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Saturday, 21 Oct 2017

Strain measurements in embankment dams

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There is growing interest to measure strain in many civil structures such as dams, bridges and tunnels. Optical fibre sensors are increasingly used to measure both temperature and strain in such constructions. Essential development of this application for dams has been made by Sensornet and HydroResearch within various research projects funded by Elforsk AB. The information below is taken from the research report DTSS4.

The applied strain sensing technology allows a full coverage of an entire dam. Local movements can be detected at an early stage if the movements of the dam effectively are transferred into a cable. With strain measurements we can are now able to detect areas of movements in the dam. Altough strain measurement is still under development and more research is needed it is already a reliable method to use either as Early-Warning-System with continuous monitoring, or as an investigation tool to measure movements regularly.

At the Swedish dam Suorva "East" measurements were done within a research projcect between September 2005 and May 2007. The following strain measurements were provided with Sensornet DTSS-system:

The above figure shows the results of the strain measurements in Suorva “East”. They demonstrate a reasonable symmetry about the turnaround point. Although the trace appears noisy, most features are suitably wide, indicating that they are not a feature of measurement error, but genuine physical features. Having made this point it is important to note several positions of high compression on the cable, possibly due to a high local load on the cable. The figure shows three traces, but the repeatability of the strain measurement is so good that it is difficult to make out any variation in the figure above.

Other than Suorva we are now doing regular strain measurements at Ajaure, Grytfors, Hällby, Näs and Seitevare on behalf of the dam owners.