DC Water is improving water quality in Washington, D.C., by replacing aging pipelines. The Oregon Avenue NW Sewer Rehabilitation project was constructed by Bradshaw Construction to replace and improve sewers near Rock Creek Park and Bingham Drive.
Of the project’s 4,300 ft of new 24-in. sewer, 2,700 ft was installed by 60-in. microtunneling through the variable rock conditions at up to 90 ft deep. Work areas were particularly challenging as the project was located between a quiet, residential neighborhood and Rock Creek Park. Access had to be maintained for residents, emergency services and visitors to the national park. To minimize public impact, Bradshaw Construction Corp. reduced the seven designed tunnels to three including a single 1,860-ft drive and a 430-ft S-curve with a 625-ft radius. Both drives were record setting for rock microtunneling in the United States for the longest and the first curved drives, respectively. The collaboration and flexibility of the Oregon Avenue team allowed the project to show how far we can push the push the capabilities of microtunneling.
The location’s site constraints drove a great deal of innovative problem solving on the Oregon Avenue NW Sewer Rehabilitation project. One half of the project was constructed within Rock Creek Park, owned by the National Park Service, thus limiting activities to within the 20-ft wide curb lines on Bingham Drive. To protect the park, further constraints minimized tree clearing for crane and vehicles access and all excavation had to be witnessed by an archeologist to inspect for items of historic interest.
The west side of Rock Creek Park is bordered by Oregon Avenue, within the Chevy Chase and Barnaby Woods neighborhoods of Washington D.C., where the second half of the tunnel would be built. An active residential community had significant concerns about how the project would restrict travel around their homes and the impacts of a construction project like this in their front yards. These conditions led to limited access from which to build a tunnel with the only available staging area at the intersection between the two halves of the job. The three tunnels designed along Oregon Avenue were combined into a single 1,860-ft long tunnel drive using 60-in. diameter steel casing behind a microtunnel boring machine (MTBM), the longest at the time in the United States through rock.
Given the length and soil conditions, special considerations had to be made for every utility used in the tunneling operations. Also, the southbound lane of Oregon Avenue had to remain open for traffic and emergency services, therefore shafts had to be narrow enough to fit in the northbound lane and a narrow strip between the edge of pavement and the Rock Creek boundary. Three elliptical liner plate shafts were used to achieve the depths required, up to 50 ft, and avoid existing utilities that may have been damaged by pile installations.
While most of the Bingham Drive section was to be installed by open cut, access had to be maintained from the same, congested project staging area. The tight curvature of the of the street itself had originally required three short, straight tunnels to navigate it. An S-curve tunnel eliminated these two intermediate shafts that would have severely hampered access to the project site.
The two 625-ft radius curves in opposite directions maintained the tunnel alignment along the Bingham Drive footprint within the National Park Service right of way. It also tested both the 48-in. RCP used as a casing and the MTBM.