First U220 breakthrough3 April 2012
Breakthrough was reached on the first bore of the U220 University Link Light Rail in Washington, D.C., US.
The 6.4m Herrenknecht machine completed the 3.2km drive on 21 March with a 3mm inaccuracy. Soft ground along the alignment comprised glacial soils. Contractor was the JV of Traylor Brothers and Frontier Kemper. Jacobs Associates provided design project management and geotechnical engineering. A second Herrenknecht TBM will break through this month on a twin drive for the USD 2bn project. A Hitachi Zosen machine was still approximately three quarters of the way through its 1.85km drive between Capitol Hill Station and Pine Street Stub Tunnel. The TBMs were named Togo and Balto after sled dogs that helped transport medicine during a disease outbreak 90 years ago.