Reassessment of the Stability Conditions in the Lignite Open Pits of Oltenia (Romania) in Relation to the New Local Seismic Context as an Imperative for Sustainable Mining

Responsible mining considers the three pillars of sustainability, namely the environment, the economy and social welfare. As a result, exploitation of deposits of useful mineral substances, as an economic activity, must be carried out taking into account several requirements, among which is the generation of a reduced impact on the environment and local communities. Sliding of open pits and waste dumps slopes represents a major risk, which endangers workers and machinery, as well as the components of the natural and built environment in the influenced area. In order to avoid such phenomena and their consequences, it is imperative to analyze the stability conditions whenever their possible triggering factors appear (such as earthquakes). Between February and March of 2023, the region of Oltenia (south-west Romania) was affected by intense seismic activity, out of normal patterns. Considering this series of seismic events, in this paper we aimed at reevaluating the stability conditions of the slopes of the working fronts and of the internal dumps in the lignite open pits located in the region in this new context. Research focused on three lignite open pits, namely Peșteana North (Rovinari mining perimeter), Jilț North (Jilț mining perimeter), Berbești–Alunu (Berbești mining perimeter). After describing the general geology and tectonics of the areas under study, the seismic episode that affected the region at the beginning of 2023 (which in fact extended until November) is highlighted, with increased attention given to the earthquakes of 13 and 14 February 2023, with a local magnitude ML ≥ 5. The most important part of the study is represented by the stability analyses, carried out for normal conditions (considering the characteristics of the rocks at natural humidity and in the absence of the influence of external factors) and under seismic conditions, characterized by a peak ground acceleration equal to the maximum acceleration considered for the location area of the mining perimeters taken into study. The results of the study showed that, for most of the analyzed situations, a renewal of the technical exploitation documentation is required, which, taking into account the results of this study, must adopt new geometries of the excavation and deposition fronts, so that the objectives in terms of operational and workplace safety imposed by legislation are respected.