1017 industrial processing. According to Patterson et al. (2016), the performance and success of filtered tailings stacks depend on site-specific conditions, the scale of operations, and the geotechnical and geochemical characteristics of the tailings. Numerical modeling of infiltration using principles of unsaturated soil mechanics provides a valuable tool for evaluating recharge processes and optimizing drainage design (Watson, Sardana, & Sander, 1995). This approach allows for improved estimation of moisture conditions within tailings stacks. Nevertheless, uncertainties remain, particularly in the unsaturated properties such as the soil-water characteristic curve (SWCC) and permeability, which can significantly influence modeling results. This study aims to provide guidelines for the seepage analysis in Filtered Tailings Deposits located in high-precipitation regions, with the objective of highlighting the importance of conducting analyses that consider the unsaturated behavior of the materials. 2.THEORETICAL FRAMEWORK 2.1 Filtered Tailings According to ICOLD 181 (2021), filtered tailings has been put in practice since 1970s. Nevertheless, filtering was not feasible for many operations due to filtering equipment and the operational cost. In the recent years, filtering of tailings has significantly increased due to the improvement in the efficiency of the focus on reduced water consumption and filtering equipment, along with the reduced risks of stability and potential environmental risks. The filtered tailings are typically deposited in the storage facility and spread to minimize moisture loss until the optimum moisture content is reached. Subsequently, these materials are compacted to increase their strength and form a structural zone that allows them to support themselves (Sanchez & Parra, 2024). Typically, filtered tailings require dewatering to reach a solids concentration of 85% to 88% to achieve optimum moisture content and facilitate compaction. Generally, filtered tailings form a structural (compacted) zone and uncompacted tailings, as shown in Figure 71. The uncompacted zone may have a lower solids content and can be in the interior. Furthermore, this facility must have a seepage and runoff system collected in external collection ponds. Figure 71 - Schematic of a filtered tailings facility (ICOLD 181) 2.2 Unsaturated Soil Mechanics Unsaturated soils are typically described as systems composed of three phases: solid particles, pore water, and pore air. However, a more accurate representation includes a fourth phase, known as the air–water interface or contractile skin (Fredlund and Morgenstern, 1977). Compaction is a mechanical process aimed at increasing soil density by expelling air from its pore spaces. This technique is extensively applied in geotechnical engineering for the construction of infrastructure such as roads, dams, landfills, airfields, foundations, hydraulic barriers, and for ground improvement purposes. Laboratory compaction curves obtained from standardized tests are commonly used to guide field compaction control. The primary goal of these tests is to identify the optimum moisture content that will produce the maximum dry density, as well as to evaluate how soil properties change as the water content varies from optimum conditions (Fredlund & Rahardjo, 1993). Soil suction can be quantified based on the relative humidity at the water surface and is referred to as total suction. This suction consists primarily of two components: matric suction and osmotic suction. In addition, a component associated with adsorptive forces between water and solid surfaces has been identified (Yong & Warkentin, 1966), although this adsorptive suction is difficult to isolate and measure. Most geotechnical engineering problems can be effectively addressed by considering matric and osmotic suction,
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