CALCIUM AND SODIUM BENTONITE FOR HYDRAULIC CONTAINMENT APPLICATIONS

The hydraulic conductivity of calcium and sodium bentonites was invest igated for sand-bentonite mixtures, a thin bentonite layer simulating a geosynthetic clay liner (GCL), and bentonite-cement mixtures simulat ing backfill for a vertical cutoff wall. The permeant liquids were tap water and distilled water containing 0.25 M calcium chloride. In gene ral, the hydraulic performance of calcium bentonite was not significan tly better than the performance of sodium bentonite for either the cla y-amended sand or the GCL application, and was substantially worse tha n the performance of sodium bentonite in the bentonite-cement mixture. A drained angle of internal friction of 21 degrees was measured for c alcium bentonite, compared to 10 degrees for sodium bentonite. Except for a larger drained shear strength, no advantage of calcium bentonite over sodium bentonite could be identified from the results of this st udy.