Feasibility Study of Anchored Fiber-Optic Strain-Sensing Arrays for Monitoring Soil Deformation beneath Model Foundation

High-accuracy deformation measurement is an essential part of geotechnical model testing, in which fiber-optic sensors have great potentialities. In this study, a 1-g plane-strain model test was performed to investigate the feasibility of using fiber Bragg grating (FBG) strain-sensing arrays for monitoring soil deformation beneath a strip footing. The FBG array with specially made anchors was designed to enhance the fiber-soil interfacial bond and, hence, to improve the measurement quality. Three arrays were embedded horizontally within the soil to monitor internal linear strains, while digital photography-based particle image velocimetry (PIV) was employed to obtain superficial displacement and strain fields. Test results show that the strains captured by FBGs were comparable with equivalent strains determined via PIV analyses in terms of strain development, which reflected the evolution of soil deformation under incremental loads. Finally, the benefits and drawbacks of anchored FBG arrays for monitoring laboratory-scale models were discussed, with the conclusion being that they are capable of capturing internal strains or a strain profile of soil with low noise and high resolution, but there has to be a trade-off between robustness and sensitivity.