Completing Washington DC Clean Rivers design 22 Jan 2015

Peter Kenyon, TunnelTalk

Construction procurement for the last of the four tunnels that comprise Washington DC’s US$2.6 billion Clean Rivers Project is expected to begin next year (2016).

8,230m NEBT alignment and major structures locations
8,230m NEBT alignment and major structures locations

“The North East Boundary Tunnel (NEBT) is currently in the design phase, which will continue through to 2016,” Pamela Mooring of DC Water told Tunneltalk. “The first phase of construction is anticipated to start in March 2016 to relocate utilities that conflict with the proposed NEBT structures. Construction of the tunnel and supporting infrastructure is estimated to begin in April 2017 and be complete in 2022.”

The NEBT lot originally included an 823m-long branch tunnel known as the First Street Tunnel, but this section was broken out early for design under an emergency schedule following three major flood events in the summer of 2012 in the Bloomingdale and LeDroit Park neighborhoods of northwest DC. The accelerated schedule requires the First Street Tunnel to be in service by 2016 and the new infrastructure – excavation of which is scheduled to begin by the Skanska/Jay Dee JV in April – will temporarily serve as a storage tunnel prior to its connection with the NEBT Tunnel in 2022. At this point it will become a conveyance tunnel as part of a continuous 21km-long connection to the Blue Plains pumping and treatment station.

The NEBT alignment, designed by the project owner’s engineering consultant Jacobs Associates, runs at depths of between 50-160ft (15-49m), crossing under deep foundations of two Washington Metropolitan Area Transit Authority aerial metro tracks, six CSX/Amtrak tracks, a 16-line Amtrak maintenance facility, and numerous 100-year-old plus water and sewer lines. Just north of the Amtrak yard a 46m deep x 17m diameter ventilation shaft will be constructed at a location approximately half way along the alignment. The shaft will also be used as a safe haven for maintenance of the TBM. At its southernmost end, just to the south of the RFK Stadium, the tunnel will connect with the Anacostia Tunnel.

Table 1. Clean Rivers Project tunnels
Alignment Length x i.d (m) Value (US$m) Contractor(s) Progress to date
Blue Plains 7,193 x 8 330.5 Traylor/Skanska/Jay Dee JV 5,000m (67%)
Anacostia 3,810 x 7 253.9 Impregilo/Healy JV TBM launch: April 2015
First Street 823 x 7 157.0 Skanska/Jay Dee JV TBM arrives: Jan 2015
NEBT 8,230 x 7 500.0* n/a In design

* = DC Water (owner) estimated contract price

Additionally, Amtrak has plans to construct a tunnel from DC’s main Union Station to its maintenance facility in the Ivy City neighborhood, possibly at the same time as NEBT construction is taking place – a situation which will require strong coordination between Amtrak and DC Water’s preliminary design engineer, Jacobs Associates.

DC Water estimates the total construction cost for the NEBT at “more than US$500 million.”

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