Formation and dynamic transition of the stacked beam-arch structure in overlying strata during thick-seam mining

The mechanical behavior and fracture evolution of overlying strata during thick-seam mining directly govern stope stability, mining-induced pressure, and surface subsidence. However, existing static structural models often fail to reconcile with the dynamic nature of mining processes. This study systematically investigates the formation and evolution mechanisms of load-bearing structures in the overlying strata of the Shendong Mining Area. Failure criteria for overlying strata structures are established and the formation mechanisms along with evolutionary processes are elucidated. Key findings include: (1) The stacked beam-arch (SBA) structure forms through three evolutionary stages—immediate roof collapse (L ≤ 40 m), fixed-end beam fracture (40 m < L ≤ 80 m), and arch stabilization (L > 80 m). (2) The critical span of the main key stratum is 105 m, 23% longer than predictions by key stratum theory, due to the flexural constraint of underlying sandstone layers. (3) The interdependence within the beam-arch dual structure is systematically analyzed. When beam failure occurs in the stacked beam-arch configuration, three distinct failure modes emerge based on depth-span ratios. This study formulating the basis for safety factor calculations of stope overburden structures and providing a unified framework for optimizing support design and subsidence control in similar geological settings.