Geography and time weren’t on the side of Mortenson when it needed to design and build a new siphon to move 22 million gallons of wastewater as part of an upgrade to a 42-year-old water system in Oregon.
Clean Water Services, the water resources management utility in Washington County, Ore., needed to improve capacity on a “just-in-time basis” as growth threatened the viability of the wastewater system. The agency sidestepped a traditional design-bid-build method for a progressive design-build effort on a $34-million Tualatin Interceptor and Siphon Improvements project that includes an 84-in.-dia, vertically curved 470-ft-long microtunnel under the Tualatin River. The 650-ft-radius tunnel sets a North American record for the tightest curve radius at this diameter.