Study on gas migration and air leakage patterns in goaf retaining roadways of thick coal seams with roof cutting

To address the challenges of severe air leakage in the retained roadways of thick coal seams and unclear gas migration patterns in goaf areas, which hinder effective gas control, this study investigates the 3103 workface and develops a discrete element model using particle flow code (PFC) to simulate fracture evolution and porosity distribution in the overlying strata under roof-cutting and pressure-relief mining. The PFC-derived porosity data are integrated into a COMSOL multiphysics model to enhance gas flow simulation accuracy in porous media. The study analyzes the dynamic characteristics of gas migration and accumulation in the goaf under Y-type ventilation and quantitatively assesses air leakage behavior under different air volume ratios. The primary leakage pathways are identified as positive-pressure airflow from the intake roadway into the goaf and high-concentration gas from the return side into the retained roadway. The optimal air volume ratio between the transport and auxiliary roadways is found to be 2:3, effectively reducing gas concentration in the return airway. Based on these findings, a multi-mechanism gas control system is proposed, incorporating directional drilling, fracture sealing with composite materials, adjustable wind-blocking curtains, and intelligent gas monitoring. These measures significantly reduce gas concentrations in the goaf and retained roadway, while enhancing the workface advance rate. This study offers reliable theoretical and practical solutions for gas disaster prevention and control in complex goaf environments.