Development law and characteristics of surface cracks caused by coal mining in Yushenfu mining area

Yushenfu mining area, with large scale and high intensity, is an important raw coal-producing area in northern Shaanxi, but the fragile ecological environment makes the mine geological environment problems caused by coal mining particularly relevant. To grasp the development law of surface cracks and reveal the formation mechanism caused by coal mining in the Yushenfu mining area, the typical working faces of Anshan Coal Mine, Caragana Tower Coal Mine, and No. 1 Coal Mine of Xiaobaodang in the Yushenfu Mining area were chosen as the research object to conduct the study. The results show that the surface cracks can be divided into four types: step type, extrusion uplift type, sliding type, and tension type, as well as two combination modes of collapse, trough and parallel. In the Yushenfu mining area, the spatial distribution law of surface cracks is relatively unified. The performance characteristics of surface cracks are different and negatively correlated with the ratio of mining depth to mining thickness. The surface cracks induced by very shallow coal seam mining, shallow coal seam mining, and medium-deep coal seam mining have the dynamic law of lagging mining position 1.0 m, advanced mining position 8.5 m, and lagging mining position 30.14 m, respectively, and the relationship between the lag distance of surface cracks and the ratio of mining depth to mining thickness is a polynomial function. The characteristic of the width of boundary cracks and forward slope cracks in the working face was increased until stable. In contrast to the boundary cracks, the characteristic of the width of the reverse slope fractures increases and then decreases, and the width of the cracks in the flat area in the working face increases first, then declines, and then increases. The average activity time was 3.7–7.0 days. The crack with the activity of “opening first and then closing” is controlled by the dynamic evolution of overlying rock structure, and the fracture with the activity of “only opening and then closing” and “opening first and then closing” was controlled by surface dynamic evolution. However, the activation mechanism of slope fracture is closely related to slope slip. The findings of this study can provide theoretical guidance for surface crack control and ecological restoration in the Yushenfu mining area.