Pulling objects out of cohesive granular materials

Initiating the motion of an object embedded in granular materials requires applying a force that exceeds a non-null threshold. This study focuses on how inter-granular adhesion affects this threshold. A series of 2D DEM numerical tests involving vertically pulling out plate-shape objects evidences a general linear scaling between the force threshold and the contact adhesion strength. We found that the slope of this relation is proportional to either the plate width or the plate depth, which ever is the largest. This reflects two regimes of mobility controlled by two distinct failure modes: (i) unsticking the plate from the grains underneath it or (ii) spliting a frustum of grains above the plate, which ever is the strongest.