Stability and characterisation of spoil heaps in European surface lignite mines: a state-of-the-art review in light of new data

The large amount of spoil material produced during the mining process imposes a significant economic and environmental liability on lignite producers. In this context, the present paper provides an overview of the geotechnical characteristics of European lignite mine spoil heaps and discusses their significance to the stability of the heaps. In order to achieve this, samples collected from spoil heaps of Polish, Czech and Greek mines are analysed and the results are compiled with data from the literature. A major conclusion drawn is that both physical and engineering properties of spoil heaps indicate a noteworthy variability, which is larger than typical in-situ ground material. This is because of the additional factors affecting spoil heap deposition, such as the transportation and dumping method. Furthermore, failure mechanisms and case histories of large instabilities in lignite spoil heaps are critically discussed in order to better understand triggering failure mechanisms. It is concluded that classical assumptions made for natural soil slopes and relevant limit equilibrium models should be cautiously applied to spoil heaps. The challenges associated with numerical and probabilistic modelling of spoil heap stability, such as the inherent spatial variability of spoils and the time-dependent changes in their geotechnical properties, are also critically discussed. Finally, important research gaps in design and analysis of spoil heap stability, such as the absence of appropriate constitutive models developed specifically for spoil materials, are summarised

Geotechnical Characterization of Fine-Grained Spoil Material from Surface Coal Mines

Coal mines produce large amounts of excavated waste soils, known as spoils. These materials can cover vast areas, are typically dumped in heaps without any treatment and are difficult to exploit for engineering purposes because of their significant variability. Efficient exploitation of spoil heaps poses engineering challenges, related mainly to the involved degree of uncertainty. A small number of studies have attempted to characterize the geotechnical properties of spoil material; however, there remains a considerable gap in understanding how to deal with spoil materials in the context of sustainable development and civil infrastructure design. In this work, a systematic effort is made to quantify the uncertainty of the geotechnical properties of a particular spoil heap. Laboratory test results based on an extended investigation of a spoil material originating from lignite coal mines are gathered in one database and thoroughly analyzed. The results reveal and quantify the significant spoil material variability, which is contrasted against data for common soils, while a systematic approach is proposed for spoil material characterization

Slope failure incidents and other stability concerns in surface lignite mines in Greece

An important aspect of the Greek surface lignite mines relates to the stability of the corresponding excavations. The more recent ones, over the last few decades, have become larger and deeper (up to 200m) compared to those in the past and, as a result, more difficult to manage. In fact, during the last ten years, several incidents of excessive deformations or catastrophic slope failures have been reported. Therefore, a robust practice of geotechnical engineering is very important. The scope of the present work is to provide a critical review of the relative literature on slope failure incidents and other stability concerns, and also to briefly present cases for which no information has been published in the past. The paper consists of three sections: an inclusive review of early studies, a more extensive review of recent cases of stability problems, and a critical discussion on commonly anticipated failure mechanisms. Based on the above, relevant conclusions are drawn and discussed. Overall, it is concluded that thorough practice of geotechnics is becoming increasingly crucial for the effective and sustainable management of the Greek lignite mines