Surrounding rock control of the retreat roadway during the final mining stage in an ultra-thick coal seam with fully mechanized top coal caving

HUANG Kai

doi:10.11799/ce202601010

Abstract：To address the severe mine pressure behavior encountered during equipment withdrawal in the retreat roadway of a fully mechanized top coal caving face in an ultra-thick coal seam,caused by unreasonable parameters for leaving top coal and support design during the final mining stage,we employed field investigation,theoretical analysis,and numerical simulation to investigate the optimal location of the retreat roadway,parameters for leaving top coal,and surrounding rock control measures.The results indicate that leaving top coal during the final mining stage markedly reduces the intensity of strata behavior at the working face.An overlying strata structure where the main roof fracture line is located above the goaf is most favorable for the stability of the retreat roadway surrounding rock.A reasonable distance for leaving top coal is 20 m,which ensures effective goaf filling and timely fracture and pressure relief of the main roof.An asymmetric support system employing zoned rock bolts and cables(Support Scheme VI)for the retreat roadway achieves interconnection of the pre-stress fields in the coal rib and roof,enabling targeted control of the surrounding rock based on the differential principle of strong versus weak support demands.Field practice demonstrates that combining an appropriate distance for leaving top coal with a scientifically designed support system yields significant control effects for the retreat roadway surrounding rock,reducing waste of coal resources and mitigating safety hazards associated with spontaneous combustion of residual coal.