Application of Terzaghi's consolidation theory to nearly saturated soils

Terzaghi's one-dimensional consolidation theory is modified to account for the compressibility of fluid and solid phases. The proposed modified equations can be used to analyze the consolidation response of unsaturated soils over the saturation range where the gases remain in an occluded form (generally within a range between 80 and 100aturation); however, such applications are subject to the same limitations and idealizations implicit in Terzaghi's classical consolidation theory. The purpose of this note, therefore, is to offer a simple solution and not to unravel the complexities involved in general analysis of flow and deformation response of unsaturated soils. The proposed approach involves defining the consolidation coefficient, and hence the time factor, in terms of an equivalent fluid compressibility. This equivalent fluid is assumed to represent the compressibility characteristics of all the compressible phases that constitute the soil skeleton. The proposed generalized form of Terzaghi's consolidation equations is shown to qualitatively capture the consolidation behaviour of unsaturated soils. To test the validity of the formulations presented, one-dimensional oedometer tests were performed on specimens of Lantz clay that had been prepared at different saturation levels; satisfactory agreement was achieved between the theoretical and measured data at two states of saturation. Key words : consolidation, theoretical solutions, oedometer test, compressible fluid, occluded gas.