Balch Consolidation Conduit, Shafts, and Pipelines

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 is designed to convey combined sewer and stormwater flows from Northwest Portland, Oregon, to the Swan Island Pump Station via the Nicolai drop shaft.

Jacobs Associates is providing construction engineering services, directly to James W. Fowler Co., the contractor for the Balch consolidation conduit, shafts, and pipelines. These services design of excavation support for shafts, jacking load and face pressure calculations, dewatering system designs, and risk management. 

The project consists 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 are being 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 will be 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 will also be 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 face difficult ground conditions, including very soft soils, highly abrasive soils, landfill material (some contaminated), mixed face conditions, and high groundwater levels.

The project is required to be in place and operational by December 2011, and is slated to cost around $60 million.