Background In arid and semi-arid mining areas of Northwest China, severe water loss in open-pit waste dumps and insufficient water retention capacity of shallow cover soils restrict the effectiveness of ecological restoration on abandoned mine land. Capillary barrier covers can enhance the water-holding capacity of the storage layer by utilizing the contrast in hydraulic properties at the interface between fine- and coarse-grained layers. However, the feasibility of constructing layered covers using mixtures of waste-dump slag and clay, as well as their water-regulation performance, still requires field verification. To address the demand for large-scale solid-waste utilization and improved shallow water retention in green mine construction, this study constructed cover systems with different solid-waste replacement ratios using waste-dump slag and clay, and investigated their capillary barrier effect, water storage capacity, and water retention performance.
Methods Laboratory saturated permeability tests and soil–water characteristic curve tests were conducted on soils with different solid-waste utilization ratios to evaluate the theoretical water storage capacity of the solid-waste-based cover systems. A large-scale 40 m × 40 m field test area was established in Northwest China for solid-waste-based cover systems in a waste dump. Field rainfall monitoring and water infiltration tests were carried out to characterize the infiltration behavior of covers with different mix proportions at field scale. The water storage capacity and capillary barrier performance of covers with different solid-waste replacement ratios were then compared.
Results and conclusions After rainfall, the cover with a solid-waste replacement ratio of 33% exhibited the best water storage performance, with a measured total water storage of 238.8 mm. The capillary barrier cover with a solid-waste replacement ratio of 50% achieved a measured total water storage of 202.8 mm, representing a 13.7% increase compared with the maximum water storage of the control test area. Once the capillary barrier effect was activated, infiltrated water effectively accumulated above the coarse–fine-grained interface, and the volumetric water content at the bottom of the storage layer increased by approximately 30%. Compared with covers without a capillary barrier design, the solid-waste-based cover systems showed higher water storage capacity, with effective water storage increased by 30.1%-36.3% relative to the single-layer cover. Meanwhile, downward water migration was significantly slowed, and the average post-rainfall water loss rate within one week decreased from 3.3 mm/d to 0.81 mm/d, which is more favorable for vegetation root water uptake and growth. These findings provide a reference for ecological restoration and cover design of waste-dump slopes.
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