In situ dynamic monitoring of stress revolution with time and space under coal seam floor during longwall mining

In situ dynamic monitoring was used to obtain spatial and temporal strain and stress data in the floor strata during longwall mining at the no. 1604 working face in Nantun Coal Mine, China. The results reveal the presence of four stress stages distributed at four sections along the mining direction: weak response stage, significant increase stage, dramatic decrease stage, and slow restoration stage. Three vertical structural zones are identified under the excavation floor: (1) fracture zone, (2) deformation zone, and (3) lightly affected zone. Based on detailed analysis of the collected data, the relationship between the maximum vertical stress increment and depth is inversely exponential, whereas the relationship between the maximum horizontal stress increment and depth is linear. The monitoring results are conducive to determining the maximum depth of fracture zone under the coal seam floor and width of the significant stress increase stage, which are important factors in controlling groundwater inrush in operating coal mines.