Predicting Incipient Fluidization of Fine Sands in Unbounded Domains

Abstract

From the theory of flow through porous media, the governing equation for hydraulic head is developed for flow emanating from small holes in a pipe buried in fine sand in the coastal environment. Calculated Reynolds numbers for sand grain sizes typically found in tidal inlets (less than 0.5 mm) indicate that the generalized Darcy law remains valid up to fluidization. The head distribution in the domain is obtained from the two‐dimensional finite element method and validated with experimental results. The theoretical critical hydraulic gradient is used to predict the incipient fluidization flow rate conditions for the available experimental data as well as for a wide range of field situations. A practical fluidization‐system chart is developed for determination of the flow rate required for incipient fluidization. For a pipe diameter of 0.3 m, the chart provides flow rates for burial depths ranging between 1.5 and 12.2 m. The head loss through the bed at incipient conditions is 1.9–2.9 times the bed depth for the range of simulated conditions.