ABSTRACT:

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 occurred. 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.

RESUME:

Une rupture tress complex est. serene dans une mine de carbon à ceil overt à lest de la Turquie. Le planchcr de la mine s'est souleve à la suite du flambage d'une veine de carbon. Les terrasses en pente se sont effondrees sous une forme combinee de cisaillement et de glissement. Les recherches ont indique que la cause principale de la rupture fut la presence d'une couche d'argile situee dans la veine du carbon. Cette couche ayant un angle de frottement inferieur à 3° etait inclinee de 5° à 7° vers la pente. La rupture s'est produit lors de I'excavation de cette couche.

ZUSAMMENFASSUNG:

In einer offenen Grube einer Kohlenminein der Osttuerkei fand ein komplizierter Bruch statt. Der Boden der offenen Grube hob sich auf Grund eines knicken eines kohlestreifens welcher mit einer Scherung und einer Abrutschung einer treppenartigen Böschung kombiniert war. Untersuchungen haben gezeigt, dass ein weiches Tonlage die Hauptursache des Bruches war. Der Reinbungswinkel dieser Lage betrug weniger als 3° und hatte einen Einfallswinkel von 5°-7°. Der Bruch ereignete sich wahreud der Ausgrabung del' Kohlendecke.

1 INTRODUCTlON

A very complex failure took place at the Kişlaköy open-pit mine of Afşin-Elbistan Lignite Mining Complex in the Eastern Turkey in 1984. The pit-floor heaved up as a result of the buckling failure of the lignite seam and a combined form of shear and sliding failure of mining benches occurred. The investigations showed that weak clay layers existed in the lignite seam of about. 20 m thick and one of these clay layers played an important role in the failure. The friction angle of this layer was about 3° and dipped into the pit with an angle of 6° (Ulusay et al. 1986). The main failure occurred on July 1, 1984 at the North-West slope of the kişlaköy open-pit. (Polat and Yueksel 1984). The failure involved a region, which was 650 m long and 250 wide (Fig. 1). The length of the region was later extended to 1000 m with subsequent failures. The final horizontal movement of the failed slope was more than 50 metres. The lignite seam of the pit-floor was heaved up and it had a set of buckles whose strikes were almost perpendicular to direction of movement and parallel to the axis of benches (Fig.2). Fig. 3 shows three-cross sections of the failed slope.

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