Acoustic emission and failure characteristics of coal and rock under single-free-face true triaxial loading

Abstract

The airside roadway is frequently identified as the predominant site for dynamical disasters involving coal and rock. For the assurance of safety in mining zones, it becomes imperative to understand the mechanical response and energy characteristics of the coal and rock system within the airside roadway during mining processes. A triaxial static and dynamic load test system was used to conduct compression experiments on coal and rock samples under single-free-face true triaxial loading at different loading rates. The research findings are summarized as follows: (1) The damage and failure of the samples gradually propagate from the free face to the deeper sections of the samples and evident stage characteristics. Revealed that the damage mechanism was “microfracture localization – localized region development through – overall instability.” (2) A rising loading rate impedes the coal and rock's ability to make adaptive adjustments, thereby amplifying the sample's resistance against crack development, and playing a positive role in stimulating coal and rock failure, and the coal and rock system changed from progressive stable failure to sudden instability failure. The mesoscopic failure pattern gradually evolves into inadequacy and irregularity. (3) Throughout the entire failure episodes of coal and rock samples, the predominant mode of failure is tensile. However, influenced by the loading rate, the principal failure mechanism transitions from tensile to shear during the Ⅳ stage of failure. (4) There is noteworthy congruence between the macrofracture sites and the spatial positioning of high-energy fracture episodes. This furnishing pivotal insights for preempting and control deep impact disasters.