Dynamics of digging in wet soil

TL;DR

This paper models the burrowing behavior of Atlantic razor clams in wet soil, showing how body shape and cyclic deformations enable efficient movement through frictional media.

Contribution

It introduces a novel burrowing model inspired by razor clams, demonstrating unidirectional motion in a frictional medium despite reciprocal kinematics.

Findings

Body aspect ratio significantly affects burrowing velocity.

Maximum efficiency occurs at an optimal aspect ratio.

The model achieves net displacement without inertia or non-reciprocal motion.

Abstract

Numerous animals live in, and locomote through, subsea soils. To move in a medium dominated by frictional interactions, many of these animals have adopted unique burrowing strategies. This paper presents a burrowing model inspired by the Atlantic razor clam ({\it Ensis directus}), which uses deformations of its body to cyclically loosen and re-pack the surrounding soil in order to locally manipulate burrowing drag. The model reveals how an anisotropic body -- composed of a cylinder and sphere varying sinusoidally in size and relative displacement -- achieves unidirectional motion through a medium with variable frictional properties. This net displacement is attained even though the body kinematics are reciprocal and inertia of both the model organism and the surrounding medium are negligible. Our results indicate that body aspect ratio has a strong effect on burrowing velocity and efficiency, with a well-defined maximum for given kinematics and soil material properties.