Effect of Bentonite on Compacted Clay Landfill Barriers

Compacted clay barriers (liner and cap) are one of the most important components of municipal waste landfills. On-site soils are generally used to construct the clay barriers as long as they can be compacted to standard specifications, including hydraulic conductivity. Wherever the available on-site soils are not suitable to be used for constructing clay barriers, soils amended with bentonite are commonly used. This article presents the results of an experimental study conducted on compacted clay-bentonite mixtures to develop data on the effects of bentonite on engineering properties of compacted clay-bentonite mixtures. Clay-bentonite mixtures with bentonite contents of up to 7% were tested to determine consistency using Atterberg limits, moisture-density relationships using standard Proctor compaction tests, shear strength using unconfined compression tests, hydraulic conductivity using triaxial flexible-wall hydraulic conductivity tests, and consolidation properties using one-dimensional consolidation tests. Unconfined compression tests were also performed with 11% bentonite content. The laboratory test results indicated that liquid limit, plastic limit, and plasticity index increased linearly with increased amount of bentonite. The addition of bentonite resulted in decreased maximum dry unit weight but the optimum moisture content increased slightly. Unconfined compression strength of compacted clay-bentonite mixtures increased linearly with an increase in the amount of bentonite. Hydraulic conductivity of compacted clay-bentonite mixtures decreased nonlinearly with increased amount of bentonite, but a linear relationship was observed between logarithm of hydraulic conductivity and bentonite content. The compression index increased slightly from 0 to 3% bentonite content but increased nonlinearly beyond 3% bentonite content, whereas the swelling index of clay-bentonite mixtures has been observed to increase approximately linearly with increase in the amount of bentonite.