Onset of flow in a horizontally vibrated granular bed: Convection by horizontal shearing

We present experimental observations of the onset of flow for horizontally vibrated 3D granular systems. For accelerations Gamma above Gamma*, the top layers of granular material flow, leading to convection with motion both p arallel and transverse to the shaking; the lower part of the layer moves wi th the shaker in solid body motion. With increasing Gamma, more of the laye r becomes liquefied. The initial bifurcation is backward, but a small amoun t of fluidization by gas flow lifts the hysteresis. A new convective mechan ism, which we explore both experimentally and computationally, associated w ith horizontal shearing at the walls, is identified as the mechanism drivin g the transverse convective flow.