The analysis of wetting and consequent swelling of unsaturated clays requires the specification of water potential in the unsaturated regime. Conventional characterization of water potential in unsaturated soils is done in terms of "retention curves" that specify a relation between suction and water content. In all conceptual models of unsaturated soils, suction is assumed to depend on the geometry ofthe "water-filled pore space." A first order characterization of this geometry is proposed in terms of water content, void ratio, and initial conditions. Despite this fact, conventional retention curves are presented as a relation between suction and water content, regardless of the void ratio. Moreover, in conventional laboratory techniques for the determination of suction there is no control over the void ratio, and each point on the retention curve corresponds to a different void ratio if swelling soil is tested. The present paper presents a laboratory technique for the determination of suction as a function of water content, void ratio, and initial conditions. Preliminary experimental results show that void ratio may have a substantial effect on suction, particularly in the low suction range. It is also demonstrated that the dependence of suction on void ratio has a significant effect on the analysis of the flow and swelling processes, to the extent that use of conventional suction curves in the analysis may lead to unreasonable results. This paper appears in transportation research record no. 1277, Modern geotechnical methods: instrumentation and vibratory hammers 1990.
Abstract