Simulation Analysis of Creep Evolution Process in Soft-Hard Composite Coal Seams

To address the coal and gas outburst risks in the soft-hard composite coal seam, a three-dimensional (3D) model of the soft-hard composite coal seam of Hudi Coal Mine in China was constructed, incorporating coal creep effects.The influence of punching parameters (diameter, spacing, direction, and creep duration) on stress-damage evolution, pressure-relief range, and gas seepage behaviour in the coal seam was analysed.Results revealed that under the viscoelastoplastic model, creep deformation in soft coal zones expanded the pressure-relief range by approximately 30 % compared to elastoplastic models, with more stable gas seepage pathways.Directional punching along the maximum principal stress direction induced oriented fracture propagation, improving pressure-relief efficiency by over 25 %.Key parameter findings include: a critical punching diameter of 1.5 m (beyond which collapse risks increase), optimal spacing of 6.0 m, and stabilized pressure-relief effects after 40 d of creep.This study provides a theoretical basis for enhancing hydraulic punching efficiency and gas drainage performance in soft-hard composite coal seams.