Experimental Study on Mechanical Properties, Acoustic Emission Energies and Failure Modes of Pre-cracked Rock Materials under Uniaxial Compression

To better understand the basic properties and phenomena of compression failure in rock mass structures, a series of uniaxial compression tests on sandstone specimens was carried out using loading equipment, an acoustic emission system, a computed tomography scanning system and a high-speed video camera. The results showed that the fracture process of sandstone samples was divided into three stages: original micro-crack closure, micro-crack nucleation and macro-crack propagation. Avalanche energies of the intact and single-fissured specimens followed a power-law distribution, which revealed avalanche criticality. The optimal exponents ($r$) of single-fissured specimens were about 1.64 and were slightly lower than that of the intact specimen. The fitted power-law exponents ($r^{\prime }$) of sandstone specimens change in the different stages of experiments and gradually tend to a stable value, which acted as a "warning signal" for the impending major collapse. Based on histogram analysis and the maximum likelihood method, the presence of a flaw may affect the statistical properties of avalanche energies. The flaw inclination angle had little influence on the optimal exponent, but it had certain influence on the fracture modes of the specimens. This paper may provide a new theoretical basis for predicting the collapse failure of engineering rock mass structures.