In extremely thick coal seam mining, residual coal pillars and associated goafs induce asymmetric instability in underlying roadways, leading to severe floor heave disasters. Unlike previous studies that rely on single stress parameters, this study integrates deviatoric stress invariants J 2 and J 3 with unloading damage mechanics to evaluate roadway stability, where J 2 reflects the magnitude of shear stress concentration and J 3 identifies the dominant failure mode, distinguishing between compression-dominated and extension-dominated stress states. A theoretical stress model incorporating the combined effects of residual coal pillars and adjacent goafs was developed. Triaxial unloading experiments demonstrated that unloading trajectory, rather than final stress state, controls progressive damage evolution. Numerical simulations of four roadway layouts revealed symmetric Y-shaped high stress zones beneath pillar goaf interfaces, and a coal pillar spanning roadway layout (CPSRL) was proposed with the lowest stress concentration and damage indices. A multilevel support system combining surface shotcrete, deep grouting, and active–passive reinforcement was implemented.
Wang et al. (Sat,) studied this question.