Longwall mining-induced weighting mechanism and its interactions with shield support and coal wall

Purpose. Rock mass surrounding an underground space, especially in the case of longwall mining, may experience severe instabilities if the overburden facilitates a weighting event. This paper presents a detailed study of the longwall mining-induced weighting mechanism and its interactions with shield support and coal wall. Methods. Using the real-time monitoring data of shield and geological-mining conditions, this paper develops a panel-scale DEM model of longwall retreat to understand the mechanism of mining-induced weighting better. Findings. The study clearly details the profiles of horizontal and vertical stresses in the main roof strata. During periodic weighting, a re-concentration of horizontal stress at the clamped end of the cantilever roof beam is demonstrated, reaching a peak of 1.5 times the pre-mining value. Apart from the primary breaking at the clamped end, a cantilever roof beam may experience a secondary breaking near its middle. Within the main roof, the intact rocks were found to fail in tension, while the geological structures mostly failed in shear. Originality. The study reveals that while an increase in shield stiffness and yield force delays the occurrence of the weighting event, the associated longer span of voussoir/cantilever roof beams increases the coal block detachment at the wall. In contrast, an increase in the set-to-yield ratio of the shield shortens the weighting intervals, and this accordingly decreases the coal wall detachment. For coal seams, stiffer coal and stronger coal delay the occurrence of weighting. The stiffer coal, meanwhile, clearly improves coal wall stability despite the negative impact from the greater weighting interval. A faster longwall retreat rate also improves coal wall stability while delaying the occurrence of weighting. Practical implications. The findings of this paper assist engineers in better identification and response to geotechnical hazards in underground space, maintaining a safe workplace, and minimising environmental impact.