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DC prepares for Anacostia EPBM launch 7 Jan 2015

Peter Kenyon, TunnelTalk

Assembly is under way of the Herrenknecht EPBM that will excavate the 3,800m x 8m o.d. Anacostia River Tunnel, the second major tunnel of Washington DC’s US$2.6 billion Clean Rivers Project.

Anacostia River Tunnel shafts
Fig 1. Anacostia River Tunnel shafts

The Impregilo/Healy/Parsons JV will complete the US$253.9 million design-build construction contract as low bidder for the Anacostia River Tunnel, with Parsons as a full construction partner as well as designer. The project owner is DC Water. Contract award was in May 2013, with Notice to Proceed granted the following month. Substantial completion is scheduled for August 2017.

The tunnel starts at the south shaft near RFK Stadium, traveling south before crossing under the Anacostia River, continuing to a junction at Poplar Point where a connection will be made with the Blue Plains Tunnel (Fig 1), which is currently under construction by the Traylor/Skanska/JayDee JV (TBM Lady Bird).

Following lowering and assembly of the cutterhead and shield in the north launch shaft, the Anacostia River TBM (which was named Nannie at a dedication ceremony last month, December 2014) will initially launch with the first six of a total nine trailing gear gantries.

In this configuration the machine will drive the short distance through to the nearby south shaft (CSO19, Fig 1). The two shafts are already joined underground by an interconnecting tunnel constructed using SEM. Excavated Potomac Clay will be delivered to a muck box at the back of the TBM and lifted out by crane. As the TBM advances forward the remaining gantries will be added. After the entire TBM has exited the launch shaft, the shaft will be fitted with muck-handling equipment and full-scale tunneling operations will begin. Three truckloads will be required for each 1ft of advance, for a total of 72,500 journeys. The excavation and muck removal process will be very similar to that of the ongoing Blue Plains Tunnel project featured in the video below.

Full project scope of the Anacostia TunnelProject includes:

  • 3,800m x 7m i.d. tunnel with bolted/gasketed precast concrete lining
  • Six shafts with various configurations that include hydraulic internal structures, vortex drop facilities, and diversion chambers
  • At CSO-019, two shafts with an interconnecting tunnel constructed by SEM to serve as a TBM launch shaft
  • Diversion chambers with connecting diversion sewers and approach channels at two shaft locations
  • Adit tunnels at three locations to connect the shafts to the tunnel. One of these adits will be constructed using microtunneling methods, while the others will utilize SEM
  • A junction structure with the Blue Plains Tunnel at the Poplar Point shaft, which will also serve as a TBM retrieval shaft
  • Ancillary work, including electrical and M&E installations and partial commissioning.

2015 will be a big year for the Clean Rivers Project. As TBM launch approaches for the Anacostia River Tunnel, factory manufacture is complete of the third Herrenknecht TBM for the Clean Rivers Project. The smaller diameter machine (6.1m) will excavate the fast-tracked 823m-long First Street Tunnel for the Skanska/JayDee JV that was awarded construction in October 2013 for a contract price of US$157 million. The First Street contract was broken out of the larger North East Boundary Tunnels package to enable faster project progress of key elements.

Meanwhile, EPBM excavation of the 7,200m x 7m i.d Blue Plains Tunnel has reached the 66% completion mark, with TBM Lady Bird having recorded progress of 4,975m since launch on 29 July, 2013. Breakthrough is expected later in 2015.

By the time the full project is completed, in 2025, more than 21km of tunnels will have been excavated.

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