A capillary barrier cover (CBC) is a geotechnical structure which a coarse-grained soil layer covered by a fine-grained soil layer. A CBC can retain downward water infiltration, increase water storage capacity and lateral diversion, and prevent capillary rise. Geotextiles are usually set up as isolation layers between fine-grained and coarse-grained layers to prevent fine particles entering the coarse-grained layer, resulting in a decrease in downward water infiltration and water storage capacity. However, crustal stress, farming, animal, plant activities, and other factors may cause damage to the isolation layer. At present, there is no reliable and accurate method to determine the location and degree of damage to the isolation layer. The existing methods search for the damage location by excavating the whole fine layer, which incurs high maintenance costs. If the damaged position of the CBC isolation layer can be accurately obtained, it can reduce maintenance costs. Therefore, this study investigated the influence of a coarse-grained layer mixed with different particle sizes and proportions of fine particles on water storage capacity through laboratory soil column experiments. The results are as follows: (1) Fine particle mixing into the coarse-grained layer will reduce water storage capacity, and there is a worse admixture ratio that minimizes water storage capacity. (2) The CBC enhances the fine-grained layer volumetric water content (VWC), but the enhancement degree decreases as the distance from the fine-coarse interface increases. (3) A method has been proposed to determine the location and degree of damage to the isolation layer. When the VWC at the fine-coarse interface reaches a stable level during breakthrough, the CBC effect exists, the higher the VWC at the fine-coarse interface, the stronger the CBC; when the VWC at the fine-coarse interface is unstable during breakthrough, the CBC effect disappears, and the median diameter of the fine particles mixed into the coarse-grained layer is finer than or equal to the fine-grained particles' median diameter.

The process of rainwater infiltration into unsaturated multi-layered slopes is complex, making it extremely difficult to accurately predict slope behaviors. The hydrological mechanisms in multi-layered slopes could be significantly influenced by the varying hydraulic characteristics of different soils, thus influencing slope stability. A numerical model based on Hydrus 2D was constructed to investigate the hydrological mechanisms of multi-layered slopes under different slope inclinations and rainfall intensities. The results revealed hydraulic processes in response to rainfall in unsaturated multi-layered slopes, in which layered soils retard the advance of wetting fronts and affect seepage paths in the slope. The results also showed the characteristics of hydraulic parameters, including pore water pressure and moisture content, under different conditions, and explained the crucial factors at play in maintaining slope stability.

In response to the rapid urban expansion and the burgeoning number of landfill sites, managing water infiltration in these areas has become a critical challenge, especially in cities like Shenzhen, Hong Kong, and Singapore where traditional cover materials such as silt, clayey gravel, and sand are scarce. A three-layer (silt/gravelly sand/clay) capillary barrier cover system has been proposed to address this issue in humid climates. As an alternative to scarce traditional materials, using local soils and construction waste (CW) for this system presents a viable solution. However, the real-world performance of this adapted three-layer system, constructed with local soils and CW under natural rainfall conditions, remains to be fully evaluated. This paper presents a field test evaluating the water infiltration behavior of a three-layer capillary barrier landfill cover system under natural conditions. The tri-layered system is comprised of a 0.6 m loose local unscreened soil layer, covered by a 0.4 m CW layer and topped by a 0.8 m heavily compacted local screened soil layer. Monitoring findings reveal that, during the wet season, infiltration through the top two layers was staved off until the third rainfall, after which these layers retained moisture until 15 September 2016. The fluctuation in pore water pressure in the topmost layers showed each rainfall was contingent not only on the day's precipitation but also the hydraulic state. Beyond the hydraulic state's influence, a deeper tensiometer showed resulted in a diminished correlation between the surge in pore water pressure and daily rainfall. This declining correlation with depth can be attributed to the capillary effect and the reduced permeability of the screened soil layer. Rainfall patterns significantly affect percolation, with the combination of a short-duration, intense rainfall and prolonged weak rainfall resulting in a marked increase in percolation. In the foundational screened soil layer, the pore water pressure remained relatively low, with the cumulative percolation over six months (June to December) registering approximately 10 mm. These findings suggest a promising performance of the three-layer capillary barrier cover system, integrating local soils and CW, in the year of the study conducted in a humid environment.

Mine site reclamation is a major concern for mining companies, especially when mine tailings are potentially acid generating mine drainage. For mine sites located in Arctic environments, many factors, such as climate change, the evolution of permafrost, remoteness, the availability of materials, and harsh climatic conditions, can make difficult the implementation of conventional rehabilitation methods. Therefore, it is necessary to design and develop reclamation approaches specific to these conditions. This study focuses on assessing the effectiveness of covers with capillary barrier effects, made of desulphurized tailings from Raglan mine (Nunavik region, Quebec). The approach would mitigate the risk of water contamination by simultaneously limiting oxygen migration into potentially acid-generating tailings, as well as reducing their temperature. The study involved a detailed characterization of the cover materials and the construction of two instrumented columns in a controlled-environment chamber (two residual sulphide level). Column tests demonstrated that capillary barrier effects induced a permanent high degree of saturation (>85%) in the moisture-retaining layer made of desulphurized tailings. This high degree of saturation impeded oxygen migration; the estimated oxygen fluxes passing through the moisture-retaining layer being lower than 5.5 x 10(-3) mol/m(2)/day for the two columns. The column containing the desulphurized tailings with the highest sulphide content was slightly more efficient in controlling the oxygen flux due to the greater oxygen consumption by residual sulphides. Results also showed that freeze-thaw cycles did not significantly affect the hydrogeological properties of the desulphurized tailings, thus indicating a stability in the long-term performance of the cover. (C) 2018 Elsevier Ltd. All rights reserved.