Nonlinear mechanical analysis of load-bearing characteristics of coal-support-backfill system crossing abandoned roadways

Roof pre-fracture poses a considerable risk during the re-mining of residual coal above abandoned roadways, threatening the safety of the mining faces. This study employs a Winkler foundation beam model for mechanical analysis of roof structures and adopts a multivariate nonlinear analysis approach to explore the synergistic load-bearing effects within the 'coal pillar-support-backfill body' system during the fill and re-mining processes above these roadways. The findings demonstrate that backfill mining significantly reduces stress concentrations in coal pillars and reduces excessive bending moments in roofs near abandoned roadways. The roof deflection equation incorporates three critical factors affecting stability during backfill mining: the width of the coal pillar ( ), the working resistance of the support ( ), and the elastic foundation coefficient of the backfill material ( . Under single-factor conditions, the impact sequence on roof stability in the coal pillar zone is > > . Further, multivariate nonlinear analysis reveals the interactions within the 'coal-support-backfill' structure, indicating that in terms of roof control, the interaction terms are ordered as > > . Therefore, priority should be given to adjusting the coal pillar width and backfill strength, followed by modifications to the support resistance and backfill strength during the recovery of abandoned roadways. An improved understanding of these interactions will help optimize strategies for the recovery of residual coal through abandoned roadways, thereby enhancing the stability and safety of mining operations under complex geological conditions.