Collapse Behaviour of Compacted Coal Ashes

Abstract

Coal ash is a by-product produced from the thermal power plants. It is characterized with low unit weight, high shear strength and low compressibility and finds a major application as an alternate material in the geotechnical engineering applications. However, some coal ash fills are susceptible to wetting-induced collapse due to the loss of capillary suction which stabilizes the intergranular bonds. The present study examines the influence of placement conditions, vertical stress and pore fluid concentration on the collapse behaviour of compacted fly ash specimens. The experimental results showed that the maximum collapse potential for the coal ash specimens compacted to relative compaction of 80 % and water content of 15 % was in the range of 8.6-13 % at vertical stress of 100 kPa, which indicates that the apparent preconsolidation stress for the coal ash specimens is equal to 100 kPa. Among the coal ashes, the compacted fly ash specimens are more susceptible to wetting-induced collapse in comparison to bottom ash and pond ash specimens which is attributed to the higher silt size fraction in the fly ash. This study also presents the collapse behaviour of lime stabilized compacted coal ash.