Seismic analysis and design of rockfill dams in the lower Thjorsa River, Iceland

In order to harness the hydropower potential of the lower part of the Thjorsa River in South Iceland, two hydropower schemes are proposed in the area, one near the Urridafoss rapids and the other near the Nupur hill. Three different types of rockfill dams for the two schemes are studied in this paper. Two of the dam types have a central core, one made of loessoidal soil and the other of asphaltic concrete. The third dam type has a concrete face on its upstream side. The proposed building sites are in a well known earthquake region called the South Iceland Seismic Zone. In June 2000 two major earthquakes of magnitude 6.6 and 6.5 occurred in the near vicinity of the proposed sites with a maximum registered peak ground acceleration of 0.84g. The dam design as addressed in this paper is twofold. Firstly, the generalized method of slices is used to analyse the stability of the dam slopes and to determine how steep they can be. Secondly, the Finite Element method is used to perform dynamic analysis to determine the permanent displacements due to a proposed earthquake loading as well as liquefaction potential. The largest permanent deformations developed during earthquake will be approximately 0.4 m but should not jeopardize the overall safety of the dam, although some local damage could occur. Liquefaction of the core material is not plausible.