The expansion of concrete caused by alkali-aggregate reaction (AAR) causes significant deformation at the Mactaquac Generating Station, Keswick Ridge, New Brunswick, Canada. Several technologies are used to monitor the deformation behaviour including strain gauges, crackmeters, borehole extensometers, fibre optic sensors and inverted pendulums. The inverted pendulums provide critical information regarding the overall tilt of the concrete structures. The expenses associated with installing such technology and the relatively short life expectancy (due to the large deformations that takes place either from the phenomenon of AAR or from remedial measures that are used to control the effects of AAR) have led engineers to investigate the potential of using GPS sensors to provide supplementary information about movement of the crest of the dam. Six GPS stations were installed at the Mactaquac Generating Station. Two stations were located at the ends of the Diversion and two more stations were located on the crest of the Main Spillway. Two stations were established as reference stations from which relative positions are calculated. Data from the first several months of installation are presented and analyzed. By comparing the displacement information obtained using GPS with the information obtained from the other sensors, conclusions are drawn from the perspective of assessing GPS as a tool for monitoring deformation in dams. Displacement update frequency, displacement accuracy and the overall contribution of the displacement information to the understanding of the deformation behaviour are considered.
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