Gas migration control in goaf with double roof cutting and retaining roadway.

The behavior of gas migration in goaf under double roof cutting conditions directly influences the effectiveness of gas control measures. This study employs a combination of numerical simulation and field verification to investigate the patterns of gas migration and accumulation in goaf and to develop coordinated gas control methods under the conditions of double roof cutting and retained roadway. The results indicate that with double roof cutting, goaf permeability generally increases from the interior towards the exterior, with significantly higher porosity in the separation range compared to other areas. High permeability channels form along the sides of the open-off cut, the working face, and the two roadways, subsequently becoming areas of gas accumulation. High-level directional long borehole drainage achieves the best gas drainage at the bottom of the goaf on the working face and belt roadway sides, reducing gas concentration in the working face space to below 0.5%. Pipe jacking extraction along the retained roadway effectively reduces gas concentrations on the working face side and both roadway sides, maintaining working face gas concentrations consistently below 0.3%. Supplementary cutting hole drilling and extraction post-goaf formation show optimal gas extraction results on the working face side and near the two roadways, with gas concentration in the upper corner and return airflow remaining below 0.3% and trending downward. Field data validate the numerical simulation experiment theory.