Experimental Study on Acoustic Emission Characteristics in the Fracture Process of Granite Under Dry and Saturated State

摘要

Abstract To investigate the evolution characteristics of internal cracks during deformation and failure of dry and saturated granite samples, uniaxial and triaxial compression acoustic emission tests were carried out. The variation law of acoustic emission time-domain information and peak frequency distribution characteristics of dry and saturated granite samples in different crack propagation stages were analyzed. The fracture evolution characteristics of dry and saturated granite samples and the influence of water on the crack propagation process were studied. Based on the acoustic emission signal characteristic parameters RA (rising time/amplitude) and AF (ringing count/waveform duration), the distribution of micro tension/shear cracks and its relationship with macroscopic failure of samples were revealed. The results show that the acoustic emission ringing count and energy of dry samples are larger than those of saturated samples, and the b-value shows the characteristics of decreasing–increasing–decreasing during loading. The frequency band number of acoustic emission signals of saturated samples is significantly higher than that of dry samples, and the percentage of signal distribution in low-frequency and intermediate-frequency bands is higher than that of dry samples, while the percentage of signal distribution in high-frequency bands is lower than that of dry samples. The large-scale cracks of saturated samples are more than that of dry samples, while the small-scale cracks of dry samples are more. The shear cracks of dry samples are more than those of saturated samples. With the increase of confining pressure, the shear cracks of samples gradually increase. The change law of the micro-crack type reflected by RA-AF distribution characteristics is consistent with that of the macro-failure mode.