Influence Characteristics of Double-Stratum Hard Roof Movement in a Fully Mechanized Top Coal Caving on the Working Resistance of Supports

Abstract

In the traditional mechanical models of hard roof, multiple hard rock strata are usually taken as the overall critical stratum to analyze its movement instability characteristics while the mutual effect between two hard rock strata is neglected, so it's difficult for theoretical analysis results to realize the accurate prediction of mine pressure behaviors. The reasonable prediction of mine pressure behaviors on a fully mechanized caving face with multiple hard rock strata is ensured further by considering the geological conditions of the 1307 working face mine in Zhaoxian Coal Mine in the Yonglong Coalfield Mine area in China, a mechanical model of a hard roof structure with high and low strata (double strata) was proposed in this study, and the periodic instability step of the high-and low-level hard roofs and the change laws of support resistance on the working face were also determined. Then, the theoretical calculation results were verified according to field measurement data. Results indicate that fracturing instability does not simultaneously occurred in the high and low strata of the hard roof, as the instability steps are 106 m and 18 m, and the corresponding working resistances of the hydraulic support are 63 MPa and 37 MPa, respectively. Meanwhile, the onsite-measured mine pressure data suggest that the major-cycle cyclic weighting step is approximately 101 m, while the continuous step is approximately 12 m. The minor-cycle cyclic weighting step is within 15-25 m, the continuous step is approximately 2 m, and the peak working resistances of the hydraulic support on the average are 42.3 MPa and 36.8 MPa, respectively, so the on-site monitoring data basically accorded with the theoretical analysis results, thus verifying the scientificity of the constructed mechanical model. This study provides a theoretical reference on the safe mining of the fully mechanized caving face of a multi-stratum hard roof.