Mechanism and control strategies for asymmetric floor heave in extra-thick coal seam roadways under high stress

To address the intense stress evolution and severe floor heave in roadways of extra-thick coal seams, this study investigates the catastrophic evolution laws and mechanisms of medium-hard floor strata using the 122,110 working face of Caojiatan Coal Mine as the engineering background. By integrating field monitoring, theoretical analysis, and numerical simulation, the research challenges the traditional perception of damage caused by a single load and reveals that the "low-level stepped rock beam + high-level articulated rock block" composite load-bearing system, formed after mining, is the root cause of the extreme stress imbalance between the coal pillar side and the solid coal side. The study identifies the non-symmetric evolution characteristics of the roadway driven by a "non-symmetric stress gradient": the stress on the coal pillar side (26.62 MPa) significantly exceeds that on the solid coal side (22.07 MPa) by approximately 20.6%. This imbalance results in an average maximum floor heave of 473 mm, with the peak heave position shifting markedly toward the solid coal side. A mechanical model and criteria for the non-symmetric stress gradient under the influence of lateral overburden structures were constructed. The dynamic process of "high-pressure extrusion" and its coupling with non-symmetric shear paths in the floor rock mass-driven by the intense "stress potential difference" between the central destressed zone and the high-stress zones on both ribs-was elucidated. Consequently, a synergistic control theory featuring "pressure relief at the structural source, blockage of the stress transmission path, and non-symmetric reinforced support" is proposed. These findings provide a novel theoretical perspective and technical support for managing floor heave in high-stress roadways of extra-thick coal seams.