Hydraulic Conductivity of Bentonite Slurry Mixed Sands

The hydraulic conductivity $\left(k\right)$ of specimens from columns containing initially dry sands mixed with bentonite slurries was measured. The mixed specimens represented a range in void ratios $\left(0.672\le e\le 3.94\right)$ and bentonite contents ( $0.61\%\le \mathit{BC}\le 7.65\%$ , by dry weight). The measured $k$ values, which ranged from $2.4\times {10}^{-7}\text{cm}/\text{s}$ to $6.8\times {10}^{-4}\text{cm}/\text{s}$ , correlated poorly with the total void ratio $\left(e\right)$ 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 $\left(e_b\right)$ , 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 $e_b$ in this study $\left(42.5\le e_b\le 127\right)$ was much higher than that previously reported. The relatively large range in $e_b$ 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 $\left(9.4\times {10}^{-3}\text{cm}/\text{s}\le k\le 5.4\times {10}^{-2}\text{cm}/\text{s}\right)$ by as much as four orders of magnitude to values less than $1.0\times {10}^{-6}\text{cm}/\text{s}$ .