Abstract: In order to study the failure strength and crack propagation characteristics of fractured rocks, the uniaxial compression experiments on rocks with single fissure were carried out by MTS rock mechanics system. Acoustic emission(AE), ultrasonic testing and camera recording were monitored simultaneously to study the relationships between stress-strain behaviors, acoustic emission characteristics, the propagation and coalescence of cracks. The results show that the variations of crack initiation stress, peak strength(PS) and modulus are consistent with the inclination angle ? of fissure, which decreases firstly then increases later. Crack initiation stress and peak strength are affected greatly by ?. The stress-strain curves of fractured rocks rise stepwise before peak strength attributed to the stress transference and stress release (stress drop) induced by intermittent accelerated propagation of cracks. The stress drop is accompanied with energy release, modulus deterioration and sharp increase in ring counts of acoustic emission. With the increase in ?, the stress corresponding to the first stress drop and sharp increase in ring counts of acoustic emission gradually increases. Besides, the ring distribution gradually shifts to peak strength. The initiation and propagation of cracks result in the attenuation of wave amplitude and velocity, and the amplitude decrease occurs earlier than that of stress drop. The velocity decrease of rock sample with ??= 0o reaches up to 50% before peak strength. With the increase in ?, the stress increases at the moment corresponding to the velocity drop, and the drop rate of wave velocity before peak strength decreases gradually. When ? is small, crack propagation is highly developed before peak strength of rock. It shows that with the increase in ?, crack development before peak strength subsides. Thus the accelerated crack propagation and convergence transfer to post-peak stage. When the crack length is extended to a critical value, the expansion rate will increase rapidly. The threshold of crack length gradually decreases as ? increases.

Key words: rock-like material, ultrasonic velocity, acoustic emission, crack propagation