Dam Monitoring Using Long SOFO Sensor

The SOFO system is based on low-coherence interferometry in single-mode optical fibres and allows the measurement of deformations in civil structures with a resolution of a few micrometers and an excellent long-term stability. SOFO allows permanent, automatic and reliable monitoring and has been successfully tested in different types of structures such as bridges, tunnels and geostructures in Switzerland, Europe and North America. The gage length of the standard SOFO sensors varies between 200 mm and 10 m. Monitoring of the large structures, such as dams or tunnels, requires however the use of sensors with a base length of several tenths of meters. To create such a sensor, certain modifications of the existing (standard) sensor are required. Two long sensors with gage lengths of 30 m and 39 m were designed, assembled and installed in the Emosson dam in Switzerland. They are compared with two parallel rod extensometers during more than one year. The results indicate excellent agreement between the two systems and prove the soundness of the long sensor design. 1. The interest of dam monitoring using fibre optic sensors Monitoring is a very important task in appropriate dam management due to the economic, social and environmental significance of hydroelectric structures. It is fundamental in order to guarantee not only the safety of the structure and its users, but also to optimise the exploitation and the maintenance of the dam.