Preferential flow through fissures in coal mine spoil heaps

【Objective】Preferential flow through fissures at the front edge of coal mine dumps not only influences hydrological processes but also increases the risk of collapse and landslides. Understanding the factors that affect preferential flow can improve soil heap management and facilitate vegetation restoration. This paper experimentally investigates these factors.【Method】The experiment was conducted at the Shenglidong Open-Pit Coal Mine, Inner Mongolia. Field investigations, dye tracing, and digital imaging were employed to examine the distribution, migration, and dynamics of preferential flow.【Result】Preferential flow primarily occurred on both sides of the fissures, forming a ‘T’-shaped distribution near the fissures. At the soil surface, the dyed-stained area was uniform and continuous, indicating the dominance of matrix flow. As soil depth increased, both the dye-stained area and width decreased, which facilitated preferential flow. Among all fissures examined, second-category ground fissures exhibited the fastest preferential flow, characterized by the deepest dye staining and the most pronounced preferential flow under the same rainfall conditions. The dye-stained area ratios for the first, second, and third-category ground fissures were 27.23%, 31.97%, and 30.73%, respectively. This ratio decreased with soil depth, following an ‘S’ -shaped distribution. Additionally, the dye-stained area ratio varied between fissures, with ratios of 77.09%, 79.85%, and 126.17% for the first, second, and third-category fissures, respectively.【Conclusion】The dye-stained area ratio in ground fissures with smaller widths showed high variation and a dynamic pattern, enhancing preferential flow. The spatial variation of preferential flow in ground fissures was evident. These findings can help the development of strategies to improve the management and vegetation restoration of soil heaps in coal mining areas.