Study on the Stability of aquiclude in the Close-Distance Coal Seams Repeated Mining in the Jurassic Coalfield of Northern Shaanxi

The aquifer in the Salawusu Formation is extensively distributed within the Jurassic coalfield of northern Shaanxi, China. However, the fracture development in overlying strata induced by repeated mining of close-distance coal seams and the stability of the aquiclude remain unclear. Combining the methods of statistical analysis, numerical simulation, and theoretical analysis, the stability criterion of the aquiclude was established. Results show that for single coal seam mining, the development height of mining-induced fractures is proportional to the mining height. In contrast, the ratio of fracture development height to mining height (r) shows no significant correlation with the mining height, typically ranging from 18-30. For repeated mining of close-distance coal seams, the r also exhibits no obvious correlation with the cumulative mining height, with a typical range of 10-25, which is lower than that observed in single-seam mining. The calculation methods for the development height of upward fractures and the development depth of downward fractures during repeated mining were given, and the stability criterion of aquiclude based on the development characteristics of mining-induced fractures is proposed. The research outcomes further enrich the strata control theory for water-preserving mining of close-distance coal seams in western China.