FIBRE OPTIC SENSORS FOR LONG-TERM SHM IN CIVIL ENGINEERING APPLICATIONS

This paper shows different fibre optic sensors used for such monitoring tasks in civil and soil engineering for which other methods do not have capability. One example is the monitoring of anchors in difficult soil areas by using FBG sensor arrays. Another example presents fibre optic acoustic emission (AE) sensors embedded in concrete piles. They enable precise assessment of the pile's integrity and bearing capacity especially for dynamic loading. The potential of a fibre optic pH sensor to monitor the pH value of steel-reinforced concrete structures in the range from 9 to 13 with a resolution of about 0.5 pH unit is also shown. Concrete-embeddable pH sensors are installed in soil anchors to fix a sheet piling in the oil harbour of Rostock (North Germany). Finally, we report on development of distributed fibre optic sensors and their integration into geosynthetics as they are commonly used for reinforcement of dykes, dams and unstable or endangered slopes. Using the Brillouin frequency-domain analysis, the system is capable of monitoring the strain along the optical fibres and thereby detecting critical soil displacement in case of extreme flood events or slope slides. The system is designed to monitor soil deformation with a spatial resolution of 5 m over a length in the range of 10 km.