The aim of this colloquium is to gather the European scientific community to exchange on recent developments regarding the coupling mechanisms in granular fluid-flows at different scales, from that of the single grains to that of the mesoscopic deformation of an assembly of grains. A specific attention is to be paid on the two types of granular transport mostly encountered in geophysical and industrial applications, namely granular-fluid flows induced by gravity and/or shearing fluid on top of grains. Contributions should help at improving our knowledge on (i) the coupling mechanisms between grains and the surrounding fluid, and/or (ii) the multiscale modelling of granular-fluid flows for geophysical and industrial purposes.