The Balch Consolidation Conduit Shafts and Pipelines project (“Balch”) was a key component of the City’s Controlled Sewer Overflow program and required installation of 8,000 feet of 84-inch and 54-inch diameter pipes via microtunneling at depths of 20 to 75 feet to carry sewage and stormwater runoff from the Balch Drainage Basin to the West Side Big Pipe, which collects combined sewage from the west side of the Willamette River for conveyance to the Columbia Boulevard Wastewater Treatment Plant on the east side of the river.
The ground conditions in Portland are renowned for being extremely challenging and this site was no exception. Located in a former landfill, the shafts were constructed thru fragments of glass, brick, wood, wire and sheet metal in addition to the expected cobbles, boulders and soft soils. Miscellaneous obstructions encountered during shaft construction included wagon wheels, hot water heaters and an automobile chassis.
The project included six microtunnel drives of lengths ranging from 1,115 feet to 1,690 feet in length. Five launch and reception shafts were constructed using Cutter Soil Mixing (“CSM”) as an alternative shaft shoring method – a method untested in Oregon or in the types of soils on site. Additionally, this project was the first use in the United States of the CSM panels to support the machine and pipeline and for tunnel break-in / break-out zones.
The City prides itself on promoting historically under-utilized minority, women and emerging small businesses (“MWESB”). At the end of the project, JWF had awarded $16.3 million to MWESB firms, a 448% improvement on the original goal!