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The mechanical behavior of a granular medium is closely related to its saturation state. One of the underlying phenomena controlling this dependence is particle breakage. In the presence of water, the strength of a particle is weakened through various physical–chemical processes, which lead to an increase in the intensity of particle crushing. The acceleration of the particles fracturing results in the distinctive mechanical response usually observed in unsaturated soils. A multiscale experimental study was conducted to establish a causal relationship between the change of saturation and the increased breakage rate. Oedometric tests were used to understand the effects of saturation on the mechanics of the granular packing, while crushing and wedge splitting tests help appreciate the micromechanical origins of this typical behavior. [ABSTRACT FROM AUTHOR]

The effect of water on the hydromechanical behavior of unsaturated granular materials has been studied with a micromechanical model based on thermodynamic principles. A general framework based on the theory of thermodynamics with internal variables for constructing thermodynamically consistent multiscale constitutive relations for unsaturated granular materials has been developed. Within this framework, the microscopic total Helmholtz free energy has been separated between a mechanical and a hydraulic part, each of which is a function of either the elastic displacement or the capillary bridge volume and the distance between particles at the microscale. The inter-particle dissipation of energy, assumed to be frictional in origin, is a function of the incremental plastic displacements at the microscale. Both the microscale Helmholtz free energy and the dissipative energy have been volumetrically averaged to obtain the homogenized energy functions at the macroscale. In accordance with the suggested multiscale thermomechanical framework, a micromechanical model has been constructed to describe the behavior of partially saturated granular soils. This model has considered the deformation of soil skeleton by applying a Coulomb-type criterion at the inter-particle contacts. The hydraulic potential is made to be dependent on the size of the particles and is derived through use of the expression for the water retention curve by assuming that liquid bridges are isotropically distributed within the specimen. The performance of the suggested model has been demonstrated through numerical simulations of the behavior of sand under various degrees of saturation and a wide range of mechanical loadings. [ABSTRACT FROM AUTHOR]