The effects of water content variation on laboratory samples simulating low permeable clay barriers

Two methods for measuring the hydraulic conductivity of laboratory samples simulating low permeable clay barriers have been used to explore the effects of water content variation on the samples. A silty clay, classified as CH by the Unified Soil Classification System and typical to East Tennessee, from the West Chestnut Borrow Area was used to build the laboratory samples. The flexible-wall permeameter, which used a small scale sample measuring approximately 10 cm (4 in) by 7 cm (3 in) and the lysimeter, which used a field-scale sample measuring approximately 75 cm (29.5 in) by 7.6 cm (3 in) were the instruments used to determine the hydraulic conductivity.

Both sets of samples were subjected to wetting and drying cycles while the density, water content and hydraulic conductivity were measured. The flexible-wall samples had decreased hydraulic conductivity as the samples became denser and drier. The lysimeter sample had an increased hydraulic conductivity as the samples became denser and drier. The predominant differences in the two samples were that the lysimeter samples tended to have preferential flow paths formed during the initial compaction while the flexible-wall samples did not appear to form similar water conduits. Also, during the drying cycles the lysimeter samples experienced cracking which contributed to the increase in hydraulic conductivity while the flexible-wall samples remained intact throughout the drying cycles.

These differences in behavior were due to the fact that the flexible-wall samples behaved as a singular soil aggregate and the lysimeter samples behaved as a group of soil aggregates which acted as a clay barrier.