Bio-inspired burrowing. (a) Schematic representation of strategies employed by burrowing organisms as a function of depth and grain size (from Dorgan (2015)). (b) Force chain map from DEM simulation of bio-inspired probe during self-burrowing showing mobilisation of tip resistance and anchor reaction (data from Chen et al. (2021)). (c) Comparison of length-to-diameter ratios for self-burrowing obtained from cavity expansion analyses for depths between 5 m and 40 m, showing agreement with dimensions of various clam species (data from Martinez et al. (2020)). (d) Burrowing-out curves of bio-inspired actuator showing the effect of sand relative density (D1, D2 and D3 correspond to different sand relative densities, data from Tao et al. (2019)). (e) Actuation strategies consisting of lateral head movement and body elongation employed by a burrowing soft robot (redrawn from Ortiz et al. (2019))