The Herrenknecht EPB shield machine, which has a 4.1m diameter, completed two drives and an extension for the project in Columbus, Ohio.
The alignment was through challenging geology, including sand and gravel, silty sand, cohesionless silt and clay, and a small bedrock section with boulders, cobbles, and water. To tackle these conditions, Herrenknecht equipped the TBM with features including a copy cutter, anti-roll fins, an inflatable emergency seal in the tailskin, and a bentonite lubrication system.
Both drives started from the same launch shaft. After completing the south tunnel, the TBM was dismantled and returned to the launch shaft to bore the north tunnel in the opposite direction.
Logistically, this required the teams to adapt their launch plan to accommodate the figure eight style shaft with launch angles separated by 120 degrees.
Herrenknecht said praised Granite Construction’s “outstanding inventiveness and ingenuity” in mastering the challenge of the umbilicals and the layout of crucial launch machinery.
The new tunnel will help to reduce combined sewer overflows into the lower portion of the Olentangy River.
