Biochar is the pyrolysed biomass which has been used as a soil amendment to improve plant performance. This study aims to investigate the effects of biochar–plant interaction on soil water retention and matric suction in silty sand (SM). In total, four soil conditions, namely soil with and without tree (Schefflera heptaphylla), biochar-amended soil (BAS) with and without tree, were subjected to drying. Three replicates were considered for each vegetated soil. By adding 10% (v/v) of biochar, the optimum water content of soil increased from 12 to 17%, while the maximum dry density decreased from 1890 to 1740 kg/m3. For both bare and vegetated soils with biochar, desorption rates of soil water-retention curves were smaller than those without biochar, while there were almost no changes in air-entry value (AEV). Biochar reduced matric suction in bare soil by 35–70% and in vegetated soil by 12–36%.
To promote environmental protection and sustainability, the use of plants and recycled wastes in geotechnical construction such as landfill covers is recommended. A landfill cover field test was conducted at the Shenzhen Xiaping landfill site, located in a humid climatic region of China. The main objective was to validate the field performance of a novel vegetated three-layer landfill cover system using recycled construction waste without the need of geomembrane. Unsieved completely decomposed granite and coarsely crushed concrete was used for the top and intermediate layers while sieved completely decomposed granite was used as the lowest layer. One section was transplanted with Bermuda grass while the other section was left bare. To assess the landfill cover performance, pore-water pressure, volumetric water content, percolation, and atmospheric parameters were measured for a period of 13 months under natural climatic conditions. The cumulative rainfall depth was about 2950 mm over the entire monitoring period. During rainfall, the presence of grass led to lower pore-water pressure (or higher suction) and volumetric water content in the three-layer landfill cover system. At the end of monitoring, the cumulative percolation was about 27 and 20 mm for the bare and grass-covered landfill covers, respectively. It is evident that the vegetated three-layer landfill cover system using recycled concrete without geomembrane can be effective in minimizing percolation in humid climates.
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