SOIL AIR PERMEABILITY - THRESHOLD GRADIENT AND ANISOTROPY

In this study, a triaxial confinement chamber and mass flow meter were used to measure the air permeability of compacted clayey sand specime ns: Specimens were extracted at different angles with respect to the v ertical direction to measure the anisotropy. The soil was compacted at high water contents below the optimum. At lower gradients, deviations from Darcy's law were observed. Threshold gradients were found below which the flow rate-gradient relationship was nonlinear and flow was v ery small. Measurements of anisotropy in air permeability revealed an order of magnitude difference in permeabilities of the specimens extra cted at 0 and 90 degrees with respect to the direction of compaction. The square root of permeability varied in the principal directions acc ording to an ellipse function, although there was significant scatter about the ellipse. The air permeability values obtained from these tes ts were consistent with previously published results.