Multi-scale testing and modeling particle size effects on primary and secondary compressibility of crushable granular materials

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Granular fills are widely used in civil engineering and the understanding of their mechanical properties is essential. A key issue in the stress-strain behavior is particle breakage. Briefly, when intergranular contact forces exceed particle strength, a fraction of the particles could crush, changing the grain size distribution towards a finer and more polydisperse material. Consequently, the compressibility increases for a given stress state. Furthermore, particle breakage is the source of size effects and creep strains in granular materials, which could be significant in engineering and geoscientific problems, involving high rockfill dams, pile penetration, granular fills in discontinuities of rock masses, rock fragmentation by weathering, subsidence of fractured rock deposits, among others. Several phenomenological constitutive models for crushable granular materials have been developed according to macro-mechanical observations, based on relationships between the amount of breakage and the compressibility through fitted parameters. However, the source of grain crushing comes from the fracture mechanics of individual grains. In other words, it depends on geometrical and mineralogical characteristics of individual grains, on their loading conditions through particle contacts and on environmental conditions. Therefore, in order to develop physical-based methods, multi-scale approaches seem appropriate, but only a few attempts have been made on this subject and experimental data is quite scarce. In this research program, a comprehensive experimental work and theoretical developments are proposed in order to study the multi-scale mechanisms involved in particle size effects on primary and secondary compressibility of crushable granular materials. The program will allow a broad analysis through micro, meso and macro-scales. Practical applications of this research will be of great interest for geotechnical engineering, as well as other disciplines dealing with the mechanics of granular materials, such as powder technology in the ceramic, pharmaceutical, food and mining industries, for instance.