Roof fracturing in highwall mining based on CCCF thin rectangular plate model with trapezoidal load

Purpose This study aims to elucidate the role of the main roof in highwall mining slope stability under localized coal pillar failure conditions. Prior research has not adequately addressed how large-scale pillar failures propagate instability through the mechanical linkage between the pillar support system and the slope sliding system. By analyzing fracture mechanisms and crack morphology of the main roof, this model seeks to clarify its control effect on highwall mining slope stability. Design/methodology/approach A CCCF (three edges clamped, one free) elastic foundation-supported thin rectangular plate model under trapezoidal load was established to analyze main roof fracturing in highwall mining. Using the derived governing equations and a second-order central difference method, the research examined key parameters influencing principal bending moments. Findings Pillar failure width and overburden depth increase all bending moments. Greater thickness and elastic modulus of the main roof amplify |M|z but reduce |M|c and |M|t, while higher foundation stiffness decreases |M|z and increases others. Three fracture sequences were identified, forming a horizontal “U-Y” pattern: U-shaped fractures develop around pillar failure zones, while Y-shaped fractures occur within failed pillars. Originality/value The mechanical model considers the CCCF boundary conditions, as well as the trapezoidal loads, and simplifies the edge of the coal pillar as Winkler elastic foundation to consider its mechanical effects. Validation through a case study demonstrated the model's accuracy in predicting fracture behavior aligned with actual mine pressure observations. The mechanical model and calculation method provide reliable theoretical support for assessing roof stability in similar engineering scenarios.