Modeling the effect of wetting on the mechanical behavior of crushable granular materials

It is well known that the compressibility of crushable granular materials increases with the moisture content, due to the decrease of particle strength in a humid environment. An existing approach to take into account the effect of grain breakage in constitutive modeling consists in linking the evolution of the grain size distribution to the plastic work. But how the material humidity can affect this relationship is not clear, and experimental evidence is quite scarce. Based on compression tests on dry and saturated crushable sand recently reported by the present authors, a new non-linear relationship is proposed between the amount of particle breakage and the plastic work. The expression contains two parameters: (1) a material constant dependent on the grain characteristics and (2) a constant depending on the wetting condition (in this study, dry or saturated). A key finding is that the relationship does not depend on the stress path and, for a given wetting condition, only one set of parameters is necessary to reproduce the results of isotropic, oedometric, and triaxial compression tests. The relationship has been introduced into an elastoplastic constitutive model based on the critical state concept with a double yield surface for plastic sliding and compression. The breakage ratio is introduced into the expression of the elastic stiffness, the critical state line and the hardening compression pressure. Incremental stress-strain computations with the model allow the plastic work to be calculated and, therefore, the evolution of particle crushing can be predicted through the proposed non-linear relationship and reintroduced into the constitutive equations. Accurate predictions of the experimental results in terms of both stress-strain relationships and breakage ratio were obtained.