Comparative study on the elongation measurement of a soil nail using optical lower coherence interferometry method and FBG method

Optical fiber sensor has gained popularity for structural monitoring in recent decades. Studies on the monitoring for geotechnical structures with fully-distributed fiber sensors, however, are quite limited. In this study, the fully-distributed Lower Coherence Interferometry (LCI) sensors and quasi-distributed Fiber Bragg Grating (FBG) sensors are applied for measuring the strain distribution of a soil nail as a slender structure during pullout test. First, this paper introduces an innovative calibration method for the LCI system. Second, the paper describes the procedures of fiber instrumentation on soil nail. Third, the measured results by LCI technology and FBG technology are compared to study the strain distribution and friction resistance of soil nail during pullout test. Comparative study from test results indicates the characteristics of strain distribution and resistance contribution for different parts of soil nail. Through this study, the advantages and limitations of two sensing technologies are examined.