Laws and prevention methods of ground cracks in shallow coal seam mining

The large-scale and high-intensity mining of shallow coal seams in northern Shaanxi has induced serious ground collapse, resulting in land damage in large area, water and soil loss, and vegetation death, and thus leading to the epigenetic environment degradation. In order to understand the development law of ground collapse and fracture in shallow coal seam mining, clarify its mechanism, and put forward the appropriate treatment and restoration measures to realize the coordinated development of “coal-water-ecology”, Zhangjiamao mine field and Ningtiaota mine field in northern Shaanxi were taken as the study area. On this basis, the development law and control methods of ground collapse in shallow coal seam mining were studied by means of field investigation, simulation experiment and theoretical analysis. As shown in the results, the ground fractures in shallow coal seam mining are distributed in “O” shape, and the static development characteristics are positively correlated with mining height, topography and geomorphology, but negatively correlated with mining depth. Besides, the ground fractures are most developed near the cutting hole of the same working face, followed by the roadway, and least developed in the face. The ground fracture has two characteristics of activity: “opening first and then (half) closing” and “only opening”. The activity lasts 4-9 days in general. During the activity period, the initial fracture width has a linear positive correlation with the maximum development width, and has a linear and exponential positive correlation with the stable width. The ground fracture activity of mining in the downslope section of the loess gully region is related to the stability coefficient of the topsoil block, while the stability coefficient is negatively correlated with the slope toe but positively correlated with the main fracture spacing by a first power function. The activity of “opening first and then (half) closing” of mining slope fractures in the uphill section is controlled by rock block inversion and slope slip, and the activity characteristics of in-plane gulley bottom fractures are controlled by the migration of key rock strata. In this paper, the treatment method of “fracture filling-gulley restoration” was proposed for the penetrating fractures in the bottom of gully and “fracture filling+micro-topography reconstruction” for slope fractures in loess gully region. In addition, the “three-ring” restoration mode was studied for the collapse area in sand beach. The research results have been applied in Anshan Coal Mine and Ningtiaota Coal Mine with good results. © 2023 Ezikov Svyat. All rights reserved.