Research on Stress Migration and Evolution Law of Coal in Driving Face and Generation Mechanism of Acoustic Emission

Abstract

By means of FLAC3D software, firstly 3-demensional model was built, and stress migration and evolution law of coal seam in the process of mine roadway excavation are studied. Then according to the stress evolution law, the mechanism of acoustic emission (AE) generation in coal after excavation was analyzed. The results show that: after excavation, due to lateral displacement constraints in the coal body near the free face is removed, the coal in this zone was in 2-dementional stress condition. Because the vertical stress exceeded the uniaxial strength of coal body, the coal got into the post-peak strain-softening state. With the evolution of time, the stress in the zone gradually reduced until a state of equilibrium. In this zone the principle of AE generation is that lateral stress reduction result in macro crack propagation, coal mass failure, then elastic wave emitted. Signals come from the zone, i.e. stress relief zone, is the main part of AE signals, and should be the focus of study in AE technology of predicting coal or rock dynamic disasters. In stress-peak zone, due to the constraints of the lateral displacement, the lateral stress and strength of coal increased, the vertical stress of coal body gradually increased until the strength peak in the 3-dimensional stress state. After the excavation of roadway, the stress in stress-concentration and stress-peak zone gradually increased to equilibrium state over time. The principle of AE generation in this region is that due to the increase of the vertical stress, coal and rock gradually damaged that resulted in the release of the elastic wave.