Contradictive mining–induced geocatastrophic events at open pit coal mines: the case of Amintaio coal mine, West Macedonia, Greece

Abstract

For open pit coal mines, subsidence of the surrounding area and landslides are among the most common mining-induced catastrophic geohazards. These large-scale geohazards are related to both hydrogeological and geotechnical parameters, and they cause substantial damage. A major challenge to managing these hazards is that the factors that trigger these two phenomena are diametrically opposed. Land subsidence is triggered by the overexploitation of the aquifers conducted for the protection of the slope’s stability. Thus, the reduction of groundwater pumping from the draining wells reduces land subsidence deformations but at the same time decreases the stability of the slopes. In the present study, the investigated site is the area at the perimeter of the Amyntaio opencast coal mine at Florina Prefecture, Northern Greece. The overexploitation of the aquifers for the dewatering of the slopes turned the mine into a large-diameter well. The land subsidence caused by the dewatering extended 1–3 km around the mine, affecting the villages of Anargiroi and Valtonera. Furthermore, on June 10, 2017, a massive landslide of approximately 80 million cubic meters occurred at the working slopes of the mine, burying 25 million tons of lignite, resulting in severe damage to a large amount of mining equipment and causing the evacuation of the nearby Anargyroi village. The geometry of the slopes, the preexisting sheared zones, the extensive faults intersecting the site, and the high piezometric loads underneath the floor of the open pit as well as the high groundwater level of the shallow aquifers are the main causal factors of the landslide. The current research, besides presenting the two catastrophic events, aims to correlate the geological, hydrogeological, and geotechnical factors affecting both phenomena, outlining their opposing mechanisms. The study proves the necessity of the establishment of a holistic development plan supported by focused geotechnical and hydrogeological studies. This way, the occurrence and the diametric drivers of both types of catastrophic events can be evaluated and predicted, minimizing their effects on the mining activities and the surrounding environment.