Acoustic Emission (AE) can provide wealthy information on the failure process of rock mass, which makes it possible to visualize the process of rock damage. In order to study the AE signature of sandstone, three kinds of specimens with different bedding orientations were selected for uniaxial compressive tests accompanied by an AE monitoring system. The failure modes of these specimens were clearly affected by structural plane, and can be divided into three categories: tensile-split along the weaker bedding plane (TD), tensile fracture across the weaker bedding plane (TM) and sliding failure along the weaker bedding plane (SD). Not only the simple counting of the number of AE events vs. different stress levels and accumulated AE energy with an inelastic strain rate were studied, but the frequency-magnitude relation was established in different stages of the uniaxial test by the spectral analysis. For the specimen failed along the weaker bedding, the AE signals were more intense and the accumulated AE energy before failure was larger. The sandstone has three main frequency domains at around 50 kHz, 177 kHz and 266 kHz. A significant magnitude increase before peak stresses was detected for frequency at around 177 kHz. The magnitude variation and duration in 50 kHz and 266 kHz were not clear for failure along weaker bedding planes. All these results will contribute to the forecast of rock failure and the back analysis of failure modes.
An acoustic emission is defined as a transient elastic wave generated by the rapid release of energy within a material (Lockner, 1993). Both the micro-cracks forming and the crack-borders rubbing against each other can cause the acoustic emission. An AE testing is a passive and receptive technique analyzing the ultrasound pulses emitted in the moment of defects occurrence.
