A very complex failure took place at an open-pit coal mine in the eastern Turkey. The floor of the open-pit heaved up as a result of the buckling failure of the coal seam and a combined form of shear and sliding failure of slope benches occurcd. The investigations showed that a weak clay band within the coal seam was the main cause of the failure. The friction angle of this band was less than 3° and dipped into the pit with an angle of 5-7°. The failure took place while the coal seam was uncovered. In this paper, the causes of the failure are investigated through some back analyses of failure modes on the basis of geotechnical investigations, limiting equilibrium techniques and finite element analyses and the outcomes of these studies are presented and discussed. © 1996 Balkema, Rotterdam.