Clay barrier post compaction water content effects and particle orientation

Two primary theories have been advanced to explain the lower hydraulic conductivity of clay compacted wet of optimum water content. X-ray diffraction analyses of compacted clay was conducted to determine the validity of the particle orientation theory versus the clod theory. These analyses indicated, that the typical kneading compaction method utilized to construct compacted clay barriers, produces a clay fabric which has an essentially random particle orientation. This supports the clod theory. The effect of post compaction water content variations on saturated hydraulic conductivity was also investigated, utilizing kaolinite and flexible wall permeameters. Samples were prepared using modified, standard, and reduced Proctor methods. The initial hydraulic conductivity of each sample was determined. Each sample was progressively dried back from its molding water content, and its hydraulic conductivity was determined after each dry-back. Water content, dry bulk density, volumetric strain, and saturated hydraulic conductivity correlations indicate that strains in compacted clay layers result as the water content varies. These strains may result in aggregation of the clay layer and the subsequent creation of preferential flow paths. Clay placed at lower water contents and higher compactive energies result in less potential strain.