Strong strata behavior mechanism and roof cutting control of small pillar gob-side roadway in extra-thick coal seam

In Datong mine, the extraction of coal resources faces challenges due to strong strata behavior and significant deformation of gob-side roadways during working face extraction. To address these challenges and control major surrounding rock deformation, wide pillar, design, robust support systems, hydraulic fracturing, and roof cutting by explosives are often employed. To further improve safety and efficiency, this article proposes the application of carbon dioxide phase transition fracturing (L-CO₂) for roof cutting in small pillar gob-side roadways. Field investigation, theoretical analysis, numerical simulation, and on-site tests were conducted to evaluate the performance of the proposed scheme. The results indicate that the main roof break position is approximately 6.8 m from the coal wall on the gob side. It is observed that after roof cutting, the second deviatoric stress invariant (J₂) of the overlying rock strata shifts about 5 m into the solid coal side. The peak J₂ of surrounding rock is reduced by approximately 150 MPa² for the roof and around 20 MPa² for the roadway sidewalls. The peak third invariant (J₃) shifts about 10 m away from the roadway. Through on-site testing, fracturing parameters were determined and a L-CO₂ control scheme was developed for small pillar gob-side roadways in extra-thick coal seams. The proposed scheme was validated through field applications.