A Microstructural View of Burrowing with RoboClam

TL;DR

This paper investigates the microstructural mechanics of RoboClam, a burrowing robot inspired by razor clams, demonstrating how soil fluidization reduces burrowing effort through visualization and theoretical modeling.

Contribution

It introduces a novel visualization technique and provides a predictive model for the failure zone during RoboClam's burrowing process, linking soil properties to burrowing mechanics.

Findings

Soil grains are fluidized during RoboClam contraction.

Failure zone size can be predicted from soil and fluid properties.

Continuum models are valid despite grain size being comparable to RoboClam.

Abstract

RoboClam is a burrowing technology inspired by Ensis directus, the Atlantic razor clam. Atlantic razor clams should only be strong enough to dig a few centimeters into the soil, yet they burrow to over 70 cm. The animal uses a clever trick to achieve this: by contracting its body, it agitates and locally fluidizes the soil, reducing the drag and energetic cost of burrowing. RoboClam technology, which is based on the digging mechanics of razor clams, may be valuable for subsea applications that could benefit from efficient burrowing, such as anchoring, mine detonation, and cable laying. We directly visualize the movement of soil grains during the contraction of RoboClam, using a novel index-matching technique along with particle tracking. We show that the size of the failure zone around contracting RoboClam, can be theoretically predicted from the substrate and pore fluid properties, provided that the timescale of contraction is sufficiently large. We also show that the nonaffine motions of the grains are a small fraction of the motion within the fluidized zone, affirming the relevance of a continuum model for this system, even though the grain size is comparable to the size of RoboClam.