107 5.3 Integrated Geotechnical and Hydrogeological Analysis Detailed engineering assessment includes coupled geotechnical and hydrogeological analyses to evaluate long-term stability and containment performance. Geotechnical analyses focus on: • Pit wall stability under progressive tailings loading • Stress redistribution within the rock mass • Potential for time-dependent deformation Hydrogeological analyses assess: • Groundwater–tailings interaction • Seepage direction and hydraulic gradients • Long-term pore pressure evolution Numerical models are developed to simulate progressive pit filling, accounting for staged deposition and water management strategies. These analyses support verification of inward seepage conditions and stable groundwater regimes (Younger et al., 2002; Vick, 1990). 5.4 Risk-Informed Engineering Decision-Making Engineering decisions for In-Pit TSFs are guided by a consequence–probability framework consistent with international tailings risk management practices (Morgenstern et al., 2016). Overall risk is defined as: = × (7) Where: • = probability of failure • = consequence of failure In-Pit TSFs inherently reduce due to their negative relief geometry and confinement within competent rock mass, while controlled deposition and water management reduce . 5.5 Multi-Criteria Decision Analysis (MCDA) Final selection of an In-Pit TSF alternative is supported by a Multi-Criteria Decision Analysis (MCDA) incorporating technical, environmental, social, and economic factors. A decision index is calculated as: =∑ =1 ⋅ (8)
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