Experimental study on the shear and acoustic emission characteristics of jointed rocks

Abstract The strength mechanism of jointed rocks remains poorly understood. In this paper, direct shear tests were performed on three rock types (intact, continuous jointed, discontinuous jointed rocks) using similar brittle materials and monitored using an acoustic emission device. The undulation a...
Ausführliche Beschreibung

Abstract The strength mechanism of jointed rocks remains poorly understood. In this paper, direct shear tests were performed on three rock types (intact, continuous jointed, discontinuous jointed rocks) using similar brittle materials and monitored using an acoustic emission device. The undulation angles of the continuous joints and dip angles of the discontinuous joints were 0°, 30°, 45°, and 60°. The results show that the failure mode of the continuous jointed rocks is controlled by the undulation angle and normal stress conditions. Under low normal stress (< 0.3 MPa), the continuous jointed rocks underwent four stages: nonlinear compression densification; linear elastic deformation; sawtooth fracture; and residual section slip. The strength of the continuous jointed rocks reached a maximum at an undulation angle of 45° under low normal stress. The dip angle and rock bridge fracture mode differ during the shearing process of discontinuous jointed rock, which underwent four stages including non-linear compression (crack closure), linear deformation (fine crack extension), non-linear deformation (crack extension penetration), and slip of the penetration surface. The shear strength of the discontinuous jointed rock initially decreased with increasing dip angle to a minimum at 45° and then increased. The acoustic emission ring count, energy, and amplitude results are in good agreement with the rock-shearing process. The investigated acoustic emission parameters reached maxima prior to the peak strength, and crack development within the rock was most intense prior to the continuous-slip damage. The acoustic emission reaches a minimum peak amplitude for a joint dip angle of 45°, which is consistent with the lowest rock strength at this angle in both intact and discontinuous jointed rock. Ausführliche Beschreibung