King City Siphon Improvements Microtunneling

Michels Trenchless, Inc. used microtunneling to build a 500-foot-long tunnel approximately 40 feet under the Tualatin River. The 84-inch diameter tunnel has a 650-foot radius U-shaped curve. The reinforced concrete pipe (RCP) tunnel contained a bundle of three HDPE pipelines–14, 16 and 30 inches in diameters. The carrier pipes replace the original wastewater siphon and provide service for the municipality.

The U-shaped curve required a specialized RCP engineered to withstand 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.

The project started with a 17-degree down angle at entrance and ended with a 17-degree up-slope after the curve.