Research on overburden structure of large mining height working face in shallow seam

Based on the overburden conditions of Shendong and Northern Shaanxi coal bases, through the statistical analysis of the measured roof weighting characteristics and overburden caving height in large mining height working faces, combined with physical simulation tests, the overburden caving characteristics of large mining height working faces were studied, and the definition of the equivalent immediate roof for large mining height working faces was proposed. According to the filling degree of the equivalent immediate roof to the goaf, the roof structure was divided into fully filled type and non-fully filled type, and the static load of the short cantilever beam structure of the equivalent immediate roof on the working face support was analyzed. The study shows that the single key stratum of the overburden in large mining height working faces generally forms a “high position oblique step voussior beam” structure, and the sliding instability of this structure is the main cause of strong weighting in the working face. After the failure of the lower key stratum in the double key strata of the overburden in large mining height working faces, a stable “voussior beam” structure or an “oblique step voussior beam” structure prone to sliding instability can be formed, while the upper key stratum generally forms a “voussior beam” structure. That is, the double key strata of the overburden forms a “double voussior beam” structure or an “oblique step voussior beam-voussior beam” structure, with the more common “oblique step voussior beam-voussior beam” structure causing intense pressure. The synchronous and asynchronous instability of the key blocks in the upper and lower key strata are the causes of large and small periodic weighting in the working face. Based on the “oblique step voussior beam-voussior beam” roof structure model for large mining height working faces, a theoretical calculation method for the working resistance of the working face support was proposed and verified by engineering cases, which can provide a theoretical basis for roof control and support selection in large mining height working faces.