High Head Permeability of Sand with Dispersed Clay Particles

High head permeability coefficients of sand‐clay mixtures were obtained for hydraulic gradients that ranged from 5.6 to 408. The sand had a mean diameter of 0.36 mm with a standard deviation of 0.20 mm. The clay constituent was Yazoo formation expansive clay that contained approximately 30% montmorillonite. Clay percentages varied from ½ to 2½%. The addition of 2½% clay at a constant hydraulic gradient of 408 reduced the coefficient of permeability by 56.8%. For the 2½% clay mixture, the coefficient of permeability decreased by 16.6% as the hydraulic gradient increased from 5.6 to 408. The permeability coefficient for pure Columbus sand decreased by 12% as the hydraulic gradient changed from 5.6 to 408.