Optimization of gateroad layout under a remnant chain pillar in longwall undermining based on pressure bulb theory

This research presents the detailed application of pressure bulb theory in optimising gateroad layout under the remnant chain pillar of the longwall undermining technology with the assistance of numerical simulation of FLAC3D®. Prior to extracting the gateroad in the underlying seam, the threshold bulb corresponding to the minimum offset distance is determined; the optimal bulb of the maximum principle stress (MaxPS) as well as the maximum shear stress (MaxSS) predicts the optimal offset segment. After the gateroad is extracted in the subsequent seam, two indicators of the peak normalised rib abutment stress and the width of the yield zone are employed to verify the validity. For particular case of Sydney basin, Australia, the minimum offset distance suggests 31 m, while the optimal offset segment projects the range of 41–156 m. In terms of the diverse mining operation plan, the optimum offset distance is 71 and 156 m corresponding to the optimal MaxPS bulb and MaxSS bulb, respectively. The calibration result of the optimum offset distance is roughly 65 m which agrees very well. This study can provide theoretical framework of a design overview and practical basis for similar mining conditions in other coalfields.