Impact of the fines content on stress fluctuations in bi-disperse granular mixtures during triaxial tests

In this experimental study, the influence of fines content and specimen preparation method on the mechanical behavior of granular mixtures have been explored by studying stress fluctuations that occur when the mixtures are subjected to drained triaxial tests. The magnitude and distribution of stress fluctuations are related to the changes in the microstructure of the ensemble. Bi-disperse granular mixtures of glass beads with a size ratio of 8.8, over the entire range of fines content Fc (0% to 100%) were considered. The specimen were prepared using two standard specimen preparation techniques, dry deposition and moist tamping to recreate two distinct microstructures. It is found that in the under-filled regime where the stress transmission is mainly governed by the coarse particles, a significant increase in the magnitude of fluctuations is observed as the fines content, Fc, increases, and on the contrary in the overfilled regime, where the load bearing structures are mainly made up of fines, fluctuations are found to decrease with further increase in FC which suggests that larger the interplay between coarse and fine particles, larger the fluctuations. Further investigation of these fluctuations in the context of critical avalanche dynamics or Self Organized Criticality (SOC) is performed.