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Saturday, 21 Oct 2017

Ajaure Embankment Dam

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Strain measurements at Ajaure Embankment Dam

In September 2004, the first distributed measurement of strain in an embankment dam was undertaken using the Sensornet DTSS within a research project funded by Elforsk.

The system allows the strain and temperature to be measured simultaneously and independently at all points along the fibre. The measurement was carried out at Vattenfall Vattenkraft’s Ajaure dam in Sweden, where a cable was installed at two levels in the crest as indicated in figure. The aim was to compare the measurements taken during September 2004, at full reservoir level, with measurements to be taken at low reservoir level in May 2005.

 The result of the measurements showed no significant strain difference between the two measurements, indicating no significant localized movement of the dam. These initial measurements demonstrate the potential of distributed strain measurements, which is further described by Johansson and Watley 2005. (http://www.waterpowermagazine.com/story.asp?storycode=2025766). Two more measurements will be performed before June 2006.

Whilst undertaking strain measurement at Ajaure, a series of tests were also performed to demonstrate the ability of the DTSS to determine the size of localized deflection in the dam which could be detected by distributed strain measurements. Similar tests were also repeated in the Sensornet Laboratory. Those tests have demonstrated that a deflection of the dam by just 5mm will be detectable. The current sensitivity of the system is suitable for detecting very small localized changes of the dam structure. However, the sensitivity is set to improve with further development, providing enhanced temperature correction and hence much increased strain accuracy. Distributed optical sensing will be an essential tool for dam monitoring, providing location specific information which has not been available before. The distributed technology provides an excellent complement to conventional inclinometers.