The new tunnel at the Chesapeake Bay Bridge Tunnel will be created using a massive, million-dollar tunnel-boring machine (TBMs). These machines use a circular plate with disk cutters that rotate to cut through rock, muck or sand as it inches forward slowly. As the machine excavates the tunnel, it also helps to build the walls that will eventually support the tunnel.
France and England used 11 massive TBMs to create the three tubes that make up the 32-mile Channel Tunnel. Also called the Euro Tunnel or Chunnel—it took three years to dig those tunnels.
Dragados USA, which operates in 68 countries, has partnered with Schiavone Construction Co. to construct the tunnel. Dragados has built more than 800 miles of tunnel, 5,200 miles of highway and 1,500 bridges and is currently building a large bored tunnel in Seattle. Schiavone has built several subway lines in New York City.
A large pit will be opened 105 feet below the water on the island nearest Virginia Beach. The boring machine will be shipped to the site and assembled at the bottom of the pit.
The machine’s 41-foot rotating head cuts into the soil, carves it out and hauls it away on a conveyor belt before it’s transferred to trucks. Precast concrete tunnel segments are loaded into the machine and pushed into place. Once one ring of concrete is finished, the machine pushes forward, excavates more soil and adds another ring. When it reaches the other side, the machine will be disassembled and removed. Then crews install the roadway, lighting and mechanical systems.
The TBM used at the Chesapeake Bay Bridge-Tunnel will extract about 50,000 dump trucks worth of soil–tests have confirmed that the spoils will be contaminated by the boring process and must be disposed of in a protected landfill.
The TBM requires the use of foams and other substances common to the oil-drilling industry. They lubricate the cutter head and help the spoils flow more easily. Most of the additives are petroleum based, and are considered hazardous.
Those additives are petroleum-based, leaving the spoils tainted with contaminants considered hazardous to health. Measurement currently tally Total Petroleum Hydrocarbons, which are measured in milligrams per kilogram of soil. Environmental protection regulations kick in when TPH hits 50-plus milligrams.
The CBBT samples – a mix of native ground and boring additives – tested at 75 milligrams of TPH, which is barely over the threshold. In heavily polluted sites, rates can climb into the 10,000 range.
There had been speculation that the Wagner Pit and Webster Cannery might be considered as the spoils site, but as was reported in the Mirror, those sites were deemed ineligible due to concerns TPH could seep into groundwater.
Virginia’s Department of Environmental Quality requires that Petroleum-contaminated soils must go to a landfill equipped with a liner and a leachate collection system. Leachate is liquid generated from rainfall and the natural decomposition of waste that is filtered through the landfill to a leachate collection system. The leachate collection system’s job is to direct the leachate to collection sumps so it can be properly removed from the landfill.
Boring does have advantages for the CBBT: Fewer interruptions to shipping in the channel, less risk of damaging the existing tube nearby. Bored tunnels are the norm in Europe and Asia.
The test results and their ramifications have been “expected from the beginning,” Andres Gonzalez, a project executive with the builder, wrote to The Pilot in an email. He said it doesn’t take much TPH to condemn soil to a landfill, comparing the threshold to “placing a drop of liquid into an Olympic swimming pool.”
The boring machine is scheduled for delivery in October. Arriving in sections, it will weigh 5.5 million pounds when assembled.
In the meantime, preparations are under way on the man-made islands. A launch pit is being dug to lower the machine so it can start eating its way under the Thimble Shoal channel, installing concrete rings in the tunnel as it goes. Crews of 20-25 people will man a control room inside the machine. Operations will go on around the clock.
One year after boring begins, the machine is expected to surface on the other side.