Earthworm-soil Interactions and transparent soil tests on bio-inspired tunnelling processes

The unique geotechnical properties of complex seafloor sediments—namely high water content, high compressibility, and low shear strength—present significant technical challenges for traditional rigid exploration equipment, particularly regarding operational stability and deployment. Recently, earthworms have emerged as a critical biological prototype for the development of deep-sea bionic exploration equipment, owing to their unique flexible burrowing mechanisms. However, current bionic designs are often confined to imitating single morphological features or localized movements. The lack of systematic observation and kinematic analysis of their natural burrowing behaviors has become a key scientific bottleneck restricting the development of high-performance bionic exploration equipment.To address this, a bio-friendly transparent soil was prepared in this study. Combined with Particle Image Velocimetry (PIV), visual observations and quantitative analyses were conducted to investigate the kinematic characteristics of Amynthas aspergillum and the evolutionary patterns of the surrounding soil displacement field during burrowing. Experimental results indicate that the bio-friendly transparent soil effectively supports continuous and periodic burrowing behaviors. The locomotion trajectory exhibits significant fractal characteristics, and the kinematic velocity displays a periodic "peak-valley" fluctuation pattern. During the extension-driven burrowing phase, the radial soil displacement exhibits an "8-shaped" bimodal distribution, and a high linear correlation is observed between the axial advancement coordinate of the