Applications of Fiber Optic Bragg Grating Sensing Technology in a Forked Tunnel Model

Optical fiber Bragg gratings-based strain sensor modules were designed, fabricated, and embedded in a three-dimensional geo-mechanical model of a forked tunnel. These sensors recorded in-situ the strains of the embedded pots in the process of digging the tunnel. These results were compared with those of conventional strain gauges and of predictions from a detailed numerical analysis. The results indicate that the three sets of data (from the fiber Bragg grating strain sensors, the strain gauges and the numerical simulation) follow essentially the same trends and are basically consistent with one another. However, the fiber Bragg grating strain sensors recorded data that are much closer to those predicted with an accurate numerical model, compared with data recorded by the conventional strain gauges. The present experiment provided convincing evidence that the fiber Bragg grating strain sensors have much higher reliability and are more effective than the traditional strain sensors. As such, they are potentially strong candidates for applications in the long-term structural health monitoring of large-scale geotechnical engineering projects.