Fig. 1. Sensing principle of FBG sensor

Fig. 2. FBG pressure sensor fabricated by 3D printing. (a) Process of fabricating FBG pressure sensor by 3D printing; (b) front view of 3D printed model with height of 50%; (c) top view of 3D printed model with height of 50%

Fig. 3. Anisotropic 3D printed material. (a) Microstructure; (b) continuous model

Fig. 4. Calibration test of FBG pressure sensor

Fig. 5. Calibration and stability tests of FBG pressure sensor. (a) Wavelength variation of FBG pressure sensor during calibration test; (b) linear fitting of calibration data; (c) stability test at 1600 kPa

Fig. 6. FBG earth pressure sensors fabricated by 3D printing. (a) Different encapsulating materials; (b) different infilling model sizes; (c) different infilling densities

Fig. 7. Relationship between sensitivity of sensor and infilling density

Fig. 8. Positions of FBG pressure sensors

Fig. 9. Installation and downshifting devices of FBG pressure sensor

Fig. 10. Installation diagram of FBG earth pressure sensor

Fig. 11. Pressure variation of FBG pressure sensor during downshifting. (a) FBG pressure sensor at depth of 8 m; (b) FBG pressure sensor at depth of 12 m

Fig. 12. Pressure monitoring for FBG pressure sensor in engineering site