Study on acoustic emission characteristics of sandstone under different fracture modes

To investigate the characteristics of the sandstones under two fracture modes which are tensile fracture and shear fracture, we proposed three-point bending test and a modified shear test. Meanwhile, numerical simulations using particle flow code (PFC) and acoustic emission (AE) analysis are performed to obtain their differences. The AE hits and amplitude analyses prove that no matter which mode, they experience obvious three stages. The AE hit curve and amplitude are lower in the first stage. Then, the curve goes up steadily and the amplitude value becomes relatively large in the second stage. Entering into the third stage, the curve increases quickly to its peak value and a lot of AE signals with higher amplitude are generated. Moreover, AE b-value analysis is also used to make crack magnitude assessment. It was obvious that the distribution of b-value curve can be divided into three stages, which are just corresponding to the division of AE hits and amplitude distributions. The b-values are diverse and fluctuating largely in stage I and then show small fluctuations and have increasing trends in the whole process in stage II whereas finally exhibit sharp down to the minimum points at the stage III. The average b-values for tensile fracture tests are in the range of 0.877–1.09 whereas for shear fracture tests are within the range of 0.815–0.876. Comparing to tensile fracture, when shear fracture occurs in the rock sample, the AE energy releases faster and the proportion of large magnitude cracks is larger. The research results in this article could make more instructive and applied value to in situ non-destructive monitoring of fissure development for engineering rock mass.