Measuring Inclinations in Cabril Dam with an Optoelectronic Sensor

Abstract

A high precision inclinometer was placed at the top gallery of Cabril dam, the highest dam in Portugal (132 m). Cabril dam has been presenting, since the first filling of the reservoir (1953), some horizontal cracks in the central upper zone. The dual axis inclinometer, with a recording measuring rate of 1 Hz, was installed for two days; during the same period a digital thermometer, for recording air temperatures, was placed next to the downstream face of the dam. The dam remained under normal operating conditions: the power generation groups were on or off for periods of variable duration each day. The presented analysis of collected data (inclination measured at a point near the dam crest, in two directions, and air temperature and reservoir level) shows a good correlation between the variations in the inclination with the daily thermal wave and with the changes in the reservoir level. The analysis also shows the reliability of the optoelectronic sensor since it was able to detect the vibration induced by the power groups. The inclination measurements were taken in connection with a test on a fully automated geodetic system for continuous monitoring of displacements in Cabril dam.