Compressibility and collapsibility characteristics of sedimented fly ash beds

The fly ash produced from thermal power plants (TPP) is disposed of in the form of slurry into ash ponds, lagoons, or dykes. Fly ash slurry, after undergoing sedimentation and consolidation processes under its own self-weight, exhibits a different engineering behavior than those compacted after dewatering. Literature review indicated no studies are available on the engineering behavior of sedimented fly ash beds/deposits, which is impeding the recycling efforts of the sedimented fly ash beds/deposits. This paper presents test results from laboratory studies conducted on sedimented fly ash deposits prepared by simulating both natural sedimentation and consolidation processes in a prototype environment. A series of compressibility, consolidation and collapse tests were then conducted on specimens collected from the sediment deposits. Test results revealed that the sedimented fly ash material exhibits a pseudoover consolidation effect including a moderate collapsible behavior and an increased compressibility at applied stresses. Collapse potential of the materials ranged between 0.5 and 1%, indicating a metastable fabric of these materials formed in the sedimentation process. Potential engineering behavioral issues related to recycling efforts of fly ash beds are mentioned.