Installation and results from 18 months of operation of the dynamic monitoring system of Baixo Sabor arch dam

Abstract

The Baixo Sabor hydroelectric power plant, located in the northeast of Portugal, includes a reservoir with a storage capacity of 630 million m(3) of water created by a concrete double-curvature arch dam, 123 m high, which was equipped with a vibration based structural health monitoring system. This system involves 20 uniaxial accelerometers, 12 of them radially disposed in a gallery close to the dam crest, and the other 8 radially placed along two other galleries. The accelerometers are connected to a set of digitizers distributed in the three instrumented galleries and synchronized by GPS. This paper presents the main characteristics of the monitoring system and the results obtained during the first 18 months of operation, which include the first filling of the reservoir. These results include in particular the characterization of the accelerations amplitude and the evolution of the dam modal parameters (natural frequencies, modal damping ratios and mode shapes), as well as of the influence of the water level and temperature on the modal parameters. Suitable statistical models are applied to mitigate those effects in order to obtain time series of natural frequencies suitable for detection of structural changes.