Abstract: Although many achievements have been made on the application of Acoustic Emission (AE) technique to monitoring crack propagation in rock mass, these studies mainly focused on rock block of small size (≤10 cm). Only a few investigations have been done to research the failure mechanism of larger rock mass (≥50 cm). The SAMOS acoustic emission instrument was employed to study the failure process of jointed rock mass in field shear test. Based on analysis of AE parameters and frequency spectrum acquired from the shear failure process of jointed rockmass, its failure mechanism can be revealed. The results showed that during the failure process of jointed rock mass, the main frequency of AE signals varied from 40 kHz to 120 kHz. The shear failure went through four phases: first, elastic deformation phase, during which no AE events happened in rock mass; second, crack initiation phase, in which a few AE events occurred and only a few cracks were generated; third, crack propagation phase when AE events increased slowly and cracks propagated steadily; and fourth, crack coalescence phase when AE events increased apparently, cracks propagated and coalesced and macro fractures appeared. Different from the traditional viewpoint, which deems that the crack appears at the forward section of rock specimen, this research finds that the initial cracks appears at the middle and back-end of the specimen. With the increase of shear stress, the locations of new cracks move to the forepart. However, during the crack coalescence phase, the cracks fastened on local positions of the shear surface. Local cracking happened in jointed rock mass.

Key words:  jointed rock mass, shear failure, acoustic emission, time sequence characteristic, failure mechanism