Abstract
The equation governing the unsaturated transient flow in a soil sample when subjected to suction (ψ) at its base and that of the classical 1-D consolidation are exactly alike (equation of diffusion). The former can be arrived at by Richards’ equation, being in this case the moisture diffusivity (D), instead of the coefficient of consolidation (cv), the governing parameter. D need not be constant, but rather a function of the volumetric water content, D=D(θ), and is defined as the ratio of the hydraulic conductivity, k(θ), over the specific water capacity, C(θ)=dθ/dψ, i.e., the slope of the SWRC. The hyperbolic method has been used for several geotechnical purposes and, most importantly, as an alternative to Asaoka’s method for predicting the final settlement and cv of soft soils undergoing consolidation, improved by preloading. This paper shows that both methods prove to be very useful as a means of obtaining D(θ) and k(θ) at a certain range of θ, provided that a reduced number of water contents at known elapsed times are determined over the medium stage of this transient flow. It is addressed in the paper both by theoretical grounds and on the light of experimental data of 4 soils.
Highlights
When the base of an unsaturated soil sample is subjected to a source of suction, irrespective of the technique used, an unsteady flow of water towards a new equilibrium is established
Due to the difficulty of assessing a global value of cv, and the final settlement (δ∞) of a site on soft soils subjected to a surcharge, a few predictive methods are proven to be useful, as long as a number of measurements over the medium stage are available
Assuming the identity of the governing equation of the described unsaturated flow and a 1-D consolidation process, such predictive methods can be extended, mutatis mutandis, to predict the final water content of the sample subjected to certain suction, and more importantly, its moisture diffusivity (D)
Summary
When the base of an unsaturated soil sample is subjected to a source of suction, irrespective of the technique used, an unsteady flow of water towards a new equilibrium is established. This process is governed by the equation of diffusion, just like the heat transfer or, in the scope of soil mechanics itself, a process of consolidation, where the coefficient of consolidation (cv) plays the same role as the moisture diffusivity (D). Assuming the identity of the governing equation of the described unsaturated flow and a 1-D consolidation process, such predictive methods can be extended, mutatis mutandis, to predict the final water content of the sample subjected to certain suction, and more importantly, its moisture diffusivity (D). A reduced number of water contents at different elapsed times would suffice for these two methods to be applicable
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