Stability and movements of open-pit lignite mines in Northern Greece

This paper presents a case of a lignite mine in Northern Greece with excavated slopes exceeding 100-120m in depth in which substantial movement is occurring, with an average rate 10-20mm/day. The Mavropigi mine is very important for the power supply of Greece and uninterrupted operation is often critical, meaning that excavation is taking place on moving soil masses. The stability of the moving southeast slope is investigated and the information developed from an extensive monitoring campaign, with survey prisms, inclinometers and piezometers is presented. The use of the investigation data to evaluate the type of movement, the geometry of sliding surface and the effectiveness of remediation measures are analyzed in detail. The procedure of assessing the stability and safe slope operation during production, even with high rates of movement and the effect of precipitation are presented. It is shown that there are situations that mine slopes can move several meters laterally and still be operational without catastrophic failures.