Hydraulic Conductivity of Bentonite Slurry Mixed Sands

Abstract

The hydraulic conductivity (k) of specimens from columns containing initially dry sands mixed with bentonite slurries was measured. The mixed specimens represented a range in void ratios (0.672≤e≤3.94) and bentonite contents (0.61%≤BC≤7.65%, by dry weight). The measured k values, which ranged from 2.4×10−7 cm/s to 6.8×10−4 cm/s, correlated poorly with the total void ratio (e) of the specimens, due to the complicating effect of the bentonite in the sand-bentonite slurry mixtures. However, the measured k values correlated better with the void ratio of the bentonite (eb), which is consistent with the results of previous studies involving permeation of compacted bentonite and sand-bentonite specimens, even though the range in values of eb in this study (42.5≤eb≤127) was much higher than that previously reported. The relatively large range in eb values for the sand-bentonite slurry mixtures was also consistent with the relatively large range in measured k values, which are about one to seven orders of magnitude higher than values of k commonly reported for compacted sand-bentonite mixtures, despite similar bentonite contents. In terms of bentonite content, addition of more than 3% bentonite via slurry injection and mixing with the sands was successful in reducing the k of the unmixed sands (9.4×10−3 cm/s≤k≤5.4×10−2 cm/s) by as much as four orders of magnitude to values less than 1.0×10−6 cm/s.