Direct measurement of shear mobilisation in 3D-printed root analogues using distributed fibre-optic sensing

Root reinforcement can increase soil shear resistance, but the way individual roots deform and mobilise resistance during shearing remains difficult to observe directly. This study presents a controlled analogue methodology that combines scanned resin-based 3D-printed root geometries with distributed fibre-optic sensing to measure root-analogue deformation during direct shear testing. Short-and long-embedment configurations were prepared using the same scanned geometry and two resin formulations with contrasting mechanical properties. The short-embedment analogues produced a modest, predominantly local increase in shear resistance, with similar peak strengths for the stiff and compliant materials. This indicates that material stiffness was not fully mobilised when only a limited embedded length was available below the shear plane. In contrast, the long-embedment analogues showed progressive hardening, with shear resistance continuing to increase over the tested displacement range. Fibre-optic measurements showed that tensile strain was progressively mobilised along the embedded length, and integrated strain analysis linked the shear-strength increment to the accumulated axial elongation of the instrumented branch. These 1 observations indicate that the additional resistance in the long-root configuration was governed primarily by tensile mobilisation of the embedded root length, consistent with the development of a soil-root analogue composite across the shear plane. The proposed approach provides a practical framework for directly investigating deformation and mobilisation mechanisms in controlled root-reinforced soil analogues.