Abstract:
To explore the relationship between stress path and emission characteristics during failure process, the conventional triaxial compression test, and constant axial stress and unloading confining pressure test were performed on marbles. The results show that acoustic emission features differ with stress paths. In the conventional triaxial compression experiment, the maximum of acoustic emission count rate takes place at the sudden drop point of stress, behind the stress peak, while the acoustic count rate maximizes at the stress peak during the experiments of unloading confining pressure. Before the conventional triaxial compression failure, the acoustic emission of the rock sample is alternated between the fluctuating and quiet period, and the paths of constant axial stress and unloading compression are characterized by burstiness. Under a low confining pressure, the experiment of unloading confining pressure reveals that the acoustic emission count rate falls evidently at the unloading position, and a higher confining pressure will result in a rock failure lasting longer and a higher acoustic count rate at the time of failure. In addition, a higher rate of unloading pressure will bring a shorter quiet period to the sample unloaded, and hence a higher maximum acoustic count rate during the whole failure process. When unloading occurs at the plastic stage, there will be a small amount of acoustic emission occurring with a relatively high count rate, but comparatively lower than the rate in the rock failure process.