Geotechnical Guidelines for Open Pit Closure – a new publication by the Large Open Pit (LOP) project

Graaf, Phil de; Beale, Geoff; Carter, Trevor; Dixon, J.D.

doi:10.36487/acg_repo/2152_120

Cited by 4 publications

(1 citation statement)

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“…However, as outlined by de Graaf et al (2019), up until now, no generalised industryaccepted guidance for mine slope stability closure DACs exists. The proposed Large Open Pit (LOP) Project Mine Closure Guidelines are now attempting to address this ( de Graaf et al 2021).…”

Section: Design Service Lifementioning

confidence: 99%

Transitioning from mine operations to closure: the dilemma of differing geotechnical design acceptance criteria perspectives

Carter¹,

Graaf²,

Dixon³

et al. 2022

Mine Closure 2022: 15th Conference on Mine Closure

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For open pit mining, understanding and managing slope performance is critical for both operations and closure. Towards the end of mine life, achieving reliability of slope performance in operations often necessitates real-time implementation of active slope stabilisation controls. This situation changes significantly towards closure, when production economics are no longer the priority, and resources for field monitoring control and active slope management diminish. The risk profile also shifts to a greater focus on stakeholder needs, including the environment and social acceptance, as land use changes. Although risk profiles will shift, the safety goal of 'zero harm' needs to continue to be achieved through all phases.Historically, most final pit slopes were not designed for closure. Rather, they tended to be optimised for production efficiency and thus were typically too steep for long-term reliability. The key question then becomes -what happens when the controls that have been put in place for maintaining their stability are decommissioned for closure? With sufficient understanding gained during operations, it may be possible to adequately forecast behaviour and define a Design Acceptance Criteria appropriate for the slope, for post-closure, once operational controls are decommissioned. This paper is hoped will help address this dichotomy and provides suggestions to meet industry objectives. It is also intended to promote discussion on this transition, such that industry and regulator perspectives can be accommodated alongside each other within the forthcoming Large Open Pit (LOP) Guidelines for Mine Closure handbook publication, currently in preparation under the auspices of the LOP initiative.

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Section: Design Service Lifementioning

confidence: 99%

Transitioning from mine operations to closure: the dilemma of differing geotechnical design acceptance criteria perspectives

Carter¹,

Graaf²,

Dixon³

et al. 2022

Mine Closure 2022: 15th Conference on Mine Closure

Self Cite

View full text Add to dashboard Cite

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The role of pit lake thermal dynamics on the thermal performance of ground heat exchangers

Carcamo-Medel,

Narsilio,

Fuentes

2024

Sci Rep

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The addition of ground heat exchangers (GHEs) to a pit lake’s basin has the potential for abundant, clean and renewable geothermal energy extraction using shallow geothermal systems. Basin-embedded GHEs avoid direct interaction with mine water, which has been shown to impact efficiency and longevity in mine open-loop geothermal systems negatively. The now accelerated closure of open-pit coal mines presents itself as an opportunity to use this technology. However, no guidelines currently exist for designing or operating GHEs embedded in the sediment of water bodies. Furthermore, the two-way coupling between the complex annual thermal fluid dynamics that lakes are naturally subjected to and heat fluxes on the sediments and the GHE system has not been explored. In this study, we develop and validate finite element models to assess the relevance of lake thermal stratification in the performance of a geothermal system embedded in water bodies basins, e.g., on open-pit mine closures, under temperate residential thermal loads. The results show that the pit lake’s role as a thermal sink improves significantly when the lake’s thermal dynamics are accounted for, with an increase of up to 292% in the lake’s available energy budget. A minor variation in energy budget (~8%) was found whether the lake is modelled explicitly or simplified as a transient Dirichlet temperature boundary condition. This small difference vanishes if horizontal circulation along the lake is considered, highlighting the lake’s thermal energy potential. Finally, the impact on the GHE Coefficient of Performance (COP) is evaluated, with a maximum of ~15% difference among all cases.

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Geotechnical Issues in Decommissioning Surface Lignite Mines—The Case of Amyntaion Mine in Greece

Kavvadas

Roumpos

Servou

et al. 2022

Mining

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Recent changes in the fossil-fuel energy sector require coal mining industries to plan for the future, including developing procedures for decommissioning and closure associated with mines. In surface coal mining, the geotechnical issues of decommissioning include the long-term stability of the pit slopes, particularly as the pit is gradually filled with water. This paper investigates such slope stability issues, with emphasis on the conditions prevailing in the Amyntaion surface lignite mine, in Western Macedonia, Greece. Analytical and numerical methods have been developed and used to estimate the temporal evolution of the overall safety factor, as the water level in the pit rises, creating a lake. It is shown that until the water level in the lake reaches a critical depth of approximately 15–35% of the final equilibrium condition, the safety factor against the overall slope instability decreases slightly (by about 3% in the case study, and up to 5–10% in other conditions) compared to its value at the end of exploitation. At higher lake levels, the safety factor increases significantly, as the beneficial effect of the lake water pressure acting on the slope overcomes the adverse effect of pore water pressure rise inside the slope. In typical mines, the critical water depth is achieved within a few years, since the surface area of the pit is smaller at deeper levels; thus, more favorable slope stability conditions are usually reinstated a few years after mine closure, while the small reduction in safety during the initial stages after closure is inconsequential. The paper investigates the parameters influencing the magnitude of the small reduction in the short-term safety factor and produces normalized graphs of the evolution of the safety factor as the lake water level rises. The results of the analyses can be used in preliminary closure studies of surface coal mines.

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Geotechnical Guidelines for Open Pit Closure – a new publication by the Large Open Pit (LOP) project

Cited by 4 publications

References 0 publications

Transitioning from mine operations to closure: the dilemma of differing geotechnical design acceptance criteria perspectives

Transitioning from mine operations to closure: the dilemma of differing geotechnical design acceptance criteria perspectives

The role of pit lake thermal dynamics on the thermal performance of ground heat exchangers

Geotechnical Issues in Decommissioning Surface Lignite Mines—The Case of Amyntaion Mine in Greece

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