ABSTRACT
The current design criteria for waste containment systems use saturated hydraulic conductivity as a measure of effectiveness of the barrier layers. This, however, can be detrimental to covers in arid and semi-arid regions. In order to achieve a low saturated hydraulic conductivity, the barrier soil must be compacted wet of optimum, which will lead to drying, hence shrinking and cracking, therefore leaving the barrier layer ineffective. These cracks form preferential flow paths, and allow for infiltration of water. In semi-arid and arid climates compacted buffer materials remain unsaturated for a prolonged dry season, therefore suctions are a major factor in influencing the strength, compressibility and hydraulic conductivity of the materials. To minimize the effects of desiccation, clays with lower plasticity should be used, compacted close to optimum water content. Therefore, silty clays, sandy clays, clayey silts and clayey sands are less susceptible to cracking upon desiccation (Benson 1999).
