Fracture analysis of sandstone with a single filled flaw under uniaxial compression

Natural rock joints with infilling materials such as clay, broken rock fragments, or even cement mortar infusion material are common in the field of rock engineering. The fracture behavior of a rock with a filled flaw is related to both the flaw inclination and mechanical properties of the infilling materials. In this study, uniaxial compression experiments were performed for sandstone specimens with different flaw inclinations varying from 0 degrees to 90 degrees, and four kinds of infilling conditions, including no filler, gypsum filler, cement filler, and resin filler were considered. The damage process of specimens was revealed and traced by acoustic emission (AE) and digital image correlation (DIC) to comprehensively understand the cracking evolution. Macroscopic cracking information was recorded with a high-resolution camera, and crack patterns were identified and classified. The influence of infilling material and flaw inclination on the sandstone cracking process was studied. The tensile stress was found to be suppressed due to the existence of infilling materials, and different infilling materials have different effects on the crack initiation stress. As a result, specimens with a filled flaw have larger crack initiation stress levels and smaller crack inclination angles than specimens with an unfilled flaw. The effects of infilling materials and flaw inclination angles on crack initiation are analyzed with a theoretical model based on the Coulomb friction law. The compressibility effect of infilling materials on the cracking behavior is also investigated through displacement and strain fields.