The biomechanics of burrowing and boring

Abstract

Burrowers and borers are ecosystem engineers that alter their physical environments through bioturbation, bioirrigation and bioerosion. The mechanisms of moving through solid substrata by burrowing or boring depend on the mechanical properties of the medium and the size and morphology of the organism. For burrowing animals, mud differs mechanically from sand; in mud, sediment grains are suspended in an organic matrix that fails by fracture. Macrofauna extend burrows through this elastic mud by fracture. Sand is granular and non-cohesive, enabling grains to more easily move relative to each other, and macrofaunal burrowers use fluidization or plastic rearrangement of grains. In both sand and mud, peristaltic movements apply normal forces and reduce shear. Excavation and localized grain compaction are mechanisms that plastically deform sediments and are effective in both mud and sand, with bulk excavation being used by larger organisms and localized compaction by smaller organisms. Mechanical boring of hard substrata is an extreme form of excavation in which no compaction of burrow walls occurs and grains are abraded with rigid, hard structures. Chemical boring involves secretion to dissolve or soften generally carbonate substrata. Despite substantial differences in the mechanics of the media, similar burrowing behaviors are effective in mud and sand.

Mechanics and Energetics of Soil Penetration by Earthworms and Plant Roots: Higher Rates Cost More

“…Measurements suggest that maximum pressures exerted by earthworms are in the range of 60 to 230 kPa (Keudel and Schrader, 1999; McKenzie and Dexter, 1988). Furthermore, reliance on muscle fibers facilitate motion, allowing faster actuation that enables penetration rates on the order of 100 to 500 μm s −1 (Dorgan, 2015; Dorgan et al, 2007).…”

“…Although individual biopores formed in soil may appear similar, earthworms and plant roots penetrate soil in a different manner. The respective soil penetration rates by earthworms and plant roots vary by three orders of magnitude; earthworms average rates of 200 μm s −1 relative to elongating root tips at 0.2 μm s −1 (Dorgan, 2015, Gregory, 1987). Additionally, earthworms are limited by the maximal pressure exerted by their hydroskeleton, often in the range of 60 to 230 kPa (McKenzie and Dexter, 1988).…”

Adaptation to life in aeolian sand: how the sandfish lizard, Scincus scincus, prevents sand particles from entering its lungs

“…It moves through the sand in an almost fish-like manner, thus its common name is sandfish. The morphological adaptations of the locomotory apparatus and subsurface locomotion have been described and studied previously (Hartmann, 1989; Baumgartner et al, 2008; Maladen et al, 2009, 2011; Knight, 2012; Sharpe et al, 2013, 2015; Dorgan, 2015). In addition, it has been reported (Baumgartner et al, 2007; Staudt et al, 2011; Rechenberg et al, 2004) that the skin is highly resistant to abrasion and shows low friction with sand.…”

Cockroaches traverse crevices, crawl rapidly in confined spaces, and inspire a soft, legged robot

“…The study of climbing has led to undiscovered templates (11) that define physical interactions through frictional van der Waals adhesion (12,13) and interlocking with claws (14) and spines (5). Burrowing (15,16), sand swimming (17), and locomotion in tunnels (18) have yielded new findings determining the interaction of bodies, appendages, and substrata.…”