The machine’s cutterhead is 26ft in diameter and is constructing part of a 13.1-mile (21km) network of 23ft diameter tunnels in DC to relieve CSOs.
The TBM is named in honor of Nannie Helen Burroughs, a prominent African-American educator and one of the most distinguished residents of the communities along the Anacostia River. "Nannie" joins "Lady Bird," (DC Water’s first 26ft-diameter TBM used for the Blue Plains Tunnel).
DC Water reports that the TBM cost USD 25M to build, and that the 350ft-long (107m) machine, weighing 1,248t, is expected to average 52 to 64ft per day.
A JV of Impregilo-Healy-Parsons has a USD 254M design-build contract with DC Water for this second portion of the tunnel system, which was awarded in May 2013 and also includes six shafts and three diversion structures needed as part of the system.
