Dismantling begins of Washington DC deep-sewer TBM

10 May 2021

With excavation recently completed on Washington DC’s US$600m Northeast Boundary Tunnel (NEBT) project after three years’ tunnelling, crews have now started to dismantle ‘Chris’, the tunnel boring machine (TBM).

Originally lowered in one piece into the CSO 019 shaft located south of the RFK Stadium, the 7.9m-diameter Herrenknecht EPB TBM has mined 8.2km over three years, primarily through clayey ground. In April 2021, it holed through into a water-filled shaft in the Shaw neighbourhood.

Contractor Lanes Construction (US subsidiary of Webuild Group) is dismantling the cutterhead and middle-shield sections of the machine into 20 pieces. They will be crane-lifted out of the shaft onto flat-bed trucks, a process that is expected to take until June 2021.

As the largest component of the Clean Rivers Project, the Northeast Boundary Tunnel is designed to reduce by 98% the quantity and magnitude of combined sewer overflows (CSOs) polluting the Anacostia River. Running at depths of between 15-49m, the tunnel begins south of RFK Stadium and extends north to Rhode Island Avenue NE and west to 6th Street NW.

Once the NEBT is connected to the Anacostia River Tunnel and the First Street Tunnel, it will form part of a complete gravity CSO collection system reducing flows into the Anacostia River. Flows will be conveyed to the Blue Plains Advanced Wastewater Treatment Plant – the largest plant of its kind in the world – prior to discharge into the river.

In addition to controlling CSOs, the NEBT will reduce the chance of flooding in the areas it serves from around 50% to 7% in any given year. The entire project is scheduled for completion in December 2022.