Crews continue to prepare for the arrival of the HRBT Expansion Project ‘s TBM and are working on expanding the existing North and South islands to accommodate the new twin tunnels. Additionally, crews are assembling to begin work to widen the interstate in Norfolk and Hampton.
On the South Island in addition to the excavation of the launch pit and tunnel approaches, a quay dock is being constructed to receive the TBM and the structural integrity of the soil is being tested and mixed in other elements as needed in order to hold the weight of the TBM and ultimately facilitate the tunnel boring process.
Crews have been using three hydromill excavators and a slurry processing plant to form walls for a 20 m (65-foot) launching pit. The hydromills have been digging a line of deep, side-by-side rectangular holes to be filled with concrete to form underground walls. These walls will be up to 190 feet deep and will form the outline of a triple-cell cofferdam.
To keep the hole open until the concrete is placed, the hydromills fill each excavation with a thick slurry as they dig. This slurry is pumped out when the concrete arrives and is then filtered and recycled for use in the next hole. When the concrete walls are complete, crews will be able to excavate the space inside the pit.
Recent work on a portion of Willoughby Spit created a laydown area for additional construction equipment, office space and storage area.
With a completion date in November 2025, work will be happening simultaneously for the twin tunnels, new bridges and interstate widening.
The assembly process of the TBM, whose arrival will be in Fall 2021, will take four to six months. The assembled TBM will be over 400-feet long and weigh over 4,000 tons.
The TBM will be launched in early 2022, and will reach the North Island a year later after working at the rate of up to 15 m/50 feet per day. In the following four months the machine will be turned around before starting to dig the parallel tube towards the South Island. Each tunnel will be about 2,400 m (8,000 feet) long and the deepest segments will be about 45.72 m (150 feet) below the water’s surface: about 15.24 m (50 feet) deeper than the existing tunnels. Click here for further on the project, here and us/125 for the tunnelbuilder archive. Visit www.hrbtexpansion.org. 53/20.
