*DENSE FLOWS OF DRY GRAINS*

**Abstract:** We have studied dense flows of dry grains, using discrete numerical simulations and experiments with model materials.
First of all, controling both pressure P and shear rate g, the simplest geometry (plane shear between rough walls without gravity)
reveal that solid fraction and macroscopic friction depend solely on the non-dimensional parameter g/sqrt(P).
The same dependencies are observed in other geometries (annular shear cell and inclined plane).
Then, controling the shear stress, we have measured the hysteretic jamming transition both in annular shear cells
and down inclined planes, and shown the extreme sensitivity of the dynamic of arrest near the threshold.
We compare those results with the predictions of a model describing the growth of rigid clusters of grains near the threshold.