90 2.3. Soil-Water Characteristic Curve (SWCC) The Soil-Water Characteristic Curve (SWCC) offers a conceptual framework that relates the mass and/or volume of water in a soil to the energy state of the water phase. It has been widely used as an interpretive model based on fundamental capillary concepts to explain how water is distributed within soil voids. Additionally, factors such as soil plasticity, particle size distribution, and void ratio are commonly incorporated into the interpretation of laboratorymeasured SWCC data. When using a soil-water characteristic curve (SWCC) to calculate soil suction, it is essential to know the curve’s parameters. SWCCs typically have a sigmoidal shape, which can be described using three fitting parameters, commonly labeled “a”, “n”, and “m”. The “a” parameter usually represents a suction value slightly higher than the soil’s air-entry value (AEV). The “n” parameter indicates how quickly the soil desaturates once suction surpasses the air-entry point. In some models, “m” parameter is included to provide additional flexibility in fitting the SWCC data. Additionally, the saturated gravimetric water content ( ) must also be determined (Fredlund et al., 2012). In this study, the Fredlund & Xing model (1994) was used to analyze the behavior of filtered tailings under unsaturated flow conditions. This model allows the soil-water characteristic curve (SWCC) to be described by fitting parameters that define how volumetric water content varies with suction in porous materials. The Fredlund & Xing model can be represented mathematically as: ( ) = ( ) ( ( +( ) )) Where is the suction (kPa), ( ) is the volumetric water content at suction, is the saturated volumetric water content, is the natural number (2.71828), , , are model fitting parameters and is a correction coefficient that allows a progressive decrease in water content at high suction forcing the function through a water content of zero at one million kPa.
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