Quantitative Evaluation of the Structure and Coal Thickness Stability of the Thin Coal Seam in Lucun No. 2 Coal Mine, Yan’an

Coal mining under thin seam conditions puts forward higher requirements for accurately understanding the spatial variation law of coal thickness and structure. A thin coal seam was developed in the north of the Huangling mining area in Yan’an, Shaanxi Province. However, the structural characteristics and spatial variation of coal thickness are not well understood, which restricts efficient coal mining and intelligent mine construction. In this study, the No. 2 coal seam, a thin coal seam mined in Lucun No. 2 Coal mine in Yan’an, was taken as a research object. Based on the elevation data of the coal seam floor, trend surface analysis and structural curvature analysis were carried out to reveal the characteristics of structural development. The variation coefficient of coal thickness of 775 grid nodes was calculated based on the mesh splitting method to reveal the variation rule of coal seam thickness and its stability zoning. It will overcome the deficiency of the traditional single evaluation value of coal thickness variation coefficient to reveal the spatial change of coal thickness stability. The results showed that the No. 2 coal seam belonged to a relatively stable coal seam with a monoclinal structure trending NE and inclining NW. Under this background, secondary undulation with a NW axis was superposed. Three new typical structures were identified, namely, a local depression developed in the northeast part of the coal mine, a local dome developed in the north-central part of the coal mine, and a saddle shaped structure developed in the south of the coal mine with a NW-SE direction. In the northern part of the saddle shaped structure, several faults discovered during coal exploration and mining were superposed, which made the structure in the southern coal mine relatively complicated. The variation coefficient of coal thickness ranged from 0.16% to 15.24%, with an average of 1.98%. The variation coefficient of coal thickness gradually increases from north to south and reaches the maximum value near the Boreholes 12-7 and 12-8 in the southwestern coal mine. Within the recoverable area of coal seam, the thickness stability of coal seam gradually deteriorated from northeast to southwest. The saddle shaped structure was highly consistent with the high value area of coal thickness variation coefficient. Based on the classification of coal thickness and coal thickness variation coefficient, six combination schemes of coal thickness and stability were identified, and a partition evaluation of coal thickness and stability was realized. It revealed that the mining conditions in the eastern part of the recoverable area were better than those in the western part, with the worst occur in the southwest. The change of coal thickness was exacerbated by the saddle shaped structure. The research results would provide geological support for safe, efficient, and accurate mining of thin coal seam.