Partially saturated media: from DEM simulation to thermodynamic interpretation

Abstract

An extended numerical model of pendular bridge for spherical grains is introduced, enabling the determination of interfacial areas. On this basis, the free energy of interfaces is defined, and its changes are found to balance the mechanical work exerted by the bridge on the particles of a two-grain system, following the first law of thermodynamics. The model enables tracking the changes of free energy in deforming granular systems simulated with the discrete element method. Regular and random packings are simulated to check the dependency between the stress obtained by Love–Weber averaging and the macroscopic deformation. Though frequently supposed to play the role of effective stress in multiphase systems, the Love–Weber stress is found to be a valid effective stress only for regular packings. In random packings, it distinctly differs from the effective stress as evaluated by simulations.