An experimental investigation of the relationships between grain size distribution and shear banding in sand

This paper experimentally investigates the possibility to describe the influence of microstructure on shear banding in sand in terms of grain size distribution. Different gradations of the same sand were tested, differing from each other in terms of both the mean grain size and uniformity. Monodisperse sands as well as binary mixtures were tested. Water-saturated specimens of the different sands were tested in plane strain under drained conditions, starting from high relative densities. False relief stereophotogrammetry was used to capture the onset of strain localization and for accurately measuring the width and orientation of shear bands. Results from a total of 11 tests are summarized herein. The influence of mean grain size and grain size distribution uniformity on the occurrence of strain localization and shear band thickness and orientation is discussed. While the results confirm the dependence of the band thickness on the mean grain size, they demonstrate that the orientation of a shear band is not related to the mean size of sand particles size, in contradiction with previous experimental findings. Moreover, shear band orientation can neither be simply related to the uniformity of sand grading. The major result of this study is that while grain size distribution can greatly affect shear banding characteristics, there is not such a thing as a direct relationships between characteristics of localization and mean grain size, or degree of uniformity, or other parameters describing grain size distribution in a simple way. Sand microstructure is a key factor yet its influence on shear banding cannot be described in terms of grain size distribution only.

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