Abstract: In this paper, based on common experimental devices and self-made apparatus, the maximal force required for pulling out an object imbedded in a granular packing is studied to explore the peculiar mechanical behaviors of granular materials. Specifically, with an accurale control of the object's orientation and position, the packing fraction, particle roughness and geometric propertles of the object and container are changed to investigate their respective influences on the maximal force. Based on a modified Janssen model, an expression of maximal pulling force required is derived to understand how packing fraction and particle roughness affects the phenomenological parameters in the model. It is proposed that by further generalizing and developing this experiment, it would be able to help students understand the mechanical behaviors of granular materials as well as the elastoplastic properties of various soft matter systems. 

Key words: granular materials, friction, elastoplasticity, Janssen model