Moving intruder out of noncohesive and cohesive granular assemblies

This paper numerically provides insights into the uplifting process of a circular plate intruder within cohesive and non-cohesive granular assemblies by using an extensive three-dimensional discrete element method. The circular plate intruder is defined by gluing small monodisperse particles, simulated with three different intruder sizes, embedded at three different depths, and subjected to seven different values of the prescribed uplifting force. The numerical method is employed with the inclusion of the capillary attraction forces between near-neighboring particles in the cohesive case of the granular bed, whereas the frictional elastic contact force law is considered for the dry case. The pullout dynamics of the intruder are characterized by its displacement rate and drag force, as well as the force distribution, the packing fraction, and the connectivity of particles within the frustum formed above the intruder. The analysis shows that the uplift rate of the intruder increases with increasing the prescribed pulling force but decreases with increasing the size and embedment depth of the intruder for both cohesive and non-cohesive granular materials. Remarkably, the drag force acting on the intruder varies in a small range at a small uplifting movement of the intruder, reflecting the plastic deformation of the granular bed as a consequence of particles' rearrangement, this force then fluctuates in a large range that increases with the increasing of intruder movement and the magnitude of the uplift force as a result of existing the dynamic interactions between the intruder and particles at the bottom of the frustum, corresponding to the noise of the drag force. The big noise of drag force may be partially explained due to the decrease in the packing fraction and the contact coordination number of material in the frustum during the uplifting process. More interestingly, the results highlight the different linking dynamics between the intruder and granular assemblies, represented via the dynamic relationship between the drag force and the forces distribution within the frustum.