Failure Behavior of Sandstone Specimens Containing a Single Flaw Under True Triaxial Compression

An experimental study of the failure behavior of sandstone specimens containing a single flaw under true triaxial compression was conducted. The main objective was to investigate the influences of the intermediate principal stress on the cracking pattern, stress-strain response, and acoustic emission (AE) activities. The results revealed that a higher intermediate principal stress resulted in higher specimen strength for constant minimum principal stress. The peak load of the test specimens generally increased with an increase in the flaw inclination angle. The crack initiation stress under true triaxial compression initially increased and then decreased with an increase in the intermediate principal stress at a constant minimum principal stress. The flawed specimens typically failed due to anti-wing cracks, regardless of the flaw inclination angle and the intermediate principal stress. The crack initiation angle was primarily determined by the flaw inclination angle. The rise time/maximum amplitude (RA) and the average frequency (AF) were used to identify the cracking type. The proportion of shear cracks was much higher than that of the tensile cracks during the cracking process. The proportion of shear cracks increased with the external load, whereas that of the tensile cracks decreased. The number of crack events decreased and then increased with an increase in the intermediate principal stress. A damage model that considered microscopic damage resulting from microcracks and macroscopic damage resulting from the pre-existing flaw was proposed to describe the failure behavior of rock specimens containing a single flaw under true triaxial compression.