Acoustic emission analysis revealed that, in the dry state, tensile cracks were about three times more prevalent than shear cracks, while after 60 days of immersion, shear cracks accounted for over 80%. After 60 days of immersion, microscopic cracks were fully interconnected, and the mechanical properties of the sandstone showed minimal change, with shear failure becoming predominant. These experimental results provide theoretical guidance for preventing the collapse of slopes composed of weakly cemented rock under long-term immersion conditions.