Experimental determination of friction coefficient and mobilization force for a laterally confined granular column

The case of a cylindrical container filled with granular material is a basic situation where the presence of the cylindrical wall induces horizontal pressure and hence, shearing forces (caused by friction between the container wall and the granular bed). Under certain circumstances, a finite length of the granular column in a housing cylindrical container can stand in the vertical position unsupported at the bottom end, held only by the frictional forces at the wall. When an axial load is applied at one end of the bed and increased slowly, the whole granular column starts to slide at a critical load value, called herein the mobilization force. Since this scenario is of significant practical interest (e.g. in caissons construction or in the design of silos), the experimental determination of the related parameters is of great importance for the development of suitable simulation models. In this paper, experimental methodologies for in-situ measurement of the mobilization force and the Coulomb’s friction coefficient between the granular material and the wall of the housing cylinder are presented in detail. Practical and convenient experimental set-ups that require only a few pieces of readily available and easily operated test equipment are proposed to measure these parameters. Results from a series of example experiments conducted on a granular alumina bed packed in a rigid plastic cylinder illustrate the performance and validity of the proposed experimental methods.