Stress change near a major geological structure during longwall mining

ABSTRACT: Stress state and geotechnical conditions often change significantly near major geological structures (e.g. faults, shear zones, dykes) in underground coal mines, which is the cause of most major mine instability and/or safety hazards including coal burst, roof falls, water inrush and gas outburst. In order to understand and quantify the stress state near major geological structures, an integrated study had been conducted in the vicinity of a dyke in an Australian underground coal mine. The field monitoring program included installing microseismic geophones, stressmeters and extensometers in the roadway roofs and coal pillars, aiming to obtain seismic and stress change data during longwall mining. The monitoring results indicate that the stress regime was clearly different on the inbye and outbye sides of the dyke. The inbye side had a much higher stress than the outbye side before and during the longwall mining. This study provided quantified field evidence that the stress concentration occurs near major geological structures. This stress concentration could lead to high strain energy concentration in the rib of a roadway, and hence increase the risk of coal burst.