Quantitative detection of damage processes in granite by sound signals

Sound signals of rock cracking can be used as indicators of rock failure processes in deep rock engineering. Compression tests, including a cyclic uniaxial compression test and noncyclic compression tests (e.g., uniaxial, biaxial and rockburst tests), were conducted using a true triaxial test system to investigate the correlation be-tween sound characteristics and damage in granite cracking processes. The sound signals of granite cracking were monitored during the tests. The Kaiser effect and Felicity effect of sound were found in the cyclic uniaxial compression test. The Felicity ratio (FR) decreases continuously with increasing rock damage, which indicates that sound signals can be used to generally evaluate rock damage. In addition, the zero-crossing rate (ZCR), a characteristic index of sound signals, was proven to be applicable to quantitatively detect damage processes and construct damage constitutive models in granite. Furthermore, a novel sound-based index, namely the total energy of local sound (TELS), was proposed to evaluate the cracking intensity for granite. Experimental results show that sound signals are useful indicators for the quantitative detection of damage processes in hard rock under high stress conditions.