Strength Characteristics of Lime-Treated Pond Ash Towards Mine Void Filling

Abstract

Mine void filling is required to prevent subsequent earth stability difficulties in the form of subsidence. Stream sand and mill tailings have been commonly used since a long period as backfilling materials. On the other hand, with a strict rule prohibiting river sand mining in India, research for emerging alternative engineering materials replacing sand has gained importance.

In India, power generation is mostly dependent on coal based Thermal Power Plant. Pond ash is the mixture of fly ash and bottom ash which are the by-product generated from thermal power plants after the combustion of coal. In the current study, an attempt is made to investigate the feasibility of pond ash as an alternative backfilling material. To achieve the objective, detailed geotechnical and geoenvironmental characterisation of pond ash has been carried out. To assess the strength properties of pond ash mixed with lime, cylindrical specimens were prepared for determining the unconfined compressive strength. The specimens were prepared at four compaction energy. The effect of curing on the strength characteristics of lime treated pond ash was also investigated.

Based on the detailed geotechnical and geoenvironmental characterisation of pond ash, it has been found that pond ash is a lighter, silty size material. Pond ash is slightly collapsible in nature and of low compressibility. Based on lime reactivity test, pond ash is a pozzolanic material. Mostly, the heavy metals (i.e. Fe, Ni, Mg and Zn) are found to be within the permissible limit as per IS 10500 (2012). It has been observed that with an increase in compaction energy, the strength of lime treated pond ash is increased. Significant improvement in the compressive strength were obtained after 28 days of curing time. The lime-treated pond ash may be used as an alternative to sand for backfilling the mine voids.