103 particularly those relying on large embankment dams, concentrate vast volumes of tailings and water behind elevated artificial structures. This configuration results in high stored potential energy and a permanent reliance on active controls to maintain stability (ICOLD, 2011; Davies, 2002). Recent high-consequence failures have demonstrated that incremental improvements to traditional surface TSF designs are insufficient to effectively address their inherent risk profile. In many cases, the dominant risk drivers—such as dam height, stored water volume, and long-term dependence on human and mechanical systems—remain fundamentally unchanged (Morgenstern et al., 2016). In this context, risk is not only a function of failure probability but also of consequence severity, which is strongly influenced by facility geometry, containment philosophy, and water management approach. 4.2 In-Pit Tailings Storage Facilities as a Paradigm Shift The use of exhausted open pits as In-Pit Tailings Storage Facilities (In-Pit TSFs) represents a fundamental shift in tailings management philosophy. Rather than constructing new elevated containment structures, In-Pit TSFs utilize an existing excavation confined by competent rock masses, effectively reversing the energy profile of the storage system. In an In-Pit TSF, tailings are deposited below the surrounding natural ground level, significantly reducing gravitational driving forces and eliminating the need for large external dams. Containment is governed primarily by: • Hydraulic control through water balance and seepage management • Long-term geomechanical stability of the pit slopes • Progressive deposition and consolidation of tailings This configuration inherently lowers both failure probability and consequence severity, thereby enabling a structural reduction in catastrophic risk rather than relying solely on operational controls (Vick, 1990; Robertson, 2011). 4.3 Energy-Based Comparison Between Surface TSFs and In-Pit TSFs The potential energy stored within a tailings facility is a key indicator of its catastrophic failure potential. The total potential energy associated with stored tailings can be approximated as: =∫ ℎ (1) where: = tailings density = gravitational acceleration ℎ= vertical distance above the lowest release point = stored tailings volume
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