Experimental study on acoustic emission failure precursors of marble under different stress paths

There are diverse acoustic emissions during the process of rock deformation and breakage in various stress paths. To explore the relationship between emission failure precursors and stress paths, loading and unloading tests on marble under different stress paths are carried out. The results show that: (1) According to the growth rate of accumulated ring count rate before failure and the emission count rate at failure point, the sequence of stress paths from the largest to the smallest is loading axial stress and unloading confining pressure, constant axial stress and unloading confining pressure, uniaxial compression, and conventional triaxial compression. (2) Before failure under conventional triaxial compression, there exists an obvious low emission period of acoustic emission count rate. The larger the confining pressure, the more obvious the low emission period as the failure precursor. Rock samples fail within a very short time after the inflection point of growth rate of accumulated count rate appears. (3) The growth rate of accumulated count rate of constant axial stress and unloading confining pressure tests at failure point is approximately tangent with the low confining pressure. There is a quiet period of acoustic emission count rate after close count rate before failure of loading axial stress and unloading confining pressure samples. The duration of the quiet period increases with the confining pressure, and rock failure leads to a higher count rate. (4) When the stress ratio is more than 0.8 under low confining pressure or the time ratio is more than 0.4 under high confining pressure, the decreasing characteristics of fractal dimension of acoustic emission can be regarded as the failure precursor of rock.