Permeability changes due to volumetric dilation and shear band formation in sands under triaxial loading

Various mechanisms can affect the permeability of dense unconsolidated sands: volumetric dilation can lead to permeability increase whereas strain localization in shear bands may increase or decrease the permeability depending on the state of compaction and on the level of grains breakage inside the band. In order to investigate these various mechanisms, an experimental study has been performed to explore the effect of different factors such as grain size and grain shape, confining pressure, the level of shear, and the formation of one or several shear bands on the permeability of dense sands under triaxial loading. The experimental results show a reduction of permeability during the consolidation phase and during the phase of volumetric contraction of shear loading which can be related to the decrease of porosity. The experimental results also show that, depending on the confining pressure, the permeability remains stable or decrease during the phase of volumetric dilation despite the increase of the total porosity. This permeability reduction is attributed to the presence of fine particles which result from grains attrition observed during pre-localization and grains breakage inside the shear band observed during the post-localization phase.