## 1 Introduction  
Twenty years ago, twenty open pits (of different sizes) were in operation in the mining area of Oltenia (in the five mining basins: Rovinari, Motru, Jilt, Mehedinti and Berbesti); currently, only ten are functional, some of which are soon to be closed (by depleting reserves, due to lack of financial viability, or as a result of policies to eliminate fossil fuels from the national energy mix). Precisely because of the decarbonization policies of the energy sector in the EU and, implicitly, in Romania, all these open pits are to be closed in the next 10-12 years (in the absence of reassessments of the current ambitions and targets set at the EU level). Although the share it has in the national energy mix of Romania has decreased from over 30% (10 years ago) to approx. 15%, lignite continues to play an important role, and this situation is expected to be maintained for the next few years. After this period, the fate of lignite, and implicitly of lignite open pits, is an uncertain one, if we consider, on the one hand, the obligations to eliminate fossil fuels from the energy sector assumed by Romania through the European Green Deal and the National Resilience and Recovery Plan, in accordance with the European decarbonization ambitions and policies, and on the other hand, the conflict taking place in Ukraine and its implications for the energy market. Even under these conditions, operational safety is an aspect that cannot be overlooked, neither during the period in which extractive activities will continue, nor during the closure and post-closure phase of these mining perimeters. Slope stability is one of the most important issues which must be solved throughout the lifetime of any open pit or quarry. In the particular case of lignite open pits, which usually operate in soft rocks, there is a high probability for slope sliding to occur [1]. The failure and sliding of slopes in an open pit can be triggered by multiple factors, among which are poorly designed geometric elements, insufficient knowledge of the geology and hydrogeology of the lignite deposit, the presence of uninvestigated failure plans (faults), external factors (overloads, seismic loads, precipitations), etc. [2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14]. Among the consequences of landslides produced over time in lignite open pits are the total or partial damage of machinery, mostly bucket wheel excavators (BWEs) [15; 16; 17], the degradation or destruction of the nearby habitats involved in the sliding process, the blocking of water courses, the destruction of communication routes, or even the death of people operating the machines or who live in nearby areas [1]. The partial or total destruction of BWEs (Figure 1) causes significant financial losses to mining operators, by interrupting the technological flux, by the penalties resulting from the inability to supply lignite to thermal power plants, but, above all, by the intrinsic value of these machines (depending on the age and degree of wear and tear from a few million euros up to approx. EUR 100 million for the largest and most modern of these, the Bagger 293 BWE). In general, although open pit operators have in mind different measures to avoid the occurrence of slope slides, these often prove insufficient, being practically impossible to consider all the variables involved in this process. In fact, slides that affect the slopes of lignite open pits, produced by the failure of the excavation step or the one on which the BWEs vehicles are working, are quite common phenomena, their occurrence and manifestation being signaled all over Europe (in Romania, Poland, Czech Republic, Greece, Serbia, Kosovo, Germany, and Spain), but also in other parts of the world (in USA, China, India, Brazil, etc.). These slope slides are well described in the literature, in terms of favoring/triggering factors and causes, unfolding mechanisms, damage caused, and preventative measures for the future [19; 20; 21; 22; 23; 24; 25; 26].