Degradation of Fracture Characteristics on Coconino Sandstone Due to Water Content

Abstract

The water content of a rock affects its fracture characteristics, such as strength and fracture toughness. In this study, the effect of water content on the fracture characteristics, such as strength, fracture toughness and subcritical crack growth index under shear loading for Coconino sandstone was investigated. Here, experiments were conducted in two cases: completely dry and fully saturated. In particular, a short-beam compression specimen was employed to examine the fracture characteristics due to shear; in addition, the shear strength, mode II fracture toughness, and subcritical crack growth index under shear stress were obtained. Consequently, the shear strength and mode II fracture toughness decreased as the water content increased; however, the subcritical crack growth index remained almost the same without significant alterations. The effect of water on the strength reduction of rocks is related to chemical and physical corrosion, pore pressure increase, and frictional reduction. Previous investigations on the deterioration of strength by water have yielded similar results in this research. Under saturated conditions, the shear strength decreased by 15.5%, and the fracture toughness decreased by 11.8%, compared with dry conditions. Regardless of the dry or saturated condition, the subcritical crack growth index n exhibited similar values.