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R.A. Vreugdenhil, G. Gibson, M.R. Jorgensen, A. Brown and P.G. Somerville
For the first time for any region of Australia, a modern site specific seismic hazard assessment has been completed for six major dams, incorporating fault mapping and trenching to assess fault source characterisation and likely slip rates. A combination of modern ground motion attenuation relations appropriate for stable continental regions was used. The work was performed in a probabilistic context, and includes significant advances in Australia for all aspects of seismic hazard evaluation. The study found that for a short recurrence interval, a large earthquake distant from the site may have a greater probability of contributing to a low PGA, than a low magnitude event closer to the site. At longer recurrence intervals, the magnitudes that contribute most to the hazard have dropped significantly below the previous levels of magnitude for several storages. The outcome of this work is an understanding of the likely strength and duration of ground shaking at each of the six dam sites for any design earthquake, and an understanding of the contribution of each source zone to the seismic hazard. Ground motion parameters produced by the study have been used as a reasonable basis for subsequent seismic analysis of embankments, towers and spillway structures.Learn more
J. Matthews, A. Crichton, G. Gibson
Glenmaggie Dam is a 37m high concrete gravity dam, which was constructed from 1919 to 1927. ALearn more
design review, which was carried out in line with ANCOLD Guidelines, (SMEC 1999) indicated that the dam did not meet the ANCOLD Guidelines for earthquake. This was despite the fact that the dam was stabilised in 1989 by the addition of 70 post-tensioned ground anchors. Faced with the possibility of having to perform a major upgrade to the dam, Southern Rural Water opted to undertake a more detailed assessment of the seismic loads and to carry out further analysis of the dam using the time history method. The time history method uses an accelerogram to model the forces acting on the structure throughout the earthquake and takes into account the continually changing direction of these forces. It can also be used to determine the size of any permanent
displacements caused by the earthquake, which can then be compared to the maximum allowable permanent deformation of the dam to determine if they are acceptable. The study was carried out by GHD Pty Ltd and also utilised updated seismic information for the dam site provided by the Seismology Research Centre and a geological assessment of the local faults by the URS Corporation. This paper discusses the methods used to determine the seismic loads; the techniques used in the study and the outcomes and follows the process from a dam owner’s perspective.