Mechanism and control of asymmetric floor heave in thick-seam gob-side roadways with staggered-elevation negative coal pillar layout

Asymmetric floor heave in gob-side entries of thick coal seams is controlled by rib-to-rib vertical-stress imbalance acting together with in-situ horizontal stress. We propose a layout-first mitigation strategy in which, under a staggered-elevation mining scheme, the gob-side roadway is sited as a negative coal pillar within a low-stress trapezoidal coal mass protected by the hinged semi-arch formed by key block B. A Rankine-based limit-equilibrium model is developed to quantify the active–passive slip mechanism of floor failure and to rank the sensitivity of key parameters. UDEC numerical simulations and 1:100 physical similarity tests are then used to resolve the associated stress redistribution, showing outward migration of peak abutment stress, a widened low-stress belt, and a transition from deep, through-going floor damage to shallow, segmented damage. To enable reproducible comparisons across layouts, three dimensionless indicators (Sf, Rpeak, and D) were introduced, together with a lightweight statistical workflow. Field monitoring on two adjacent panels at the Zhenchengdi Mine further verified the effectiveness of the NCP layout. Compared with the conventional gob-side roadway with a 20 m coal pillar, the NCP layout increased the roadway-to-peak distance to about 12.6 m, widened the rupture-zone width to about 7.8 m, reduced surrounding-rock convergence, and prevented observable floor heave within the monitored advance. These results indicate that the sidewall stress-concentration factors (K, K′) have a stronger influence than the lateral pressure coefficient (λ).