Height of the mining-induced fractured zone above a coal face

The development height of a gas conducting fracture zone (GFZ) in the gob overlying strata is crucial to the gas drainage and safe production of a coal mine. In order to address the issues of excessive gas concentration and uncertain GFZ height in No. 7435 Face overlying strata of Kongzhuang Coal Mine, China, the caving characteristics of overlying strata were explored using both physical experiments on similar materials and numerical simulations of Particle Flow Code (PFC) software and verified each other. The relationship of cracks development to porosity changing characteristics was introduced to quantitatively determine the height of the local GFZ. The quantified GFZ heights were compared with those measured using the in-situ drilling flow method. The results showed that 1) PFC software could accurately simulate the overlying strata caving behaviors, thus saving manpower, materials and financial resources needed for related physical experiments, and 2) the temporospatial distribution characteristics of porosity could be used to forecast GFZ height, and are of significant importance for determination of GFZ. Overall, the conclusions are of engineering significance for accurate arrangement of boreholes for gas drainage and reduction of mine gas disasters.