Grain and Pore Scale Insights into Direct Shearing of Partially Saturated Sand

This contribution presents experimental findings from a miniaturised direct shear test on partially saturated sand. The experiment is run inside a computed tomography (CT) scanner (so-called in situ CT experiment) in order to study the influence of shearing on the capillary state. The CT data measured for different displacement increments during direct shearing allow to quantify different capillary state variables on the pore scale as well as to perform an in-depth analysis of discrete grain kinematics. The experimental results indicate a localisation of grain displacements and rotations aligned with changes in the capillary state, including redistributions of pore water as well as changes of capillary water clusters around moving grains, highlighting the strongly coupled hydro-mechanical effects on the pore scale in partially saturated granular soils.