Dammsäkerhetsanalys via stabilitetsberäkningar för Långströmmens kraftverk : En jämförelse mellan olika dimensioneringsmetoder

Sammanfattning: A detailed dam safety evaluation (in Sweden called FDU) was performed in 2009 by WSP where stability control was performed for Långströmmen power plant with associated spillways. This evaluation concluded that stability could not be ensured, and risk of sliding occurred. The evaluation is based entirely on the recommendations outlined in RIDAS, the power companies guidelines for dam safety, and it is clear that extensive renovations are necessary to stabilize the dam. In this work, the stability will also be checked with guidance through new proposals on guidelines for concrete dams sliding stability, ELFORSK’s report 08:59. This report considered the guidelines in RIDAS as oversimplified, both from an international perspective, but also with regard to the current state of knowledge regarding dam safety. They also believe that RIDAS gives inconclusive results, since for some dams provide conservative results and for other dams result in the unsafe side. This report should therefore check the effect of calculating stability with use of the two dimension methods to get results that can then be analyzed for discussion regarding the appropriateness of using the new proposals on guidelines provided in ELFORSK. Via the use of ELFORSK requires that most material parameters are decided through further examinations of the rock in situ. These material parameters are then used to determine the shear strength of the interface between concrete and rock in the foundation section of the dam. Where the sliding safety be determined with respect to the contact surface both with and without the influence of adhesion. The results of the calculations through both RIDAS and ELFORSK are presented in the following report. Results are based on the screening of Långströmmen spillways, and one of its monoliths. The results show that for cases where no adhesion counted obtained results that do not meet standards of sliding stability. This also applies to the calculation under RIDAS which also shows results that do not meet standards of sliding stability. In the comparison of methodologies related to the need for tensioning cables to achieve the necessary safety against sliding, thus given results that are directly comparable because methodologies relate to different safety factors. In the event that the adhesion counted achieved results well on the safe side. For use of ELFORSK’s proposed new guidelines, there are no objections to not be able to use these. Whether to include the adhesion of the contact area is seen as risky as this assumes that the adhesion is constant and thus is not lost along the dam’s life. Whereupon this method, including adhesion, is recommended to not be included in the calculation.