Verifying the Stability of the Working Fronts of Lignite Open Pits Developed in Hilly Areas—A Case Study of Jilț North Open Pit (Romania)

Abstract

Regardless of the period for which the lignite open pits from Romania will be kept in function, operational safety is an objective of utmost importance. In this context, the present paper aims to analyze the stability of the working fronts of a lignite open pit from Romania (Jilț North open pit). The development of Jilț North open pit involves excavations in a hilly area, with a level difference between the base of the open pit and the top of the hill of approx. 195 m (151 m by the end of 2023). Thus, based on the technical documentation provided by the mining operator (situation plan, cross-sections, stratigraphic columns, etc.) and laboratory tests (on the physical–mechanical characteristics of the rocks), a stability analysis model was created with the help of a specialized software. Following the analyses, it was found that two of these slopes (T1 and T3 steps) do not present a sufficient stability reserve (in fact they are unstable, Fs ˂ 1), to allow continuing extractive activities under safe conditions. Considering these results and using a well-known slope dimensioning method, two technical solutions were proposed to increase the stability reserve: a simple one, for the T3 step, which involves reducing the slope angle from 52° to 45°, and the second one, for the T1 step, a bit more complex, involving the inclusion in the general continuous flux of the open pit of a discontinuous sub-flux that aims to achieve three sub-steps, and the reduction in the general slope angle.

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

“…Geologically, the deposits in Oltenia belong to the Pliocene formations (Dacian and Romanian) and are made up of 21 layers of lignite, with variable extents, separated by sterile rocks (soft, cohesive and non-cohesive rocks, predominantly clays and sandy rocks) [2,39,40].…”

“…The thickness of the lignite layers varies from a few centimeters to several meters, appearing in a compact form or in the form of several coal banks, which make up the complex of a layer [2]. Being the most extensive sub-basin in Oltenia, it is also characterized by the most complex tectonics.…”

“…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].…”