97 In contrast, the only saturated model, a more pronounced piezometric level is observed within the FTD. Since this model does not account for changes in permeability or degree of saturation as a function of suction (negative pore water pressure), it assumes that the material below the piezometric level is 100% saturated, whereas the material above it is considered “dry.” Figure 9 – Piezometric line and Pore Water Pressure in the Only Saturated Model 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. 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 saturatedunsaturated 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 Saturated Dry
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