Assumptions in equilibrium analysis and experimentation in unsaturated soil.

The fundamental considerations and assumptions in laboratory equilibrium tests on soils in the triaxial cell are examined using the principles of virtual work and theromodynamics. Compliance with the laws of thermodynamics necessitates that the work energy equation, thus the stresses, maybe derived from the thermodynamic potential. At equilibrium the thermodynamic potential is a minimum and it is shown that this can be written in a similar form for both isotropic and anisotropic loading conditions but for the latter the mean stress replaces the isotropic pressure. The significance of the extensive variable terms making up the thermodynamic potential is also described. The analysis is applicable to soils at any degree of saturation.