Study of Stability of Overburden Dumps Mixed with Flyash in an Opencast Coal Mine

Abstract

The huge quantities of fly ash generated in India (131.09 mn tonnes in 2010-11) by the coal fired thermal power plants every year raises a serious question about its disposal along with the difficult issues of land availability and pollution of local environment. According to MoEF guidelines any mine within 50 km from a power plant has to use at least 25% of its backfill as fly ash. In this project the stability of overburden dumps mixed with fly ash in KTK opencast mine of SCCL has been studied. Samples of overburden and fly ash were collected from KTK mine and APGENCO, Chelpur respectively. Different geo-technical parameters i.e. density, cohesion and friction angle of OB mixed with 15% and 30% fly ash were found out. Using those parameters, dumps of 30 m height were modelled in FLAC SLOPE software to find out the safe slope angle i.e. angles for which the factor of safety is greater than 1.2. The following results were obtained for different mixes of fly ash and OB: Soil Angle FoS OB 29 1.22 OB + 15% fly ash 26 1.22 OB + 30% fly ash 28 1.22 The initial decrease in slope angle from 29º to 26º with the addition of 15% flyash might be attributed to the inadequate packing of voids between OB particles by the finer sized flyash particles With increasing quantity of flyash i.e. at 30%, packing of the voids would become more compact as they reduce the void ratio. This would lead to the increase in slope angle obtained with OB + 30% fly ash from 26 º to 28º. However, there was no significant change in slope angle with addition of flyash vis-à-vis OB.