Physical modelling of subsidence from sequential extraction of partially overlapping longwall panels and study of substrata movement characteristics

Field examples of subsidence from sequential extraction of overlapping coal longwall panels have shown that complex and unexpected subsidence effects can occur. Physical models, comprising sand and plaster obeying relevant similarity rules, were used to investigate the subsidence mechanisms. Displacements within the models were measured using a combination of optical transducers, photogrammetry and laser scanning. The observed results were compared with finite element models. The models demonstrate that the incremental subsidence and substrata movement profiles after lower seam extraction can be separated into three different zones. These zones undergo different horizontal and vertical movement characteristics. The zone of overlap of the two longwall panels undergoes greater total subsidence compared to a single seam of equivalent thickness. The limit angle of the subsidence also differs at the two ends of the lower extraction as a result of the effects of the previously mined-out area above.