Comparison of Mitigation Alternatives for Water Distribution Pipelines Installed in Liquefiable Soils

Ballantyne, Donald and William Heubach (2003); "Comparison of Mitigation Alternatives for Water Distribution Pipelines Installed in Liquefiable Soils;" Advancing Mitigation Technologies and Disaster Response for Lifeline Systems, Proceedings of the Sixth US Conference and Workshop on Lifeline Earthquake Engineering, James Beavers, Editor, August.

Water pipeline distribution system mitigation measures are being evaluated: pipeline replacement, automated pipeline control systems, and planned manual valve actuation response. Seattle Public Utility's distribution system is being used as model for this evaluation. The most vulnerable part of the distribution system is located in the highly liquefiable Duwamish River Valley. A decade ago, it was estimated that it would cost in excess of one billion dollars to replace all of the cast iron pipe founded in liquefiable soils in Seattle's system. This cost was too expensive particularly when considering the other financial demands confronting the utility such as water treatment and reservoir upgrades. Seattle has joined forces with other water utilities in seismically active parts of the world to fund research under the American Water Works Association Research Foundation to evaluate alternate, less expensive, means of mitigating pipeline damage to improve the post-earthquake functionality of the system. The concern is that many pipelines will break, draining water from storage reservoirs, and also affect areas without significant pipeline damage. Following the Kobe earthquake, as well as many other earthquakes, this scenario has resulted in loss of water for fire suppression. Damage in the 2001 Nisqually Earthquake, as well as similar events in 1965 and 1949 was limited to less than 40 failures. However, a Cascadia subduction or Seattle Fault event will be much more damaging, and Seattle wants to be ready. The general strategy is to quickly isolate the damaged sections of the distribution network, or to replace pipe in the network so it will not fail. For each of these options, scenarios are being developed estimating pipeline performance and the resulting network hydraulic performance. The estimated costs and expected losses are being developed for a range of mitigation options.
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