Long-term strain records obtained in large-diameter oedometer tests on compacted gravels demonstrated that strains could be linearly related with the logarithm of time. Delayed compressibility coefficients were found proportional to the conventional stress-induced compressibility coefficients. A framework rooted on the phenomenon of crack propagation in rock particles induced by stress corrosion mechanisms is adopted to explain macroscopic observations. A model of crack propagation in loaded disc-shaped particles has been developed in order to explain the nature of particle breakage and its relationship with time, macroscopic stress and total suction. Experimental observations such as the existence of threshold stresses that mark the onset of delayed deformations are explained by the model. It was also found that the main features of the delayed deformation of rockfill could be physically explained within the developed framework. In particular, a simple closed-form relationship between the coefficient of delayed deformation, the compressibility coefficient and a parameter describing the rate of crack propagation could be found. It was found to be consistent with experimental observations.

Rockfill stress-strain behavior is strongly controlled by the breakage of rock particles. Particle breakage is shown to depend on stress level and the ambient relative humidity. A technique to perform tests on rockfill samples under relative humidity control has been developed. It has been applied to testing large diameter samples of a crushed quartzitic shale under oedometric conditions. Relative humidity is imposed by means of a double stage approach: moist air in thermodynamic equilibrium with a given saturated salt solution is first circulated through the sample. Circulation of moist air is interrupted and the specimen is allowed to reach equilibrium. A technique to extend the feasible suction range of the technique down to 2.5 MPa is described. Details of the evolution of collapse and swelling/shrinkage strains, as changes in Relative Humidity are imposed, are reported in the paper. Experimental findings are consistent with an underlying mechanism of particle breakage explained by the phenomenon of subcritical crack propagation.

The paper presents a macroscopic constitutive model for rockfill that includes the effect of water on compressibility and collapse phenomena. Breakage of rock particles and fracture propagation are basic underlying mechanisms controlled by the relative humidity of the air filling the rockfill voids. A conceptual deformation model based on these mechanisms is first proposed and discussed. The results of oedometer tests on a quartzitic slate rockfill, in which the air relative humidity was controlled, are then presented. A significant finding is that bringing the relative humidity within the specimen to its maximum (100% RH) leads to a collapse strain equal to that observed in flooded specimens. An elastoplastic constitutive model, consistent with the basic deformation framework, is developed. Its parameters have a clear physical meaning. Guidelines for parameter determination are given. Model performance is finally compared with the results of the experimental programme. L'article présente un modèle macroscopique de comportement des matériaux d'enrochement. Il prend en compte l'influence de l'eau sur les phénomènes de compressibilité et de collapse. Les mécanismes fondamentaux sous-jacents considérés sont le broyage et la propagation de la fracture à l'intérieur des particules, controllés par l'humidité relative de l'air remplissant les vides du matériau d'enrochement. Un modéle conceptuel de déformation est premièrement proposé et discuté sur la base de ces mécanismes. Des résultats d'essais oedométriques à humidité relative contrôlée réalisés sur des enrochements d'ardoise quartzitique sont ensuite présentés. Un résultat important est le fait que la déformation de collapse obtenue par augmentation de l'humidité relative jasqu'à une valeur de 100% est la même que celle observée par inondation de l'échantillon. Un modèle élastoplastique cohérent avec le cadre conceptuel de déformation proposé est alors développé. Ses paramètres ont une signification physique claire et la ...