Frequency properties of acoustic emissions from the dry and saturated rock

Abstract

Different frequency bands (FBs) of acoustic emission (AE) signals from rock fractures contain diverse information about the physical and mechanical properties of a rock. This study proposes a frequency division processing method for the standard description expressions of discrete signals and for defining the integrated characteristics of AE signals. The frequency evolution of rock fracture-related AEs was investigated under uniaxial loading conditions, and rocks in dry and saturated states were examined and compared using AE information in FBs. The correlation between the water state and FBs of AE signal was addressed. The FB features (e.g., energy concentration) were analyzed, and their changes in water conditions were also considered by focusing on the FBs with the greatest energy concentrations. During rock fracturing, dry and saturated samples developed various shear-tensile damage patterns or “rock bridge” modes. The moisture property of rock affected the peak strength, plastic deformation, and intensity of the rock destruction, and the statistical relationship observed between rise time/amplitude and average frequency showed that the crack characteristics depended on the presence or absence of moisture. The most suitable FB to distinguish the water state was 31.25–62.5 kHz. The parameter ζ (i.e., variable energy coefficient) exhibited a sudden increase in the FB of 0–31.25 kHz. This rapid change was more remarkable than that in the other FBs. This FB should be considered useful for monitoring to help predict the final rupture. The method developed here provides a new way for examining the rock damage characteristics and discovering the fracturing behavior patterns.