An assessment of selected factors which influence the hydraulic conductivity of fine-grained soils

The in-situ hydraulic conductivity of a compacted soil liner has historically been predicted using laboratory testing methods. The most widely accepted laboratory method for measuring hydraulic conductivity of fine-grained soils is the flexible-wall triaxial cell permeameter method standardized by the American Society for Testing and Materials (ASTM) as ASTM D 5084-90. Factors which influence the laboratory measurement of hydraulic conductivity include method of sample preparation, molding water content, degree of saturation, sample dimensions, type of permeameter, hydraulic gradient, effective stress at outflow end of sample, type of permeant, and growth of microoganisms. Twelve flexible-wall triaxial cell permeameter hydraulic conductivity tests were conducted in general accordance with Method C of ASTM D 5084-90 on an artificial clayey silt (ML) to evaluate the influence of sample length, hydraulic gradient, and test duration. The test results show that 1) relatively long samples exhibit lower hydraulic conductivities than shorter samples, 2) for a given sample length, hydraulic gradient has little to no influence for gradients up to 200, and 3) after approximately one pore volume has passed through the sample, test duration up to approximately six pore volumes of flow shows little influence --Abstract, page iii