Design and Calibration of a Fiber-Optic Monitoring System for the Determination of Segment Joint Movements Inside a Hydro Power Dam

In hydro power dams with arch dams as water storage, the movements of the concrete segment joints are monitored. New monitoring concepts are required as most dams were updated to more efficient pumped-storage power stations within the last years, which significantly changed the loading conditions. Inside one specific dam, the largest segment joint movements were up to 2.5 mm in the past. We developed a fiber Bragg grating (FBG)-based automatic monitoring system for the simultaneous measurement of concrete segment joints. Using our fiber-optic calibration facility, several commercial FBG-based strain transducers were tested. The facility and its capabilities are described. For the investigated sensors, nonlinearity and hysteresis effects of more than 20 μm/m were found, which is much more than expected. The results clearly show the need for standards in fiber-optic sensing where minimum requirements for sensor specifications should be defined. In an extended field trial, several appropriate sensors were installed in a hydro power dam. First results show an increased number of load cycles and smaller movements for the dam in pumping mode. With the new system, these small deformations can be detected, and it will be investigated in future how they contribute to the aging of the structure.