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.