Centrifuge Test Data from Fly Ash Deposits Subjected to a Loss of Confinement

Numerous industries are concerned by the humanitarian, environmental, and economic consequences
of debris flows, landslides and material run-outs. However, the run-out behavior following a loss of
confinement e.g., dam failure, is not well understood. The material’s complex constitutive behavior
means multiple mechanisms contribute to the deformation e.g., slope instability, seepage forces, erosion
or static liquefaction. In this study, centrifuge models of fly ash deposits, with varying initial deposit
density and water table height, were subjected to a rapid loss of lateral confinement. Deformation,
pore pressure and water content measurements were used to investigate and separate the mechanisms
governing the run-out. Static liquefaction was observed in deposits initially looser than the critical state
and led to a rapid material outflow. Slope instability was the initial failure mechanism for denser deposits
or those with reduced water tables, with transient stability due to dilation-induced negative excess pore
pressures followed by progressive failures caused by seepage pressures from drainage and pore pressure
dissipation. Cone penetration tests, performed before loss of confinement and with different penetration
rates, characterized the material run-out and volume change tendencies and may be a practical tool for
assessing the run-out risk of deposits in the field.