Temporal-Spatial Evolution of Acoustic Emission in Raw Coal with Pre-Fabricated Roadway: An Experimental Study for Mining Geomechanics

Roadway surrounding rock stability under high in-situ stress is a core challenge in mining geomechanics. This paper presents an empirical and analytical study on the temporal-spatial evolution of acoustic emission (AE) during fracture of raw coal specimens with a pre-fabricated simulated roadway. A true triaxial loading system was adopted to reproduce two typical stress paths, i.e., vertical loading coupled with lateral unloading and pure vertical loading, to mimic the stress redistribution characteristics induced by deep roadway excavation and subsequent mining disturbance. AE event counts, time-frequency features, 3D source locations and energy distributions were synchronously acquired via a 24-channel monitoring system. Results show that notable stress concentration zones form around the pre-fabricated roadway under both stress paths, while the instability modes present significant differences. Under the vertical loading coupled with lateral unloading path, macroscopic instability lags over 150 s behind the AE activity peak, exhibiting clear precursor characteristics. In contrast, under the pure vertical loading path, local abrupt instability occurs without obvious abrupt change in AE event counts, showing typical sudden brittle fracture characteristics. Prior to failure, AE energy and amplitude fluctuate sharply and the dominant frequency shifts to high-frequency bands, serving as quantitative indicators for accelerated fracture. Fractures initiate from the borehole wall and expand radially; high-energy AE zones align well with major fracture paths. These findings provide experimental support for fracture early warning and surrounding rock stability evaluation in deep coal roadways, and offer reference for mining geomechanical design and ground support optimization.