Abstract: For the construction safety of underground engineering and prediction & warning of disasters, the fracture mechanical behavior and acoustic emission (AE) characteristics of fractured rock masses under hydro-mechanical coupling condition are key concerning problems. This study carries out compression failure experiments with the cement mortar material and AE technique, and investigates the failure modes, mechanical properties and AE characteristics of specimens containing 3-D crack under dry and hydro-mechanical coupling condition. The influences of crack dip angle and water pressure on the specimen failure and mechanical behavior, as well as the relation of dominant frequency characteristics of AE signals with the specimen failure status are analyzed. The experimental results indicate that the failure mode of specimen changes from tensile-dominant mode to tensile-shear mixed mode and finally shear-dominant mode as the crack dip angle increases. High water pressure enhances the tensile failure mode of specimens, while the shear failure mode is weakened to some extent. With the increase of water pressure, the crack initiation stress, damage stress and the peak strength of specimens decrease continuously, and the influence of water pressure on the initial stress and peak strength exhibits a threshold effect (4 MPa). The AE hit rate during the failure process of specimens presents an evident stage characteristic, which provides a reference base for the adjudgment of crack initiation and damage stress. Additionally, the AE signals exhibit different dominant frequency characteristics at different failure statuses of specimens, and the dominant frequency ranges of relatively high, intermediate and low frequency signals are discontinuous. The proportions of relatively-low-frequency and relatively-high-frequency signals correspond to different failure statuses of specimens, which can provide references for the rock mass failure prediction and warning.

Key words: hydro-mechanical coupling, 3-D crack, acoustic emission, failure mode, mechanical property, dominant frequency characteristics