Investigating the Use of Centrifuge Modeling and Miniature CPTs to Characterize the Run-Out Behavior of Fly Ash

Understanding and characterizing the mechanical behavior of fly ash underpins the continued maintenance, risk assessment, and planning of closure procedures for fly ash ponds. Saturated fly ash can undergo flow failure or static liquefaction that exacerbates the consequences of an impoundment failure, such as the run-out of large volumes of ash. Dewatering of fly ash deposits is a potential mitigation technique that may reduce impacts of material run-out. This paper presents results from miniature CPT soundings from centrifuge models of fly ash deposits performed prior to the simulated failure of the containing structure. The tests feature variations to the initial deposit density and were fully saturated or dewatered in flight. Normalization of the measured cone resistances is shown to help address experimental uncertainty of the initial deposit density. Further, combining the results from CPTs performed at different penetration rates reveals whether the volume-change tendencies of the ash is contractive or dilative. These findings can be related to the observed run-out behavior, in terms of run-out distance and failure mechanism, and thus risk posed by failure of the containing structure. Ultimately, the dependence of the impoundment stability on the deposit density and potential improvement arising from dewatering, in addition to the use of CPTs to quantify these changes, is highlighted.