Collapse Behavior of Compacted Coal Ash Fills

Coal ash is widely used in construction of embankments and fills. Compacted coal ash fills are likely to undergo collapse on inundation due to rise of water table or infiltration of rainwater. This paper brings out various factors influencing collapse potential of coal ash. Single oedometer and double oedometer collapse tests and plate load collapse tests were carried out on compacted fly ash (FA), bottom ash (BA), and mixture of fly ash and bottom ash in equal proportion (FA50 + BA50). The results reveal that fly ash is susceptible to collapse, while bottom ash and FA50 + BA50 show negligible collapse. However, a plate load collapse test conducted on compacted ash bed of FA50 + BA50 shows large settlement of plate on inundation. This suggests that the use of the results of single oedometer collapse tests can help estimate only that component of settlement of footing or test plate that is due to compression of the test bed on inundation, and not the total settlement that is due to both collapse compression and shear deformation of the loaded bed.