1022 Figure 76 – Net precipitation During the dry season, net precipitation values are lower than zero. Conservatively, a net precipitation of zero liters/month/m² has been assumed for these months. These values will vary depending on the sector where they are applied as boundary conditions. In the case of the structural zone, since it is covered during the wet season, net precipitation is considered to be zero. In contrast, in the drying areas, net precipitation values are influenced by tailings infiltration with a higher moisture content. The average infiltration considered to simulate the additional infiltration of tailings originating from the plant was 42.31 liters/month/m². Surface water was represented by a boundary condition with a hydraulic head of 1.00 m at the rear of the deposit, simulating flows that could continuously enter the collection system. This condition is conservative, considering that the collection system will not allow the accumulation of flows in that sector. 3.3 Numerical Modelling The geometry used for the seepage analysis corresponds to the most representative section crossing the FTD. Four materials constitute the interior of the FTD: (1) filtered tailings, (2) collection system, (3) starter dam, and (4) impermeabilization system. For modeling purposes, the collection system was simplified by including a drainage material layer at the bottom of the deposit, which will convey FTD flows toward its base. In addition, two starter platforms were considered to allow the initiation of horizontal tailings stacking. The impermeabilization system, which will be installed at the bottom of the deposit to prevent infiltration of FTD flows, was conceptualized by the numerical model boundary, which acts as an ideal barrier. As part of the construction procedure, the filling curve shown in Table 19 was considered. A total of four boundary conditions were implemented in the FTD infiltration analysis: (1) net precipitation, (2) drying area, (3) drainage, and (4) runoff water. The analysis conditions considered are as follows: • Wet season: During the wet season, from December to March, tailings are accumulated in the Filtered Tailings Temporary Storage Area. During this period, the face and the structural zone (corresponding to the first meters of the upper platform of the initial engineering stage) must be covered. Subsequently, during construction stage (stacking), the structural zone must remain covered. • Dry season: From April to November, tailings stacking will be carried out, with the material compacted to 98% of the MDD according to the Standard Proctor test. • Runoff: Runoff water will be conveyed toward the rear of the FTD with a maximum slope of 2%, entering the collection system and being routed to the collection pond through the bottom of the deposit. • Type of analysis: A two-dimensional (2D) transient analysis was performed, considering an analysis period of 5,475 days, equivalent to approximately 15 years. • Pore pressure activation: The pore pressure activation value for the tailings material corresponds to the upper moisture limit (15%), thus simulating the most unfavorable condition under which compacted tailings may be placed. 0.E+00 5.E-09 1.E-08 2.E-08 2.E-08 3.E-08 3.E-08 4.E-08 4.E-08 0 60 120 180 240 300 360 Infiltration of drying area (lt/mes/m²) Time (days)
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