Monitoring internal displacements of a model dam using FBG sensing bars

Conventional instrumentation has difficulty to measure displacements inside laboratory-scale physical models. In this paper, an innovative fiber Bragg grating (FBG) sensing bar has been developed to perform high-accuracy and real-time monitoring of internal displacements. According to Euler-Bernoulli beam theory, the strain distribution measured by the quasi-distributed FBG sensors adhered on the bar surface can be used to compute the displacement profile along the sensing bar. The effectiveness of the FBG sensing bar has been verified by calibration tests. In the physical model of the Wudu gravity dam, two FBG sensing bars developed by the authors were installed, together with linear variable displacement transformers (LVDTs) and strain rosettes. The FBG sensing bars successfully captured the variation of internal displacement profiles in the model dam. The monitoring results during the overloading test were presented, based on which the deformation mechanism of the dam-foundation system is explained in details. The displacements measured by the FBG sensing bars are validated by their good agreements with those from LVDTs.