The letters stand for Tunnel Boring Machine (TBM) and it is the technology to be used to bore new twin tunnels next to the existing Hampton Roads Bridge-Tunnel.
Hampton Roads Connector Partners (HRCP), the project's joint construction venture, earlier this month awarded a contract to Herrenknecht of Germany for construction of the TBM. It will take approximately 14 months to build the 46-feet-high machine, approximately four months to ship it from Germany, and another four-to-five months to assemble the TBM on the HRBT's South Island in a 65-foot pit. The TBM stretches the length of a football field. As you can see from the picture of the TBM's cutterhead (pictured here), the machine is about the height of the HRBT Project Office, which is a four-story building.
The TBM will launch from the South Island (Norfolk side), inch its way at a rate of about 50 feet per day (depending on soil conditions) down to the layer of soil known as the Yorktown layer, approximately 50 feet below the current tunnels. The TBM excavates the tunnels with a circular cross section through the soil.
The HRBT Expansion Project (new twin two-lane tunnels, wider interstate and 28 new or rebuilt bridges) costs $3.8 billion. The price tag for the TBM alone is $101 million which represents construction, shipping and assembly costs.
The existing ten tunnels in Hampton Roads are immersed tubes. Advances in tunnel technology make the bored-tunnel approach desirable for the expansion project. The method has fewer environmental impacts and does not disrupt Navy, marine, or commercial traffic in the busy federal channel.
TBMs are typically given female names before they begin work to bring good luck. A female name is chosen because historically, underground workers looked to Saint Barbara for protection. She is the patron saint for military engineers, miners and others who work underground.
Tunneling is expected to begin in early 2022.
