DEM SIMULATIONS OF UNSATURATED SOILS INTERPRETED IN A THERMODYNAMIC FRAMEWORK

The behavior of granular materials (e. g. soils) strongly depends on the interactions between particles at the grain scale. In addition, in multiphase systems, the presence of water and interfaces between different phases in the soil adds complexity to the study [1,2,5]. The main purpose of this work is to introduce some concepts that are able to fill the gap between discrete element method simulations [3,4] and thermodynamics in order to develop constitutive laws able to better describe the behavior of unsaturated granular medium. The problem is studied in a thermodynamic framework where energies are calculated at low water content for a simple system of two particles of different sizes connected by a liquid bridge. The effect of gravity is considered to be negligible in this study. The energy supplied to the simple system is divided into two parts: a) the energy due to the change of the matric suction in the system and b) the energy resulting from the movement of the particles with respect to each other. Comparisions with the first law of thermodynamics show that there are some features that have significant importance in the macro formulation of energies. These features may be related to the interfacial areas in the medium.