Experimental study on the strength and fracture mechanism of sandstone containing elliptical holes and fissures under uniaxial compression

To investigate the strength and fracture mechanism of flawed rock, a series of uniaxial compression tests on sandstone specimens containing elliptical holes and fissures were carried out using acoustic emission (AE) monitoring and digital image correlation (DIC) system. Based on the experimental results, the stress-strain curve, mechanical parameters, AE counts and strain field evolution were analysed, and they indicated that the ligament angle is a significant factor influencing the strength and deformation of pre-flawed sandstone specimens. As the ligament angle increases, the peak strength, peak strain and elastic modulus first decrease and subsequently increase. Observations show that a stress fluctuation corresponds to an inflexion point in the accumulated AE count curve and AE counts reach the maximum value at or after peak strength. Additionally, the highlighted strain localization zones are indications of crack initiation, and crack propagation behaviour is a progressive evolution of the highlighted strain localization zones. Based on an analysis of the ultimate failure patterns, four types of rock bridge coalescence modes are identified, i.e., no coalescence, shear coalescence, double-shear coalescence and double-tensile coalescence.