Cost: $60 million
The city of Portland is required by an Amended Stipulated Final Order to limit and control combined sewer overflow (CSO) events in the Willamette River. As part of the West Side CSO project, the Balch Consolidation Conduit (BCC), Shafts, and Pipelines Project was designed to convey combined sewer and stormwater flows from Northwest Portland, Oregon, to the Swan Island Pump Station via the Nicolai drop shaft.
McMillen Jacobs Associates provided construction engineering services directly to James W. Fowler Co., the contractor for the Balch consolidation conduit, shafts, and pipelines. These services included design of excavation support for shafts, jacking load and face pressure calculations, dewatering system designs, and risk management.
The project consisted of about 6,700 feet (2 km) of 84-inch ID (2.1 m) reinforced concrete pipeline installed by microtunneling, and six shafts up to 75 feet (23 m) deep. Five of the microtunnel shafts were constructed with the cutter soil mixing method (CSM), an innovative construction technology used under difficult soil conditions and relatively new to the United States.
Microtunneling was completed in five segments, ranging in length from 1,133 to 1,685 feet. Approximately 950 feet of a 54-inch ID reinforced concrete pipeline was also installed by microtunneling.
The alignment is located in a congested industrial area and crosses beneath U.S. Highway 30, NW Nicolai Street, and active railroad tracks. The microtunneling segments and shafts faced difficult ground conditions, including very soft soils, highly abrasive soils, landfill material (some contaminated), mixed face conditions, and high groundwater levels.