Experimental research on ultrasonic velocity and acoustic emission properties of granite under failure process

The experiments on granite under uniaxial compression and cyclic stress loading are carried out, and changes in velocity and the activities of acoustic emission are recorded by the ultrasonic velocity and acoustic emission synchronous monitoring devices. The results show that: (1) In the beginning of the loading tests, the shear-wave velocity and longitudinal-wave velocity have a significant ascension due to the closure of rock micro-cracks, while the AE events are rare; the granite is in the linear elastic deformation stage in the middle of compression experiments, the ultrasonic velocity increases firstly and then keeps stable for a while, and a small amount of AE events, about 8.77% of all the AE events, will occur; because of generating and expanding of cracks in the rock samples, the granite will suffer serious damage in the later period of compression tests, the longitudinal-wave velocity decreases slightly and the shear-wave one reduces significantly, and AE has positive activities, about 50.96% of all the AE number. After the stress peak, the shear-wave velocity begins to reduce sharply and the longitudinal-wave one decreases slowly, while the AE remains active. (2) Because the rock damage needs enough energy accumulated, the AE exhibits a law of “quiet relatively and bursting at intervals”, and the most evident “ relatively quiet period” happens before the peak stress. (3) In the tests of cyclic stress loading, the ultrasonic velocity and AE activities of the rock have a good consistency with stress condition. Change of AE events at peak stress can reflect accumulated damage of the rock, and the Felicity effect can be demonstrated by comparing the AE events at the same stress stage.