A theoretical model is presented to predict the moisture flow in an unsaturated soil as tl•e result of hydraulic and temperature gradients. A partial differential heat flo TM equation (for above-freezing conditions) and the two partial differential transient flow equations (one for the water phase and the other for the air phase), are derived in this paper and solved using a finite difference technique. Darcy's law is used to describe the flow in the water phase, while Fick's law is used for the air phase. The constitutive equations •roposed by Fredlund and Morgenstern are used to define the volume change of an unsaturated soil. The simultaneous solution of the partial differential equations gives the temperature, the pore water pressure, and the pore air pressure distribution with space and time in an unsaturated soil. The pressure changes can, in turn, be used to compute the quantity of moisture flow.
The swelling characteristics of statically compacted expansive clays subjected to given isotropic and anisotropic stress conditions were investigated with a triaxial cell apparatus. A unique relationship was found between maximum volumetric swelling and mean normal stresses. From this relationship one can determine a null swelling pressure that will cause neither swelling nor compression or consolidation or both. It was also determined that the maximum axial and radial swelling decrease exponentially with increase in mean normal stress; this relationship is dependent on the principal stress ratio. The swelling ratio (defined as the ratio of axial swelling to radial swelling) was found to decrease with time allowed for swelling, reaching an equilibrium value termed the equilibrium swelling ratio, which is a function of the boundary loading conditions.
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