Predicted and measured hydraulic conductivity of sand-sized crushed limestone

The hydraulic conductivity of 54 sand-sized crushed limestone materials was measured by conducting constant head tests in a rigid-wall permeameter and was estimated using six predictive equations requiring easily obtainable parameters. The gradations tested had effective grain size, D₁₀, from 0.079 to 2.15 mm; uniformity coefficient, C_u, from 1.19 to 15.79; and void ratio, e, from 0.42 to 0.76. The measured hydraulic conductivity had a range of about three orders of magnitude (3.4*10⁻³ to 3.3 cm/s). Four of the predictive equations, based on the square of the effective grain size, D₁₀², yielded closely grouped results differing by not more than a factor of 2. Long existing equations by Terzaghi (1925) and by Hazen (1892), adjusted for void ratio according to Taylor (1948), were found to have a high predictive efficiency with a ratio of predicted to measured values between 1/2 and 2 for 70% of the materials tested. The Kenney et al. (1984) equation, based on D₅², was also efficient but underestimated measured values for 63% of all cases. The Kozeny–Carman equation (Taylor 1948; Chapuis 2012), based on specific surface, overestimated measurements for 90% of the tested materials by a factor of up to 3.