Forces on a slowly rotating, rough cylinder in a Couette device containing a dry, frictional powder

In the present work, a fine, dry powder was sheared in a Couette device: i.e., sheared between concentric vertical cylinders. The torque generated on the rough, inner cylinder was measured as this inner wall was rotated. Our experiments provided evidence that, in a column of granular material undergoing continuous shearing, normal and shear stresses increase linearly with depth. In other words, Janssen’s analysis ceases to apply if granular material is continuously sheared.