Stability Conditions in Lignite Open Pits from Romania, Case Study: Oltețu Open Pit

Abstract

The problem of the slope stability of open pit mines is one of constant interest and great importance, both during the period of operation, but also post-closure. The research focused on the Oltețu open pit (located in Berbesti Mining Basin, Romania) and was directed in such a way as to allow consideration in the stability analyses of natural (predisposing the investigated area to landslides) and anthropogenic (specific to open pit mining) factors and causes as well as their combined effect. The field investigations (observations on the technical condition of the slopes, discussions with the technical personnel from Oltețu open pit, and sampling) were completed with analyses and laboratory tests (physical–mechanical properties of rocks in the composition of the slopes). The stability analyses took into account different hypotheses related to the actual geometry of the working slopes, and a predictive analysis was also carried out for the forecasted evolution of the working fronts and lateral slopes. Following stability analyses, it was found that for most slopes, the stability reserve is insufficient to allow continuing lignite exploitation under safe conditions. The last part of the paper presents the solutions identified by the authors (adoption of new geometries of the working front and lateral slopes) in order to increase the stability reserve to a minimum acceptable level, which would allow the safe continuation of lignite extraction, and, in the end, some practical recommendations are briefly presented.

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

“…Functioning as a sedimentation basin, the deposits in the region are mainly made up of sandstones, conglomerates, sands and gravels, which host the lignite layers. The foundation of the Getic Depression consists of crystalline schists with granitic inclusions and a cover of Mesozoic sedimentary formations [1,39,40].…”

“…In order to highlight the influence that seismic movements in the Oltenia mining region can have on the stability of the mining works in the three studied perimeters, we considered several previous studies, conducted by the authors and their collaborators [1,2,38,41,[59][60][61].…”

“…Slope failure in any open pit may lead to serious consequences. Among the more serious consequences are damage or destruction of machinery (bucket wheel excavators-BWEs and spreaders), negative effects on nearby ecosystems, the destruction of road and railway infrastructure or even the death of operating staff or people living in neighboring areas [1,2].…”

“…For the sustainable development of lignite mining, whenever unexpected sliding phenomena occur their causes must be identified, and appropriate measures must be taken in order to eliminate their effects [1,2,[11][12][13][14][15][16]. Monitoring stability conditions and the development of early warning systems are the main ways to prevent slope failure that may result in material and/or human loses [1,[17][18][19][20][21][22][23][24].…”

The influence of loose layer water cut-off curtain on the slope stability of open-pit coal mines

“…The mechanical parameters of rock are obtained by a laboratory test, and the stability of the high slope is quantitatively analyzed by two-dimensional limit equilibrium and three-dimensional numerical simulation(SU 2022). The research focused on the Oltetu open-pit and was directed in such a way as to allow consideration in the stability analyses of natural (predisposing the investigated area to landslides) and anthropogenic (speci c to open-pit mining) factors and causes as well as their combined effect (Lazar 2022). The large-scale numerical model was built, based on the site observations, large scale LiDAR data, in situ characterisation tests, and statistical analysis of geotechnical data, on DTMs de ning the complex geology of the site and local and global safety factor were calculated using the strength reduction method (Renaud 2022).…”