Effect of boundary on maximum force between rod and granular

The article reports experiments which show that the maximum static friction force F on the surface of an aluminum rod inserted in the dry granular.We observe that cylinder container diameter can affect apparently the force F as it is small.The results show the key role of the force chain and the boundary condition of the container in the macroscopic properties of granular materials.We also observe that the projected area of rod also affects apparently the force F and polyfits the data.