FEM and LEM stability analyses of the fatal landslides at Collolar open-cast lignite mine in Elbistan, Turkey

On February 2011, two landslides took place in Collolar the lignite mine within 1week. The first landslide, which occurred at the permanent slopes located in the southwest of the pit, resulted in one fatality and temporary cessation of production activities. Four days later, a second landslide, larger than the first, occurred in the temporary production slopes (northeast of the same pit). The second landslide, with a volume of about 50Mm(3) soil, resulted in ten fatalities including geological and mining engineers. In the present study, a series of numerical analyses were carried out using the finite element method and the limit equilibrium method to evaluate factors that caused the landslides. Three different depths were considered for the level of ground water table. The safety factors in the permanent slopes were found to be around one or less even if the level of groundwater table was relatively low. It was concluded that the first landslide at the permanent slopes happened possibly due to the high level of water table which was continuously fed by the Hurman River. On the other hand, despite relatively higher safety factors, the failure of the production slopes was triggered probably due to instability introduced by the first landslide.