- The slope of the floor at approximately 30 degrees and crew functionality working at such a steep slope.
- The front wall, floor and thrust block design, which also had an equivalent 30-degree slope.
- The thrust force of the reaction block that could potentially push the non-stable soils and react above ground.
- Crossing a U.S Army Corps of Engineers waterway (the Tualatin River).
January 23, 2019
Michels Corp.’s microtunneling team extended the limits of technology by successfully completing a 470-ft long tunnel with a tight, U-shaped vertical curve under the Tualatin River in Tualatin, Oregon. Michels used its new Herrenknect AVN 1800 Microtunnel Boring Machine (MTBM) and specialty 84-in. OD reinforced concrete pipe (RCP) to complete the tight 650-ft radius curve. The Tualatin Interceptor and Siphon Improvements King City Siphon will replace the original wastewater interceptor which was constructed in 1974 and has reached the end of its useful life. The new siphon – a non-gravity fed utility – was fitted with seismically resilient pipe that is better suited for the corrosive environment within the pipeline. The specialty pipe was designed in and shipped from Malaysia for this project. RELATED: 2018 Trenchless Technology Roundtable: The New Face of Trenchless Technology The tunnel was bored in less than a month, holing through in late November; comprehensive planning took substantially longer. Michels worked on the design-build project with project owner Clean Water Services, general contractor Mortenson, and lead engineer Kennedy Jenks for more than a year to design and complete it. That process included a comprehensive review of Michels’ many trenchless construction options to determine which one had the best potential for success. Ultimately microtunneling was determined to be the best fit. The Tualatin project required the boundary-pushing design to allow the siphon system to meet the required functionality with a minimal construction footprint. Typically, a microtunneling project would be launched and received from watertight, secant pile shafts up to 60 ft deep to allow for a straight alignment or minor horizontal and vertical curves. However, this project used 20-ft-deep sheet piling shafts, resulting in significant cost savings. Michels took on the challenging task by proposing the vertical U-shaped curve alignment, even though a similar project with such a large curve or tight radius had not been previously executed in North America. Michels engaged many industry leaders to complete the project. Jackcontrol AG helped in designing and supplying the RCP jacking pipe and hydraulic joints. Aldea Services assisted in technical design of the tunnel and provided oversight. Herrenknecht consulted on the MTBM capabilities and purchase of a new AVN 1800. A VMT gyro steering control system was configured on the MTBM to ensure tight line and grade tolerances were met. In addition, Michels included Derrick equipment and a big bowl centrifuge in its custom-built separation plant. RELATED: Microtunneling in Brookline, Mass. Line and grade are critical to the success of the siphon project as challenging as this one. After the team was assembled and many design meetings were held, some unique challenges emerged. Among them were: