Geotechnical Characterization of Indian Coal Ash: A Review

Bottom ash and fly ash are the main residual products generated from the burning of coal in the thermal power plants. Fly ash and bottom ash are mixed with large quantity of water and stored in the ash pond. Ash pond breaches are a major concern for engineers as well as localities residing near ash ponds. Bad characterization of coal ash material may be the primary reason for such failures. A proper geotechnical characterization of coal ash is required to assess an ash pond's short-term and long-term stabilities and its effective use in various geotechnical applications like filling of low-lying areas, construction of highway embankments, dykes, etc. This paper reviews the applicability of the critical state soil mechanics approach to characterize coal ash. Furthermore, an extensive review has been done on coal ash’s mineralogical, morphological, engineering characterization and Indian ash pond breach. The review suggests that the Indian coal ash possesses less specific gravity leading to lower unit weight. Coal ashes exhibit non-plastic behavior, classified as sand to silt. XRD results show that coal ash consists of quartz and feldspar minerals and exhibits crystalline and amorphous phases. Coal ash's hydraulic conductivity is similar to fine sand/silt mixtures or silt. The characteristics of normal compression line (NCL) and critical state line (CSL) in \(e - \ln P^{\prime}\) space are similar to that of granular soils with few exceptions.