1027 IN-PIT TAILINGS STORAGE FACILITY (IN-PIT TSF): THE EXHAUSTED OPEN PIT AS A HIGH-PERFORMANCE SOLUTION FOR SAFE AND SUSTAINABLE TAILINGS MANAGEMENT IN MODERN MINING *K.J. Cáceres1, J.O. Gutierrez2 1Department of Hydraulic Engineering, Anddes Asociados Sac, National University From Cajamarca, Perú, (*Presenting author: caceresmendozakarol@gmail.com) 2Department of Civil Engineering, Gold Fields, Ricardo Palma University, Perú, (javier.gutierrez@goldfields.com) ABSTRACT Tailings management has emerged as one of the most critical technical, environmental, and social challenges facing modern mining. Conventional surface tailings storage facilities (TSFs), particularly those relying on large containment embankments, concentrate vast volumes of tailings and water behind elevated engineered structures, resulting in high levels of stored potential energy and a permanent dependence on active controls to maintain stability. Recent high-consequence failures have demonstrated that incremental improvements to traditional designs are insufficient to effectively address the inherent risk profile of this type of facility. In this context, the use of exhausted open pits as In-Pit Tailings Storage Facilities (In-Pit TSFs) represents a fundamental shift in tailings management philosophy. By utilizing an existing mining excavation confined by a competent rock mass, In-Pit TSFs eliminate the need for elevated embankment dams and shift system control toward hydraulic containment, long-term geomechanically stability, and riskbased operational management. This paper presents a comprehensive technical framework for the evaluation, design, and decision-making associated with In-Pit TSFs, integrating geotechnical, hydrogeological, and hydraulic analyses, as well as risk management principles aligned with international standards such as the Global Industry Standard on Tailings Management (GISTM). The analysis demonstrates that, when integrated early into life-of-mine planning, In-Pit TSFs enable a structural reduction of catastrophic risk and constitute a technically robust and sustainable alternative for tailings management in open-pit mining. KEYWORDS In-Pit TSF; tailings management; geotechnical stability; hydraulic containment; risk-based design, sustainable mining 1. CONTEXT AND PROBLEM STATEMENT The mining industry is facing increasing pressure to substantially improve the safety and sustainability of tailings management. At a global scale, surface tailings storage facilities have historically been designed using prescriptive approaches focused on static factors of safety and on the performance of embankments progressively constructed from materials with highly variable strength properties. While these approaches have enabled large-scale mining development, they have also resulted in systems that are highly dependent on active controls, permanent maintenance, and flawless operational performance over decades or even centuries (Vick, 1990). Recent tailings facility failures have shown that risk is not solely associated with operational errors or isolated extreme events, but is fundamentally linked to the intrinsic configuration of the system: large volumes of saturated tailings and water retained at elevation behind engineered structures whose failure releases substantial amounts of stored potential energy (Fourie & Blight, 2015). In response, the mining industry has strengthened regulatory frameworks and adopted global standards such as the GISTM. However, there is growing consensus that meaningful improvements in tailings safety require moving beyond incremental enhancements to traditional designs and toward solutions that reduce
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