  The rheology of granular materials near an interface is investigated through
proton magnetic resonance imaging. A new cylinder shear apparatus has been
inserted in the MRI device, which allows the control of the radial confining
pressure exerted by the outer wall on the grains and the measurement of the
torque on the inner shearing cylinder. A multi-layer velocimetry sequence has
been developed for the simultaneous measurement of velocity profiles in
different sample zones, while the measurement of the solid fraction profile is
based on static imaging of the sample. This study describes the influence of
the roughness of the shearing interface and of the transverse confining walls
on the granular interface rheology.
