Effect mechanism of strata breakage evolution on stope deformation in extra-thick coal seams

The mining of extra-thick coal seams features severe deformation of the stoping roadway and section coal pillars due to the large mining thickness of the coal seams and the intense movement of the overlying strata. The adjacent goaf and secondary mining disturbance in the current working face further challenge the roadway deformation control. This study explores the effect of the overlying strata structural evolution in the fully mechanized caving face of the extra-thick seam on the failure of section roadway and coal pillars. Physical analog modeling was carried out. A MatchID non-contact full-field displacement- and strain-measuring system was used to determine the evolutionary characteristics of the overlying strata breakage in the extra-thick coal seam, including the displacement variation pattern and stress/strain distribution in coal pillars. The results indicated that following the primary mining disturbance in the adjacent working face, the section roadway and coal pillars underwent initial deformation due to the primary mininginduced stress. As the mining of the current working face continued, the section roadway and coal pillars were subjected to secondary mining disturbance to the effect that the structure of the broken overlying strata gradually formed a triangular support structure. Thus, the overlying strata tilted downwards and subsided, forming a layered hanging roof structure. The additional load was then imposed on the stoping roadway and upper part of the section coal pillars. Meanwhile, the overlying strata failure caused a significant increase in the stress within the section coal pillars. Following the secondary mining disturbance, the peak stress reached a maximum of 33.62 KPa, leading to deformation and instability failure of the section roadway and coal pillars. Finally, distinctive evolutionary features of the overlying strata structure in the extra-thick and ordinary coal seams were identified, and their effect on the deformation and failure of the section roadway and coal pillars were analyzed in detail. These findings are considered instrumental in substantiating the deformation control of the stoping roadway and coal pillars in the extra-thick coal seams. (C) 2021 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Alexandria University.