Coordinating strain responses between optical sensing fibre and gravel soil

The effective coordination between the optical sensing fibre and soil deformation, known as Deformation Coordination between the optical sensing Fibre and Soil (DCFS), plays a crucial role in monitoring soil deformation using Distributed Fibre Optic Sensing (DFOS). In this study, a custom-built triaxial apparatus was utilized to investigate DCFS in gravel materials, an area that has been underexplored in previous research. Some key factors affecting DCFS were examined, including gravel particle sizes and roughness. Optical Frequency Domain Reflectometry (OFDR) and Particle Imaging Velocimetry (PIV) techniques were integrated into the triaxial test to analyze strain distributions of both the optical fibre and triaxial sample. Results indicate that particle properties significantly influence DCFS. Gravel with rougher surfaces and larger particle sizes achieves higher DCFS, thereby enhancing monitoring accuracy. After undergoing three cycles of loading-unloading, the DCFS exhibited a notable increase, followed by a gradual stabilization thereafter. It can be inferred that a stabilized DCFS may serve as a reliable indicator for deformation of gravel in a long-term monitoring, and this has been confirmed by the field cases presented in this paper. The proposed testing methodology and obtained DCFS coefficients offer valuable insights for DFOS applications in gravel soil deformation monitoring.