Standardized Hydraulic Conductivity Testing of Compacted Sand-Bentonite Mixtures: Fid-Bau Portal

Standardized Hydraulic Conductivity Testing of Compacted Sand-Bentonite Mixtures

Tong, S

Compacted sand-bentonite mixtures can be used as engineered barriers (liners) for waste containment applications. A primary consideration for such applications is the ability of the mixtures to achieve a suitably low hydraulic conductivity, k, typically ≤1.0 × 10−9 m/s, based on permeation with water in the laboratory. The purpose of this study was to evaluate in a systematic manner the applicability of ASTM D5084-10 for the measurement of k of compacted sand-bentonite mixtures. Final degrees of saturation, Sf, for 4 of the 19 test specimens were outside of the required range 95 % ≤ Sf ≤ 105 %, even though the measured k values for these 4 specimens were consistent with those tested under the same conditions with values of Sf that met the standard. Thus, Sf apparently was an unreliable measure of true saturation for the materials tested in this study. Otherwise, the results indicated that conservatively high values of k were measured for the largest specimen size, the highest applied hydraulic gradient, and the highest ionic strength of the permeant water. A difference in the method of hydraulic gradient application had essentially no effect on the magnitude of k. Finally, as expected, specimens containing the highest amount of bentonite (i.e., 15 % by dry weight) resulted in the lowest values of k, although calculation of some values of k for one specimen were negative (k < 0), which was attributed to swelling of the specimen during permeation and the manner in which k was calculated based on ASTM D5084-10.