Slope instabilities in Polish open-pit mines
Slope instabilities in two the largest Polish open-pit mines were registered every year. The Belchatow Opencast Mine located in central part of Poland is one of the largest in Europe. It is 12.5 km long, 3 km width and depth of 310 m. The total lignite resources of approximately 2 billion tonnes are divided into two exploitive fields Belchatow and Szczercow. The annual coal production of Belchatow Mine is 42 million tons. Another large mine, Turow Opencast Mine, is located in the southwest part of Poland in Lower Silesia District, close to German and Czech border. Estimated reserves of this coal mine are equal to 760 million tonnes and the annual production is 27.7 million tones. Due to the high depth of the mining operations and soil parameters in the mine smaller or larger sizes landslides have negative impact on coal exploitation and environment. Their volume ranged from few thousands to 3.5 Mm3. Most of the landslides were activated on structural surfaces and formed on south slope of the mine near deep secondary rift structure with the higher thickness of lignite deposit. Also Turow mine is threatened by landslide hazards. There were accidents in this area causing damages for mine infrastructure. In the past the potential hazard of development of the landsliding, breaking through the NysaLuzycka river, localized not far away from the mine, could resulted in trans-border environmental risks, flooding and destruction of mine infrastructure. However, this serious threat was eliminated by ground buttresses supporting the risk area. One of the largest landslides of 9 Mm3 occurred in on previous external embankments of Turow mine overlayers, close to the border with Czech Republic. Large and deep opencast mines are causing numerous slope stability problems. The largest landslides in Belchatow Mine were up to a few Mm3 and there were displacements of 2mm-2m per day. The author of this paper had in previous years opportunity to investigate one of the landslides. The research included CPTU in-situ tests, laboratory and modelling. This landslide occurred on the south slope of Belchatow mine. The interpretation of soil parameters was complicated due to partial saturation and preconsolidation of clayey soil. Full elimination of geo-hazards in these type of mines is not possible. Therefore special attention should be paid to compre-hensive site investigation, monitoring and numerical modelling for safe design of the exploitation processes. In the paper examples of slope instabilities that occurred in Polish open-pit mines and its external embank-ments of overlayers are presented. It is planned that new EU SLOPES project conducted by international consortium will help to implement new monitoring and research methods. Project will be conducted in one of the Polish, Czech and Spanish opencast mines. The obtained results should help in warning and mitigation of natural hazards. Although the mines has identified landslide triggers and remediation procedures, the full elimination of landslide hazards in open-pit mines of this size and deep is not possible.