Résumé
The study of force transmission and typologies of motions in a powder bed under low shear solicitation constitutes a challenging issue to achieve a monitoring of most of processes. This work relies on the characterisation of particle mobility in the neighbourhood of a moving intruder in ascendant vertical motion. Vertical force measurements and Particle Image Velocimetry (PIV) technique are used to identify different typologies of particle motions (compaction, loading and rupture of the chain forces, lateral collapsing, avalanches…) of a granular bed ensiled in a semi-confined cell and with a free surface on its top. Force fluctuations during the blade displacement are highlighted and correlated with the dimensionless blade speed but also with the force profile in the static state. The velocity field analysis allows quantifying the shear-banding characteristics corresponding to the blade influence on grain displacements and the impact of the intruder in the motion direction. This signal contains periodical fluctuations which are correlated with the vertical force fluctuations in a specific zone of the granular bed.