The Herrenknecht TBM EPB named “The Mighty Quinn” arrived at its destination in early August after boring a total of 5.64km under the city of Columbus, Ohio, USA. For the Lower Olentangy Tunnel Project, the machine (4.1 m in diameter) completed two drives and an extension 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, the machine was equipped with various 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. First, the machine bored the south tunnel. Upon reaching the target shaft, it was dismantled and brought back to the launch shaft to bore the north tunnel in the opposite direction. 

The new tunnel will help keep the Olentangy River cleaner by providing a safe place to divert the overflow of untreated sewage from the city’s century-old network of underground pipes during heavy rains.

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