Abstract
A novel approach has been developed to predict the mechanical behavior of very coarse granular materials with a constitutive model, which considers both grain breakage and size effect. The behavior of granular assemblies is significantly influenced by particle breakage. A critical-state double-yield-surface model incorporating the change in the critical-state line and in elastic stiffness caused by grain breakage during loading has been adopted. The amount of grain breakage was estimated by extending the size effect theory on individual grains to granular assemblies. The results from earlier studies on granular materials with parallel gradations have been usefully exploited to calibrate and to validate the model. Comparisons between experiments and simulations suggest that this approach can predict the mechanical behavior of very coarse granular materials from test results performed on a finer fraction with a homothetic gradation.
Highlights
The construction of large civil engineering works involving coarse grained materials, such as rockfill dams, is increasing worldwide
The results demonstrate that at higher stress levels the amount of grain breakage is greater, and, as a consequence, the size effect is more pronounced on both the shear stiffness and the maximum strength
The authors constructed a constitutive model able to reproduce the main features of granular materials
Summary
The construction of large civil engineering works involving coarse grained materials, such as rockfill dams, is increasing worldwide. Eref or pref is the only variable necessary to control the evolution of the critical-state line, if one can assume that the slope remains constant regarding to very similar form of grains before and after grain crushing for natural sand by Biarez and Hicher (1997). Pref corresponding to a fixed value of eref 1⁄4 0.5 was adopted to describe the evolution of the critical-state line caused by grain breakage; the following expression is suggested: pref 1⁄4 pref0 expð−bBÃr Þ ð15Þ where parameter b controls the rate of the CSL shifting caused by grain breakage. According to Eq (21), the crushing forces of each particle (fGi) are related by fG2 If both granular materials present the same amount of grain breakage after shearing, the stress magnitude on G2 should be lower because coarse grains have lower strength. To model the behavior of a given coarse granular material, it is possible to select a finer homothetic grain-size distribution to prepare a representative finer material whose grain sizes are compatible with the available experimental means of the laboratory
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