The stability of mine waste dump is of vital importance from economic and safety point of view. The internal dumps are composed of a mixture of fragmented rocks and loose soil. Their characteristic is comparable to heavily discontinuous solid mass. The present paper deals with the stability analysis of an internal dragline dump of an opencast coal mine by discrete element method. The discontinuum modelling considerer the discrete nature of the geo-materials found in external overburden dump. The discrete element method uses a circular disk to represent the granular solid mass and their interactions are described by the Newton's third law of motion. The location of crack has been determine and found in the base of the coal rib. The stable slope angle has been determined for present case and width of coal has been varied to understand their effect on stability of dump slope.

1 Introduction

The country's coal production has increased nearly from 431 MT in 2006–07 to 606 MT in 2013–14 (Chikkatur & Sagar 2015 and Thakkar 2014) (an increase of 38.5%). Still, India is importing about 163 MT of coal to fill the country's total demand-supply gap (including coking coal). Total annual coal production from open cast mine is nearly 80%. The production of coal can be enhanced from the existing projects by deployment of mega size Heavy Earth Moving Machineries (HEMMs) as well as to extract the coal seams at higher stripping ratios. However, higher stripping ratios lead to problem of overburden dumps and management, which have posed challenge and leads to danger in terms of safety. The overburden material is either dumped in the pit (internal dump) or dumped outside the pit (external dump). Figure 1 shows a typical layout of internal dumping by dragline as well as a heightened dump using the shovel dumper combination. The overburden is removed with the help of dragline and dumped inside the pit creating an internal dump of a certain height. A coal rib is left between the dragline dump and mine benches.

The stability of internal dump is an important aspect of an opencast coal mining. As the production of open cast mining increases, the amount of overburden increases, larger dump height or high slope angle is opted due to limited dumping space in the mine. This will increase chances of dump slope failure. The coal rib is left to prevent dump material from flowing into working area (Figure 1). A number of cases have been reported when the major dump slides and failures have caused substantial damage and interruption on the production circuit (DGMS circular, 2007).

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