EXPERIMENTAL AND NUMERICAL-STUDIES OF SHEAR LAYERS IN GRANULAR SHEAR CELL

The stability of a shear layer inside a granular material in a gravity field is studied experimentally and numerically. A shear cell is buil t of transparent acrylic to visualize the motion of the granular mater ial. This shear cell consists of two concentric cylinders containing l ayers of uniform spheres in the annular space between the cylinders. T he shearing motion of the spheres is produced by rotating the bottom b oundary of the cell. Friction of the cylinder walls resists the shear motion, thus creating a single shear layer adjacent to the bottom boun dary, while the rest of the layers above move with constant speed as a solid body. As the rotation speed of the bottom boundary increases, t wo layers adjacent to the bottom boundary begin to shear. This shearin g zone quickly thickens and dilates as the rotational speed increases. The transition of this shear motion from a single layer to many layer s of shearing is studied by video recording. The initiation of this tr ansition is observed to depend on the material properties and the numb er of layers overlaying the shear layer. A one-dimensional numerical m odel is constructed to bring insight into this transitional phenomenon .