104 In conventional surface TSFs, both ℎand increase continuously throughout the life of the facility. In contrast, In-Pit TSFs maintain significantly lower values of ℎ, as tailings are deposited within a negative relief geometry. This fundamental geometric difference results in a substantial reduction in stored energy and, consequently, in the destructive potential of any hypothetical failure scenario (Davies & Martin, 2009). 4.4 Hydraulic Containment and Water Balance Control Hydraulic containment is the dominant design and operational control mechanism in In-Pit TSFs. The objective is to maintain inward-directed hydraulic gradients that prevent uncontrolled seepage from the facility into surrounding groundwater systems. The steady-state groundwater flow regime can be described using Darcy’s Law: =− ℎ (2) where: = seepage flow rate = hydraulic conductivity = cross-sectional flow area ℎ = hydraulic gradient By maintaining internal pond levels below surrounding groundwater heads, In-Pit TSFs promote inward seepage, effectively transforming the pit into a hydraulic sink. This condition enhances environmental protection and reduces the likelihood of contaminant migration (Younger et al., 2002). Water balance control, therefore, becomes a critical operational requirement, integrating inflows (precipitation, tailings water) and outflows (pumping, evaporation, seepage recovery). 4.5 Geomechanical Stability of Pit Slopes Under Tailings Loading The long-term stability of pit slopes is a key technical consideration in In-Pit TSF design. Unlike surface TSFs, where dam stability governs system performance, In-Pit TSFs rely on the inherent strength and confinement provided by the surrounding rock mass. Slope stability can be assessed using limit equilibrium or numerical methods, with the factor of safety (FoS) defined as: = Resisting Forces Driving Forces (3)
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