Review of Trenchless Installations at Willamette Water Supply Program

The Willamette Water Supply Program (WWSP) is a partnership between Tualatin Valley Water District, the city of Hillsboro, and the city of Beaverton to develop the Willamette River at Wilsonville, Oregon, as an additional water supply source. This new system, when operational in 2026, will provide a reliable water supply for the region while also helping water system operators balance supply during times of drought or other supply interruptions, adding resiliency to recover more quickly after a large disaster, natural or man-made. The Willamette Water Supply System will include over 30 miles of water transmission pipelines in both 66- and 48-in. diameter. Twenty-five trenchless installations will be constructed in both urban and rural settings. These installations required evaluation of multiple technologies, development of contract documents, and the careful consideration of contractor proposals. The WWSP utilized a consistent approach to these efforts. This consistency resulted in using multiple technologies including microtunneling, guided auger boring, pipe ramming, and pipejacking. Shaft construction techniques also varied considerably. This paper will highlight the common elements used in planning, design, procurement, and construction of the trenchless installations and the results for the owner. A key finding of these installations is that contractor-based solutions require careful evaluation but can yield significant value for the owner. Expertise is required within the owner’s team to facilitate good decision making throughout the project life. Another key finding is that a standard approach to trenchless installations can be applied without limiting innovation or compromising project goals of safety, quality, and cost effectiveness.