No abstract

A new elastoplastic stress–strain constitutive model is developed for granular coarse aggregates incorporating the degradation of particles during triaxial shearing. Coarse granular aggregates are subjected to breakage during excessive stress changes. Most of the available constitutive models do not consider the degradation of particles during shearing. In the current model, a plastic flow rule has been developed incorporating the energy consumption due to particle breakage during shear deformation. A non-associated flow and a kinematic type yield locus have been adopted in the model. A general formulation for the rate of particle breakage during shearing has been developed and incorporated in the plastic flow rule. The effects of particle breakage on the plastic distortional and volumetric deformations are incorporated in the current model. The stress–strain formulations are developed within the general critical state framework. The model can accurately predict the stress–strain and volume change behaviour of coarse granular aggregates. The plastic dilation and contraction features of coarse aggregates at various confining pressures are well captured, and the strain-hardening and post-peak strain-softening behaviour of coarse granular media is adequately represented. A particular feature of the model is its capability to predict the degree of particle breakage at any stage of shear deformation.Key words: constitutive modelling, coarse granular aggregates, particle breakage, dilatancy, non-associated flow, plasticity.

The ballast and its engineering behaviour have a key role in governing the stability and performance of railway tracks. The deformation and degradation behaviour of ballast under static and dynamic loads was studied based on large-scale triaxial testing. The possible use of different types of geosynthetics to improve the performance of fresh and recycled ballast was also investigated. The research findings showed that the inclusion of geosynthetics improves the performance of ballasted tracks.Keywords : geosynthetics; large-scale triaxial testing; railway ballast Le ballast et son comportement mécanique ont une influence importante sur la stabilité et la performance des voies ferrées. Nous avons étudié le comportement de détériora-tion et de déformation du ballast sous charge statiques et dynamiques en nous basant sur des essais triaxiaux à grande échelle. Nous avons également étudié la possibilité d'utiliser divers types de géosynthétiques pour améliorer la performance du ballast neuf et recyclé. Les résultats de cette recherche ont montré que l'adjonction de géosynthé-tiques améliorait la performance des voies ballastées.

The degradation of coarse aggregates under shear stresses and its influence on the shear strength is studied, considering the energy consumption by particle breakage during shearing. An analytical model is developed relating the deviator stress ratio, dilatancy, friction angle and particle breakage under triaxial loading. Large-scale triaxial testing of latite basalt has been conducted, and the extent of particle breakage during shearing has been quantified. The breakage of particles under monotonic triaxial loading has been considered within the scope of this paper, and the modelling of particle breakage of aggregates under cyclic loading will be presented in a follow-up paper. The results show that the breakage of particles continues to increase beyond the peak deviator stress. The energy consumption by particle breakage is non-linearly related to the particle breakage index. The model also evaluates the effect of particle breakage on the friction angle of ballast. This study sheds further light on the basic angle of friction, which is independent of the breakage of particles during shearing.

No abstract