Overburden dump stabilization over weak floor using rock-filled trench near the toe—a numerical modeling approach

Abstract

In central part of India, there are several reported cases of overburden dump failures in coal mines those directly attributed to presence of weak floor. To improve stability of a dump over weak floor, construction of a rock-filled trench in the soft floor near the toe is studied in this paper using three-dimensional numerical modeling. The effect of a weak floor layer such as black cotton soil or clay on overall stability of an overburden dump is studied for various conditions. The numerical modeling parametric study includes various thicknesses of weak floor layer generally prevalent in central part of India, wet and dry conditions, dump height and various rock-filled trench dimensions practically possible. The study reveals that creating a rock-filled trench with a depth matching with the weak floor thickness increases the factor of safety considerably. The result of the parametric study is useful to optimize the trench volume in a given circumstance in order to achieve the required factor of safety for a dump slope. The study finds that if a dumping surface has a weak floor with a maximum thickness of 10 m the dump can be made as stable as a strong floor scenario by creating an optimally designed rock-filled trench at the final dump toe. The new method has been successfully implemented in some coal mines of central part of India, where the dump height could be increased by 50% and dump volume by 35% within the same dumping area.