Tualatin Interceptor and Siphon Improvements Design Build

• LocationTualatin, Oregon
• Timeline2019
• Construction
  MethodsMicrotunneling
  Design-Build

Scope

Michels Trenchless, Inc. used microtunneling to build a 500' long tunnel approximately 40' under the Tualatin River. The 84" diameter tunnel has a 650' radius U-shaped curve, which required installation of a specialized reinforced concrete pipe specifically engineered to withstand the large jacking loads required to obtain the vertical curve. In addition, the joints were fitted with hydraulic joint controls to allow for the curvature of the pipe.

Inside the 82" RCP casing, the tunnel contained a bundle of three HDPE pipelines 14", 16" and 30" in diameter. The carrier pipes replace the original wastewater siphon and provide service for the municipality.

The 650' u-shaped curve set a North American record for tightest vertical curve microtunnel of 84" diameter. A Herrenknecht AVN 1800 machine with double-steering articulation was used to accommodate the radius of the curve and a telescoping section for advancement of the machine. The project started and ended with a 17-degree down angle at entrance and a 17-degree upslope after curve.