Abstract:

A very complex slope failure took place at an open-pit coal mine in 1984 in the eastern Turkey. The earlier investigations showed that a basal clay layer at the bottom of the coal seam was the main cause of the failure. The failure took place while the coal seam was uncovered. In this study, a series of back analyses utilizing the information of geotechnical investigations before and after the failure and static and dynamic limiting equilibrium techniques and finite element analyses were performed, and their outcomes are presented and discussed. It is shown that the failure process was complex and involved the buckling of the lignite seam, sliding along the basal clay layer and shearing failure of overburden layers. The drainage conditions also played an important role in the initiation of the failure. Once the failure as initiated, the failure developed rapidly.

1 Introduction

The failure of slopes during mining operations results in not only loss of the mining machinery but also human lives which make the mining operations become very costly. Therefore, a good design is necessary before the initiation of mining operations since any change of design later on will result in high cost and time loss.

A very complex failure took place at the northeastern slope of the Kışlakóy 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 (Ulusay et al. 1986).

In this paper, the authors re-consider the 1984 failure from another point of view. Previous analyses for the assessment of stability of these slopes were based on combined failure surfaces partly passing through the slope forming materials and partly along the basal clay layer (Ulusay et al. 1986). Examining the photographs of the failure, the heaved lignite seam shows a set of buckles. Based on this issue, the failure was re-examined by considering also the possibilities of buckling failure and compressive failure of the coal seam which constitutes the pit floor. For this purpose, a series of back analyses utilizing the information of geotechnical investigations before and after the failure, and static and dynamic limiting equilibrium techniques and finite element method were performed. The outcomes of these analyses are presented and discussed.

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