Investigation of acoustic events during shear loading of layered rock bridge; Particle flow code approach

Abstract

Abstract This research investigates acoustic emission (AE) phenomena during shear failure of layered rock bridges under different normal stresses using experimental punch tests and numerical simulation. Firstly, particle flow code (PFC) was calibrated by UCS and Brazilian experimental test results and then the shear behavior of the numerical model was verified by experimental punch test outputs. Finally, acoustic phenomena during shear failure of layered rock bridges were discussed. Rectangular specimens were utilized, incorporating a combination of different layers. These layers included a pairing of soft and hard materials, as well as variations such as a two-layered model comprising hard gypsum and soft gypsum. Furthermore, three-layered models were examined, featuring a soft interlayer in one case and a hard interlayer in another. Additionally, a four-layered model was employed for the investigation. In each model, two vertical edge fissures were introduced, with fissure lengths set at 20, 40, and 60 mm. The angle between bedding layers and shear loading direction was 90°. The results indicate that cracks initiate at the notch tip and propagate vertically until they meet the upper boundary. The frequency of significant Acoustic hits is tied to factors like crack initiation and material properties. Increasing the number of layers in the specimen leads to more Acoustic hits. The sequence of Acoustic hits between major hits is influenced by parameters such as bedding number and material properties. This correlation is attributed to different gypsum types on the shear surface. The findings from numerical bedding models mirror those from physical samples.