Design and Construction of the Spirit Lake Outlet Tunnel, Mount St. Helens, Washington

by John W. Sager, US Army Corps of Engineers, Portland, OR, USA,
Donald R. Chambers, US Army Corps of Engineers, Portland, OR, USA,



Document Type: Proceeding Paper

Part of: Landslide Dams: Processes, Risk, and Mitigation

Abstract:

In 1982, a governmental task force was formed to evaluate the hazard posed by the blockage of Spirit Lake that resulted from the eruption of Mount St. Helens in May 1980. An analysis was performed to determine a 'safe' elevation at which the lake surface could be permanently maintained without danger of the lake breaching the debris blockage. Four possible alternatives were considered for a permanent solution: a buried conduit; an open channel; a tunnel; and a permanent pumping facility. A straight tunnel extending approximately 8,500 feet from the west side of Spirit Lake, through a rock ridge, to South Coldwater Creek was ultimately selected as the preferred alternative. This paper discussed various aspects of the tunnel design and construction.

Subject Headings: Tunnels | Lakes | Hydraulic design | Construction equipment | Seismic design | Embankment dams | Construction sites | Washington | United States

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