Feasibility Study on the Application of Distributed Optical Fiber Sensing on Bank Toe Protection Structure Measurement in Fluvial Physical Models

Accurately simulating and monitoring flexible mattress deformation in mobile-bed models is a challenge. This study develops a realistic model-scale representation of a flexible mattress and uses distributed optical fiber sensing (DOFS) to achieve precise, real-time deformation measurements. A systematic approach is presented, including the design of a 1:30 scaled mattress with appropriately scaled ballast units, the integration of high-resolution strain sensors, and robust attachment methods. Flexible mattress deformation behavior is characterized under two primary modes: straight tensile elongation and bending deformation. A shear-lag analytical model showed that fully bonded fibers achieved near-unity strain transfer and high accuracy under tensile deformation, while bending tests revealed lower transfer efficiency. Nevertheless, strain responses still qualitatively captured the deformation process, because influencing factors uniformly increased strain. The method was further validated in mobile-bed scour experiments, where the DOFS system successfully detected mattress deformations and identified critical features such as scour hole boundaries. Results confirm that DOFS provides accurate and effective monitoring of flexible mattress behavior in fluvial physical models, offering a new approach for high-resolution assessment of erosion protection structures.