Drag force on cylindrical intruders in granular media: Experimental study of lateral vs axial intrusion and high grain-size polydispersity

We report on experimentally measured drag force experienced by a solid cylinder penetrating a granular bed of glass beads including, specifically, a highly polydisperse sample with grain sizes in the range 1–100μm. We consider both cases of lateral and axial intrusion in which the long axis of the cylinder is held horizontally and vertically, respectively. We explore different regimes of behavior for the drag force as a function of the penetration depth. In lateral intrusion, where the motion is effectively quasi-two-dimensional, we establish quantitative comparisons with existing theoretical predictions across the whole range of depths. In axial intrusion, we observe peculiar undulations in the force-depth profiles in a wide range of intrusion speeds and for different cylinder diameters. We argue that these undulations reflect general shear failure in the highly polydisperse sample and can be understood based on the ultimate bearing capacity theory on a semiquantitative level. [Display omitted] •Drag force is measured on a solid cylinder penetrating a granular bed at low speed.•Lateral (axial) intrusion is studied using horizontally (vertically) fixed cylinder.•Lateral intrusion: Data validate theoretical models at all penetration depths.•Axial intrusion: High grain polydispersity causes undulations in force-depth curves.•Force undulations are linked with ultimate bearing capacity of polydisperse sample.