Pulling out a compliant beam in granular media: particle-based simulations and experiments under X-ray imaging

Natural and engineered intruders in granular media often have compliant bodies. When coupled with the elastoplastic response of the medium, the intrusion process becomes complex. Here, we study the pull-out problem of a compliant beam in a granular medium using Discrete Element Method simulations, where a compliant beam is represented using the bonded particle method. We also conducted corresponding experiments  in which the kinematics of both the compliant beam and surrounding particles are obtained via X-ray imaging. The total resistive force during pull-out shows an initial linear increase, corresponding to an initial transient regime in the beam’s curvature evolution. We found that the peak and slope of the resistive force in this stage increase nonlinearly with the initial embedment depth, while the peak force also increases with the beam’s bending stiffness. Upon reaching the peak force, a nonlinear decay in resistive force response occurs, which corresponds to a slow evolution of the beam’s curvature as its depth decreases. In this stage, we also observe intermittent fluctuations in the beam’s curvature along with rigid-body rotation, which is related to fluctuations in the local yield stresses in the granular medium.