A FBG based displacement transducer for small soil deformation measurement

Abstract

A small soil deformation measurement system based on fiber Bragg grating (FBG) has been developed for underground displacement monitoring. This new displacement transducer consists of two anchorage plates for the fixation of displacement sensor in soil, a single FBG sensor for sensing the occurred deformation, and a PolyVinyl Chloride (PVC) tube for the protection of inner FBG sensor. The two anchorage plates were fabricated and fixed on the PVC tube surface by FDM process. Gauge length, maximum measurement displacement, and displacement resolution of the proposed FBG displacement transducer were 90 mm, 0.9 mm, and 0.0747 mm, respectively. Raw material of the anchorage plates was Polylactic Acid (PLA) material. An embankment model was established and installed with multiplexed four FBG displacement transducers for the measurement of internal horizontal displacement in laboratory. Both static load and movable load were applied on the top surface of the embankment model. It is found that maximum error of the four sensors under different static load was less than 6%. The monitored strains of four different FBG displacement transducers under movable load were highly consistent, indicating that the smart FBG based small deformation monitoring system can be used to monitor vehicle flow in future. All monitored displacement values were less than 0.03 mm. Therefore the FBG displacement transducer characterized by high resolution can be used to monitor small displacement occurred underground.