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Investigations of wall effect on permeability through porous media at low flow rates

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The study of percolation of fluids through permeable subsoil strata has always been a subject of great significance from engineering point of view. The permeability depends upon both material properties and fluid characteristics. Previous studies are concentrated on the influence of regularly shaped particles on permeability, whereas the present study aims to analyse its variation due to natural randomly shaped particles. Seepage velocity of the fluid and hydraulic gradient of the soil bed materials are evaluated with the help of discharge and pressure measurements in a constant head permeameter. Specific gravity tests are conducted on different materials in order to calculate their porosities. The dependence of permeability on Dp/dg (i.e. ratio of permeameter size (Dp) to particle size (dg)) for various wall effect conditions is analysed through standard experimental procedures. The present study examines the effect of relative resistance of permeameter wall (i.e. the ratio of permeability of confined to unconfined bed) on Dp/dg. The results reveal that the aquifer confinement i.e. the distance up to which the region of randomly packing occurs directly influences the measure of permeability at lower values of Dp/dg. This effect decreases with increasing values of Dp/dg and becomes negligible at values 120 and above.

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