Laboratory Investigation into Coarse-Grained Layer Mixing Fine Particles with Different Soil Types and Proportions on Water Storage Capacity of Capillary Barrier Cover

Capillary barrier covers (CBCs) have gained widespread application as engineered surface layers in landfill systems, agricultural water retention infrastructures, and slope protection designs due to their superior water storage capacity and lateral drainage characteristics. The water storage capacity and lateral diversion are mainly controlled by the difference in water entry values between the fine-grained and the coarse-grained layers; However, uneven settlement during the stacking, transportation, construction, and trasportation of coarse-grained layer, as well as agricultural activities and erosion by animals and plants, may all lead to fine particles entering into coarse-grained layer, affecting the water storage capacity and even causing capillary barrier cover to fail. Therefore, this study investigated the influence of coarse-grained layer mixed with different types soils and proportions on water storage capacity through laboratory soil column experiments. The results indicate that (1) A rapid assessment method for the failure of CBC has been proposed, based on the variation pattern of volumetric water content (VWC) at the fine-coarse grained layers interface. (2) An effective CBC can be formed when the saturated hydraulic conductivity of the coarse-grained layer is at least one order of magnitude greater than that of the fine-grained layer. (3) When the mixed fine particle size in the coarse-grained layer is smaller than the fine-grained layer particle size, the CBC’s water storage performance is only affected by the proportion of fine particles added but is independent of the soil type in which the fine particles are added.