The development mining-induced surface cracks in shallow coal seam through double-gully terrain: a case study in a coal mine

Surface cracks induced by the mining of shallow seams in the gully region seriously threaten mining safety and ecological stability. This paper selected the An-shan coal mine as a typical field prototype to study the initiation and evolution characteristics of surface cracks during the mining process of shallow coal seams in the double-gully region. Based on the field-collected data, the finite difference method model, the scaled laboratory physical model with similar materials, and the analytical model of the field prototype were constructed. Combined with numerical simulation and physical model test results, the initiation locations relative to the excavation faces and the width and faulting features of mining-induced surface cracks were comparatively analyzed. The new function (T) integrating topological parameters of double gullies and its determination criterion were then proposed to locate mining-induced surface cracks relative to the excavation face in the shallow coal seam underneath the double-gully terrain. It was revealed that the positions of surface cracks relative to the excavation face were greatly affected by the depth, slope angle, span, and other features of the gullies, among which the gully slope angle was the main influencing factor. Both T and vertical bar T vertical bar values were correlated with the relative position of surface crack to the excavation face, crack width, faulting level, and the total number of cracks in the single-gully region. The proposed function (T) could predict accurately from valley parameters the relative positions of surface cracks induced by the mining of shallow coal seam in gully regions.