Shear failure modes and AE characteristics of sandstone and marble fractures

To study the shear failure modes of rock fractures with different morphologies, rock types and test conditions, direct shear tests were conducted with the aid of an acoustic emission test system to obtain the characteristics of acoustic emissions in the shear process. The test results indicated that sandstone fractures experienced brittle shear failure under higher constant normal loads (15-30 kN) and plastic shear failure under lower normal loads (5 kN and 10 kN), while the marble fracture experienced plastic shear failure under each normal load. Dropping of shear stress, sharp change from shear dilatation to shear shrinkage and sudden release of high AE energy could be found when brittle shear failure occurred in sandstone fracture under a higher normal load. Thus, combining the location evolution characteristics of acoustic emission, it can be concluded that the entire shear dislocation of sandstone fracture in brittle shear failure mode happened just after the peak under higher normal loads. However, the entire shear dislocation of sandstone fracture under lower normal loads and marble fracture under all normal loads occurred just at the beginning of the shear process