Support-load response and mining-induced stress evolution in a deep extra-thick coal seam under single-pass full-height longwall mining

Abstract To clarify the intrinsic relationship between overburden structural instability and strata behavior during single-pass full-height extraction of a deep extra-thick coal seam, this study investigated Panel 140,504 of the Kouzidong Coal Mine using an integrated approach that combined in situ strata-pressure monitoring, theoretical analysis of overburden fracture, and FLAC3D numerical simulation. Variations in shield working resistance, main-roof fracture characteristics, and the mining-induced stress field were systematically examined as the face advanced. The results showed that shield working resistance remained at 18–20 MPa during the initial mining stage but increased rapidly after immediate-roof caving, reaching a peak of nearly 40 MPa. As the exposed span of the main roof increased, first weighting occurred after the face had advanced approximately 32.5 m. During normal retreat, shield working resistance exhibited pronounced periodic fluctuations, with a mean periodic weighting interval of approximately 13.8 m. Theoretical calculations based on multi-stratum equivalent-load transfer and an elastic-foundation beam fracture criterion yielded first- and periodic-fracture spans of 32.5 and 13.27 m, respectively. The relative error between the calculated and measured periodic weighting intervals was only 3.70%, supporting the applicability of the theoretical model. The FLAC3D simulations showed that, as the face advanced, the mining-induced stress field evolved through four stages: stress relief within the goaf; stress concentration ahead of the face and along both sides of the goaf; formation of an arch-shaped load-bearing structure in the overburden; and stabilization of the high-stress zones. The plastic zone first developed in the weak immediate roof, then propagated into the main roof, and eventually formed a stable, vertically zoned failure pattern. Strong strata behavior under these conditions was jointly governed by immediate-roof caving, periodic main-roof fracture, and compaction of the caved material in the goaf. Shield working resistance, overburden stress redistribution, and plastic-zone expansion exhibited clear stagewise correspondence. These findings provide a theoretical basis for roof control and shield-support parameter optimization in longwall panels with comparable geological and mining conditions.