The evolution of fractures in deep, weakly cemented overlying strata and the characteristics of severe and mild fracture zones

Fracture development in the overlying strata of a quarry is a key factor leading to aquifer water loss. Clearly understanding the fracture characteristics of deeply weakly cemented overburden is of significant importance for water-preserved mining. In order to investigate further the laws governing fracture evolution and zoning characteristics of deep, weakly cemented overlying strata, research methods, including theoretical analysis, numerical simulation, and engineering measurement, are employed. The calculation method of seepage velocity is derived by using the formula for the vertical permeability coefficient of the mining aquiclude. Based on the relationship between the seepage velocity of the aquiclude and the recharge velocity of the overlying aquifer under critical water conservation conditions, a quantitative formula characterizing the water-blocking capacity of the aquiclude is proposed. It is found that the variation in permeability of the aquiclude is negatively correlated with the distance from the working face. Consequently, the fracture zoning characteristics of deeply weakly cemented overburden rock, centered around the water-blocking capacity of fractured rock strata, are summarized. The simulation analysis of the evolution of fractures in overlying rock reveals that the compaction range of fractures increases as the working face lengthens. However, the overall development range of fractures remains largely unchanged. Additionally, the expansion of the tensile fracture range occurs solely in the vertical direction as mining height increases, while the compaction range of fractures gradually diminishes. Microseismic monitoring indicates higher incidences of fractures in the structural equilibrium zone and severe fracture zone, with more frequent occurrences of tensile and shear failures. Conversely, the mild fracture zone exhibits fewer occurrences of fractures.