A High-Precision Extensometer System for Ground Displacement Measurement Using Fiber Bragg Grating

Abstract

The design and performance of an innovative high-precision extensometer system, fabricated inexpensively using 3D printing technology, are discussed in this paper. In the development of the extensometer, an embedded Fiber Bragg Grating (FBG) strain sensor was 3D printed using a thermoplastic polyurethane (TPU) filament, which was used as the primary sensing element of the extensometer system, taking advantage of its excellent flexibility and high sensitivity to variations in localized strain. In the performance assessment carried out, the results obtained during the experimental test and validation have demonstrated that it could be used very effectively to measure strain variations, with an average wavelength responsivity of 0.0158 nm/cm (for displacement) and very high linearity (up to 99&#x0025;). Furthermore, the protection integrated into the sensor systems design makes it well-suited for in-the-field applications, such as monitoring ground displacements which can lead to dangerous slippages of sloped earthworks. In addition, a field testing of the extensometer under simulated conditions has shown that a Fiber Bragg Grating (FBG)-based approach could be applied effectively to the measurement of strain, offering a wavelength responsivity of 0.0012 nm/<inline-formula> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> (for strain-sensitive FBGs) under both dry and wet soil conditions. Moreover, taking advantage of the high (&#x007E;99&#x0025;) linearity, the extensometer is a reliable instrument for use in different underground conditions, creating an easy-to-use ground movement monitoring system which then enables an excellent representation of the displacement profile of the earth to be made.