Vertical pullout of a non-spherical intruder from a granular medium: From system-wide response to avalanching around the intruder

TL;DR

This work addresses vertical pullout of a plate-like intruder in a granular medium, extending beyond initial failure to reveal the post-failure mechanics. It combines open-choice laboratory experiments with index-matching and 2D polygonal DEM simulations to resolve how the intruder and surrounding grains reorganize, form a conical uplift, and sustain a linear, geometry-driven resistance in the steady state. The key contributions include the identification of three pullout phases, the μ-independent convergence of the uplift geometry and macro-fields after failure, and the depiction of a hopper-like flow with intermittent avalanching around the intruder. The findings have implications for predicting intruder resistance in geotechnical and industrial contexts where non-spherical objects interact with granular media, and they point to a broader universality of post-failure behavior across intruder shapes and conditions, including potential extensions to reduced gravity scenarios.

Abstract

Intruder mechanics in a granular aggregate is a common subject in engineering and geotechnical applications. However, most studies are limited to spherical intruders or small displacement regimes up to the point of failure. In this work we investigate the vertical pullout of a plate-like intruder buried within a granular aggregate well past the point of failure. While we find the maximum resistance force to depend on the material properties, in the post failure regime the resistance force converges onto the same curve for all friction coefficients. Likewise, the effective geometry of the intruder will always develop the same conical shape on top of the plate, independent of the magnitude of friction, that remains unchanged during the pullout process once established. Further, between the intruder and the aggregate a natural hopper flow develops in which material is transported into the void below the intruder by discrete flow events.

Figures (18)

• Figure 1: Pictures of the experiment a) before pullout, b) during pullout. Here, $L=0.04$ m is the width of the plate, $D=0.005$ m its thickness, and $H=0.17$ m its initial embedding depth.
• Figure 2: Experimental curve for the pullout resistance $F_{\mathrm{plate},y}$ vs. displacement $\Delta h$ for the plate pullout with different granular materials. The solid lines show data for an embedding depth $h = 0.12$ m, the dashed lines for $h= 0.17$ m. Quartz-Oil mixture data exists only for $h=0.12$ m.
• Figure 3: Initial configuration of the pullout test. The lateral walls and the bottom plate remain fixed while the plate is slowly pulled out with constant velocity $v_{\mathrm{plate}}$.
• Figure 4: Force-displacement diagram of the plate with different coefficients of friction $\mu$. The dashed lines mark the linear fits in the range $\Delta h =[0.08\ 0.2]$. The grey arrow indicates the variation of the occurrence and magnitude of peak resistance with $\mu$.
• Figure 5: Selection for the timesteps I)-V) for the macroscopic fields at different stages of the pullout ($\mu=0.5$). The grey arrows mark the curvature of $F_{\mathrm{plate}}(\Delta h)$ which is used to separate the pullout into different phases.