Discussion on overburden zoning model after mining and its engineering significance

The mechanical state of overburden after mining is directly related to roof accidents and roof water disasters, so it is necessary to study the overburden structure after mining. The "New Four Zones" model of overburden structure is proposed: caving zone, fracture zone, bedrock separation zone and loose alluvium zone. Combined with the previous "Three Zones" model and "Four Zones" model, this paper makes a spatial comparative analysis to clarify the spatial relationship of the three zoning models. It discusses the scientific nature of the "New Four Zones" model in terms of the influence of mining on water level of the aquifer in the overlying strata, optical fiber detection, roof water drenching, etc., and comes to the conclusion that any interval in the overlying bedrock of the coal seam may produce separation fissures(called separation spaces when reaching a certain macro scale). The "Three Zones" model is mainly used to check the rated working resistance of coal mining supports and to guide the design of water proof coal(rock) pillars. The "Four zones" model can guide the grouting engineering practice in the separated zone to a certain extent, but it has disadvantages of the safety risk of underground grouting and weakening the original engineering value of the "Three Zones" model. The "New Four Zones" model builds on the engineering significance of the "Three Zones" model, and can effectively guide the prevention and control of roof separation water disaster.