Weathering-induced fissuring and hydraulic conductivity in a natural plastic clay

Flexible-wall (triaxial) permeability tests have examined how laboratory-induced weathering affects the hydraulic conductivities of "undisturbed" specimens of a high-plastic expansive natural clay. After freezing-thawing or drying-wetting, hydraulic conductivities were on average about one order of magnitude higher than unweathered values. Reductions of hydraulic conductivity occurred in some specimens that were dried and then rewetted before permeation. The generally small changes in hydraulic conductivity are attributed to the expansive nature of the clay which allows swelling and reorientation of soil aggregates on thawing or rewetting. The changes may also have been influenced by the confining pressures of 35 kPa used in the tests. Hydraulic conductivities measured by oedometer were smaller than those in triaxial tests and varied strongly with pressure level.Key words: hydraulic conductivity, clay, plastic, weathering, desiccation, freezing.