Compacted clay liners and covers for arid sites

Tests were performed on a clayey soil from a site in Texas to define ranges of water content and dry unit weight at which compacted test specimens would have: (1) low hydraulic conductivity; (2) minimal potential for shrinkage upon drying; and (3) adequate shear strength. Test specimens were compacted with three compactive energies over a range of water content. Low hydraulic conductivity could be achieved over a broad range of water content, but relatively wet specimens underwent large shrinkage upon drying. A range of water content near the optimum value measured with the highest compactive energy proved to be suitable in meeting the objective of low hydraulic conductivity and shrinkage potential. The dry unit weight had to be greater than 96-98% of the maximum value from modified compaction (ASTM method D1557) to meet hydraulic conductivity, shrinkage, and strength objectives. A similar approach is suggested for development of compaction criteria at other projects in which low-hydraulic-conductivity liners or covers must be constructed in relatively arid regions or other situations in which potential cracking caused by desiccation is of concern