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.

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.

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The paper presents a macroscopic constitutive model for rock®ll 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 ®lling the rock®ll voids. A conceptual deformation model based on these mechanisms is ®rst proposed and discussed. The results of oedometer tests on a quartzitic slate rock®ll, in which the air relative humidity was controlled, are then presented. A signi®cant ®nding is that bringing the relative humidity within the specimen to its maximum (100% RH) leads to a collapse strain equal to that observed in¯ooded 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 ®nally compared with the results of the experimental programme.

No abstract