Experimental Investigation on Crack Behavior and Stress Thresholds of Sandstone Containing a Square Inclusion under Uniaxial Compression

Featured Application The present work is conducive to understand the effect of filling on the deformation and failure of rock and to accurately determine the crack stress thresholds of rock with holes or inclusions. To study the effect of strength, stiffness and inclination angle of square inclusions on failure characteristics of rock, uniaxial compression tests were carried out on prismatic sandstone containing a square hole with different filling modes and hole angles using a servo-hydraulic loading system. Digital image correlation and acoustic emission techniques were jointly applied to analyze the damage and fracture process, and the crack stress thresholds were determined qualitatively and quantitatively by combining the stress-strain behavior. The results show that the mechanical properties and crack stress thresholds of pre-holed specimens increase with the increase of the strength and stiffness of inclusions, and are affected by the hole angle. Rock failure is mainly caused by secondary crack propagation and shear crack coalescence, eventually forming mixed tensile-shear failure. The crack behavior, especially the crack initiation position, is affected by the filling mode and the hole angle. Interface debonding tends to initiate at the vertical interface, while interface slipping tends to propagate along the inclined interface. Under identical loading conditions, the specimen with 45 degrees hole is more susceptible to crack and damage than that with 0 degrees hole. Notably, inclusions can inhibit the hole deformation and the fracture of rock matrix, especially the sidewall spalling of 0 degrees hole.