1025 In addition, positive pore water pressures are generated within the FTD, taking the piezometric line (u = 0 kPa) as the reference level. The model assumes that no negative pore water pressures (suctions) develop in the remainder of the domain. Therefore, since permeability and volumetric water content are considered constant, no changes occur in these properties or in the degree of saturation. This approach is commonly adopted when unsaturated behavior is not considered in engineering projects; however, this assumption may be unrealistic, as an unsaturated soil exhibits a residual volumetric water content even above the piezometric surface. 5. CONCLUSIONS The seepage analysis results indicate that a piezometric level develops within the FTD throughout both the operational life and the construction stage of the dam under both modeling approaches. However, incorporating unsaturated behavior through the soil–water characteristic curve (SWCC) enables a more realistic representation of pore water pressure distribution, degree of saturation, and permeability variation as a function of suction. The saturated-unsaturated model captures the gradual transition between saturated and unsaturated zones, as well as the development of significant suction values (on the order of -2200 kPa), which directly influence the hydraulic response and potentially the stability of the deposit. On the other hand, the only saturated model simplifies the hydraulic behavior by assuming constant material properties and neglecting negative pore water pressures. This results in a more sharply defined piezometric surface and an abrupt separation between “saturated” and “dry” material, which may not accurately represent actual field conditions, particularly in filtered tailings deposits where unsaturated behavior is relevant. From an engineering perspective, the use of a saturated model may lead to conservative or, in some cases, non-representative estimates of moisture content and pore pressure distributions, whereas an unsaturated model allows for a more accurate assessment of permeability changes, storage capacity, and strength contributions associated with suction, with significant implications for stability analyses, deformation predictions, seepage control, and the design of construction measures such as surface covering during the wet season. Additionally, it should be emphasized that certain zones within the filtered tailings deposit exhibit high degrees of saturation (greater than 85%); under seismic loading, these highly saturated areas may become susceptible to liquefaction, potentially reducing shear strength toward residual values and triggering a residual response in the tailings, which could ultimately lead to instability or failure. REFERENCES Aitchison, G. (1964). Engineering concepts of moisture equilibria and moisture changes in soils. Statement of the Review Panel, In Moisture Equilibria and Moisture Changes in Soils Beneath Covered Areas. A Symposium in Print , 7-21. Copeland, A., Daigle, V., & Strauss, A. (2023). Is the implementation of dry stacking for tailings storage increasing? A Southern African perspective . Paste 2023, 611-619. Davies, M. (2011). Filtered dry stacked tailings: the fundamentals. Proceedings of Tailings and Mine Waste 2011. Fredlund, D., & Rahardjo, H. (1993). Soil Mechanics for Unsaturated Soils. New York.: John Wiley & Sons Inc. Fredlund, D., & Xing, A. (1994). Equations for the soil-water characteristic curve. Canadian Geotechnical Journal, 521-532. Fredlund, D., Rahardjo, H., & Fredlund, M. (2012). Unsaturated Soil in Engineering Practice. New Jersey: John Wiley & Sons. Garcia, L., Lemos, M., & Gomes, G. (2024). Compaction Sensitivity in Tailings Stack Infiltration Modeling: Unsaturated Properties Uncertainty Analysis. Tailings and Mine Waste 2024. Genuchten, V. (1980). A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Science Society of America Journal 44, 892–898. ICOLD. (2021). Bulletin 181: Tailings Dam Design - Technology Update. Patterson, K., McLeod, H., Hegaroden, D., Parkinson, G., Williams, P., & Murphy, B. (2016). Are filter tailings practical for a high production mine in a cold, wet climate? Proceedings of the 20th International Conference on Tailings and Mine Waste, 359–371. Sanchez, E., & Parra, D. (2024). Proceedings of Tailings and Mine Waste 2024 . Performance assessment of a filtered tailings storage facility partially built with uncompacted tailings .
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