Volume 7, Issue 4 (December 1984)
Laboratory Evaluation of Soil Suction Components
A laboratory evaluation of the soil-water potential components (total, matrix, and osmotic suction) is presented using a series of clay specimens statically compacted dry- and wet-of-optimum. In unsaturated soils, moisture movement is controlled either by total or matrix suction depending upon the degree of unsaturation, whereas deformation and strength behavior is controlled primarily by matrix suction. Therefore, it is imperative to evaluate the suction components separately. Significant osmotic suction component was induced as a result of incomplete leaching of the sodium and calcium surface-saturated Grundite (initially prepared by treating the clay slurry with strong sodium chloride and calcium chloride solutions to achieve mass action of cations). Matrix suction was induced by equilibrating the specimens to different pressures on a ceramic-plated extractor. At equilibrium, total suction of the specimens was measured using a Peltier type psychrometer. Test results indicate the use and limitations of the psychrometric method and the interrelationship of suction components. Measured values of the total suction by the psychrometric method indicate more consistent results at moisture contents above the plastic limit. Below the plastic limit, the osmotic component, as deduced by the difference between total and induced matrix suctions, tends to decrease gradually with increasing matrix suction. It is found that the osmotic suction can be measured most suitably on pore-water extracts using psychrometry.