Mass utilisation of fly ash as backfilling material in open pit mines – a case study

Abstract

This paper identifies the need of mass utilisation of fly ash in mine, and demonstrates the results of laboratory investigation through numerical analysis understanding the stability of overburden dump formed by mixing with 25% fly ash in opencast coal mine at Raigarh, India. Fly ash generated from the coal based thermal power plant is of great concern due to its disposal. Therefore proper utilization of the fly ash is highly demanded. It is observed that two types of dumps with alternative layer of only fly ash and overburden material, and overburden mixed with fly ash (25%) are found to be stable with safety factor more than 1.2. Geometry of the stable dump has total height of 120 m, 4 number of decks, individual deck height of 30 m, and slope of each deck as 32°. The dump formed with alternate layer of overburden and mixture of fly ash is found stable with a safety factor of 1.78 for the above geometry. Therefore, the above geometry of the back filling material was recommended for the above mine. As a part of reclamation with plantation, top soil of nearly 2 m thick was spread over the dump material in the field. Displacement pattern of the monitoring stations during November 2012 to the end of November 2013 indicated no significant displacement in the Overburden dumps with fly ash ensuring stability of the dump.