Impact of water saturation on the deterioration of mechanical properties and damage mechanisms of sandstone composites

In-depth research on the impact of water saturation on the mechanical properties of rocks is crucial for safe and reliable rock engineering. This study conducted uniaxial compression tests and acoustic emission (AE) monitoring on coarse-grained sandstone, fine-grained sandstone, and their composites under natural and saturated water conditions. The results revealed that under saturated water conditions, the mechanical properties of coarse-grained sandstone deteriorated significantly, with peak stress (σp), crack damage stress (σcd), crack closure stress (σcc), and elastic modulus (E0) decreasing by 35%, 52%, 33%, and 47%, respectively. The deterioration of fine-grained sandstone was less severe, with σp, σcd, σcc, and E0 reducing by 13%–24%. The mechanical properties of the composites were significantly affected by the water state. Under natural water conditions, the σp, E0, and σcd values of the composites were between those of the individual rock samples. However, when the composites contain saturated samples, the σp, σcd, and σcc of the composites were lower than those of the individual rock samples. Under saturated conditions, the total absorbed energy (U) and stored elastic energy (Ue) of the rock samples decreased, AE counts and crack signals reduced.