Embedded Quasi-Distributed Fiber-Optic Sensors for the Long-Term Monitoring of the Grouting Area of Rock Anchors in a Large Gravity Dam

Steel anchors were installed in a gravity-dam, in order to increase the stability of the dam. Quasi-distributed fiber-optic strain sensors are centrally positioned in the complete length of these anchors to detect the long-term behavior of the tendon bonded to the rock foundation. Because the sensor rod containing the measuring lengths is directly bonded to the grout in the fixed anchor length area, it is able to measure the longitudinal strain distribution in the anchor bond area. Such sensors help to evaluate the bonding of the fixed anchor bond length in a rock or in difficult ground areas.

Design of the anchors, manufacturing and on-site installations are described. The measuring principle and its characteristics are also described. Measured results given show the ability of sensorequipped anchors to monitor the tendon bond behavior over a period of years. Results four years after sensor system installation are presented.