Modeling Volume Change and Mechanical Properties with Hydraulic Models

Volume change of soils may be caused either by external (mechanical) or internal (hydraulic) stresses or a combination of both. A complete description of volume change must therefore include both mechanical and hydraulic stresses. By coupling theories of mechanical and hydraulic stress states, a hydraulic function, which predicts the change of water volume as a function of the stress state parameter soil water suction (water retention curve), is adopted to model volume change. The utilisation of such a continuous function also enables the derivation of soil mechanical parameters (e.g. pre-consolidation stress, Youngs modulus) by determining mathematically the point of maximum curvature and inflection point. This information can then be used to calculate the pre-consolidation stress according to the method of Casagrande. The presented calculation has considerable advantages compared to the graphical method of Casagrande or other methods. On the basis of stress-strain relationships of various textured and structured soils and soil substrates and various test procedures (oedometer test, triaxial test; shrinkage test) volume change is modelled using the described method. It is shown, that modelling volume change by e.g. the van Genuchten equation using the software RETC is possible with high accuracy. Soil mechanical parameters are derived using the paramters of the van Genuchten equation.

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