With the eastern suburbs of Columbus, Ohio, rapidly growing, the city needed to increase capacity of the existing sewer line. The project called for 24,000 linear feet of a 10-foot finished inside diameter tunnel, access shafts, hydraulic drop structure, passive air quality control and open-cut sanitary sewers.

The interceptor sewer tunnel will connect residences east of Columbus with the collection system that feeds the Southerly Wastewater Treatment Plant. The project area encompasses the Reynoldsburg-New Albany Road corridor and extends from Blacklick Ridge Boulevard, north to Morse Road.  The extension will provide capacity for future growth within the Blacklick Creek Watershed.

The 4-mile long tunnel was constructed in highly complex glacial and post-glacial soil and rock geology with an earth pressure balance tunnel boring machine (EPB TBM) and lined with precast concrete segments. A particular challenge of this project was the high variability of ground conditions. Although EPB TBMs are typically suitable for soft ground, the Blacklick machine was specially designed to handle shale rock as well.

The segments were designed using steel fibers only for enhanced long-term performance. Corrosion inhibiting admixtures were included for long term concrete protection. The project also included near surface facilities such as odor control and junction chambers

The four shafts along the length of the tunnel vary in depth from 35 to 135 feet. Four drop shafts varying in depth and diameter were constructed as part of the project. The shafts involve both soil and rock excavations. Hydrogeological, geotechnical and geophysical studies were performed to select the best technology for tunnel construction and ensure the TBM is designed to operate in a manner that greatly reduces impacts to surface structures and utilities and nearby wells.

As the tunnel Engineer of Record, AECOM provided planning, design and construction services for the project. We also completed numerous workshops with the client and the community during the design process and during construction. The tunnel construction was completed in 2020.