Exploration and prediction evaluation on causative factors of water inrush from separation layers of mining overburden in coal mines

The occurrence of mine water inrushes is common and poses significant hazards in various mining areas throughout China. However, the existing regulations lack of specific engineering geological and hydrogeological exploration guidelines tailored to the water inrush from separation layers (WISL). Exploring the methods of engineering geological and hydrogeological exploration and assessment for the WISL can contribute to further enhancing the prevention and control of mine water disasters in China. This paper begins by examining the mechanism behind WISL in coal mines. It analyzes the geological conditions governing the progression of WISL from its inception to full-scale occurrence and categorizes three prevalent types of WISL in China, i.e., dynamic water inrush, hydrostatic water inrush, and mud and sand-carrying water inrush, all originating from separation layers. Subsequently, it identifies “water source”“channel”“force source”and “material source” as pivotal concealed factors dictating the nature and severity of WISL. Then, the concept of a “inrush separation zone” referring to composite stratigraphic layers situated above traditional water-conducting fractured zones is introduced, where the WISL may transpire during mining activities. Furthermore, it presents a method for delineating “inrush separation zone” in coal mines, outlining exploration stages and specifying crucial investigative focal points. The exploration of water damage in upper strata of coal mine should include two stages: first, the exploration of basic engineering geology and hydrogeological conditions of overlying rock should be carried out to evaluate the possibility of water damage in the exploration area and determine the horizon of potential mining overlying rock ; second, regarding the “inrush separation zone” and “source” layer as the exploration target layer, the special investigation of the hidden disaster factors of the upper layer water damage should be conducted to assess the type and intensity of the water damage in the upper layer. The hydrodynamic conditions and the evolution of overburden fractures are investigated during the mining period. Lastly, a comprehensive forecast evaluation model is proposed and constructed on the coordinated evolutionary mechanisms arising from the interaction of causative factors like “water source”“channel”“force source”and “material source”. This model predicts and evaluates the types, locations, and inflows of water inrush at mining faces before operations commence.