Experimental study on crack characteristics and acoustic emission characteristics in rock-like material with pre-existing cracks

Grain size composition, crack pattern, and crack length have a significant influence on the crack characteristics, mechanical characteristics, and acoustic emission characteristics of rock masses. In this paper, the crack characteristics, mechanical characteristics, and acoustic emission characteristics of rock masses with different grain size compositions, different crack patterns, and different crack lengths were investigated under uniaxial compression. The rock masses were made of rock-like materials. The crack initiation locations and crack propagation directions were different for a specimen comprised of one grain size range compared with specimens comprised of two or three grain size ranges. The specimens comprised of one and three grain size ranges crack progressively. The specimen comprised of two-grain size ranges brittle fracture. The highest peak axial load was found in the specimens comprised of one grain size range. The results showed that tensile wing crack, anti-tensile wing crack, transverse shear crack, compression induced tensile crack, and surface spalling were produced in specimens with different crack orientations. The rock mass with 2 cm long crack started to produce cracks from the tip of the crack extending to the top and bottom surface, soon forming through cracks. The rock was brittle fracture. The axial load reached the maximum and then fell rapidly. The acoustic emission energy reached a rapid maximum and then decreased rapidly. The rock mass with 3 cm long fissures started to produce cracks that only extended from the tip of the fissures to the top surface but not to the bottom surface. The rock mass was progressively fractured. The axial load was progressively decreasing. The acoustic emission energy also rose and fell rapidly several times as the rock mass was progressively fractured. Different rock crack lengths led to different crack processes and crack patterns, resulting in very different acoustic emission characteristics.