• Nonlinear flow in coal penetrating fractures is classified into three types: non-Newtonian seepage under high confining pressure and low JRC, non-Darcy seepage under low confining pressure and high JRC, and transitional behavior.
• Geometric parameters of fractures (effective contact ratio, aperture, void deviation ratio) change exponentially with confining pressure, with high JRC samples showing increases of up to 93.5%, 67.4%, and 24.9% under high confining pressure compared to low JRC samples.
• A new seepage model incorporating geometric parameters was proposed, achieving superior accuracy with average RMSE of 0.002 and R² of 0.70, outperforming existing models.
• The study provides a quantitative relationship between fracture geometry and stress, enabling better prediction of fluid flow in coal-rock masses for applications like gas extraction and water hazard prevention.