Consolidation of large spherical particles at low Reynolds numbers

This study was concerned with the validation of a new theoretical model (Galvin et al., 2015) to describe sediment consolidation, focussing on systems having negligible surface and inertial forces, and hence a minimal compressive yield stress. The study was also concerned with providing a detailed description of this model and its relationship to other work.The particles were assumed to be homogeneous, incompressible and spherical, and to settle in accordance with Stokes` law. The model assumed that the material depositing onto the bed carried three quantities, a fixed portion of solids ΔS, a fixed portion of retained water ΔR, and a variable portion of water deemed to be expressible ΔW. The sediment bed consisted of a finite number of these distinct layers, each containing fixed quantities of the solids and retained water and a variable quantity of the expressible water. The hypothesis of this research was that the reduction in the volume of expressible water declines according to a simple scaling law, ΔW ∝ t^-2. The model was used to describe the entire batch settling curve, concentration profile, and velocity of the particles within the sediment bed. An experimental system was developed to validate the model. Spherical particles of Sephadex were used to form suspensions of a given volume fraction. Conventional batch settling tests were performed, and the height data versus time compared with the model predictions. Other experiments were focussed on the movement of the particles during the consolidation, using a CCD camera to record the settling. Further data on the concentration profiles at different times, for experiments conducted at different volume fractions, were produced. Again very good agreement was achieved between the theory and the experimental data.