Mechanism and Integrated Control of “Rib Spalling: Roof Collapse—Support Instability” Hazard Chains in Steeply Dipping Soft Coal Seams

Abstract

The hazard chain of rib spalling, roof collapse, and support instability occurring in steeply dipping coal seams (SDCSs) significantly threatens the safety and productivity of underground mining. A three-dimensional coal wall model was established considering the damage to the coal wall from the abutment pressure based on the new concept of the main control weak surface (MCWS) defined by the authors. Then, a support mechanical model under the conditions of a dynamic load induced by a sliding roof was constructed. Integrated control measurements based on the models above were developed and taken for the dangerous area of hazard chains in working faces. The results indicated that the dimensions of rib spalling were dominated by the shape, dimensions, and friction angle of the coal wall element. In detail, the order of the importance of the element failure factors, based on their sensitivities, was the roof load (6.33), the dip of the panel (−5.03), the friction angle of the coal (−3.24), the cohesion of the coal (−3.02), and the sidewall protecting force (−0.087). Additionally, the order of importance of the frictional sliding factors of the slip body was the MCWS cohesion (−0.293), roof load (0.213), and MCWS friction angle (−0.079). Equations for the threshold forces between supports under the support dumping and sliding limit states were obtained; the knowledge of these forces ensured support stability under a sliding roof. The support work resistance varied synchronously in different parts of the working face and remained within 2200–4000 kN, indicating that the proposed models and control measurements considered instrumental in hazard chain control in SDCSs were reliable.