The flow-out potential of a body of fluidized sediment following abrupt collapse is discussed through numerical and physical modelling. The emphasis of the analysis procedure is placed on considering density stratification that occurs in highly concentrated sediment gravity flows. Specifically, it combines Navier-Stokes/continuity equations for a liquefied soil domain with a consolidation equation for the underlying, progressively solidifying soil domain. Evolutions of the flow and solidification surfaces are traced as part of the solution using a volume-of-fluid (VOF) technique. The physical modelling is concerned with two-dimensional flume tests, together with related fluidization and sedimentation tests under onedimensional conditions. A body of fluidized sandy sediment was subjected to abrupt collapse and allowed to flow out into ambient water. The observed and calculated results show that the highly concentrated sediment flow manifests itself as a decelerating gravity flow due to interactions between the flowing fluidized sediment and accreting soil with a grain-supported framework being reestablished.