Breakthrough for one of the “Seven Engineering Wonders of the Modern World”
The Chesapeake Bay Bridge-Tunnel is a 37-km (23-mile) long structure of bridges and tunnels for motor traffic. Near the city of Norfolk and the adjacent naval base in Virginia in the United States, it connects the Hampton Roads region with the Delmarva Peninsula (part of Delaware, Maryland, Virginia). A previous bottleneck is now to be eliminated. At the end of January, a tunnel boring machine (TBM) from Herrenknecht achieved a breakthrough for a tunnel that will contribute to this in the future.
The Chesapeake Bay Bridge Tunnel (officially known as the Lucius J. Kellam Jr. Bridge-Tunnel) has been one of the largest structures of its kind since it opened in 1964. Bridges and tunnels alternate between four artificially raised islands over a length of 37 km (23 miles). Four million vehicles a year pass through the bridge-tunnel in a northerly or southerly direction. Following it opening in 1964, it was named one of the “Seven Engineering Wonders of the Modern World.” In 1965, it was awarded the “Outstanding Civil Engineering Achievement,” by the American Society of Civil Engineers. Since 1999, large sections have been widened from two to four lanes: there is a separate bridge with two lanes for each direction of travel.
The Thimble Shoal Tunnel, which passes under a shipping channel, has been a bottleneck. For a distance of around 2 km (1.2 miles), traffic is reduced to two lanes, one in each direction, to pass through the tunnel. This is set to change from 2028. A major milestone for the expansion has now been reached: the new parallel Thimble Shoal Tunnel has been fully excavated using a TBM. The next step is to line the road in the new tunnel.
TBM “Chessie”
The construction company, a joint venture between Dragados USA and Schiavove Construction Company LLC, relied on a Herrenknecht TBM to build the approximately 2-km (1.2-mile) long tunnel. A so-called Earth Pressure Balance (EPB) shield with a diameter of 13,210 mm, a drive power of 7,000 kW and 46,183 kNm of torque was used. The EPB technology with its earth pressure support is designed for comparatively soft, fine-grained soils and medium earth and water pressures, such as those found when crossing sea floors and rivers at shallow depths. The TBM for the Chesapeake project was given its fitting nickname in a naming competition in the Hampton Roads region: Since then, it has been called “Chessie”.
Special demands were placed on Chessie: it had to be designed to be particularly robust, especially in the area of the excavation tools, in order to minimize the need for compressed air entries as much as possible. One challenge at the start and end of the advance was the low overburden in the area of the man-made islands, where large boulders can also be found.
Joint project success
All in all, Chessie was nine months in charge of tunnelling the almost route. Plus, a delay at the beginning: because near the starting shaft in the area of the first island, an old 3-m (10-ft) high ship’s anchor weighing several tons was stuck in the ground, which first had to be recovered and held up the advance. But the highly experienced joint venture, supported by the Herrenknecht service team, found a solution, cut and removed the anchor directly in front of the cutting wheel, while the TBM was standing in a special seal block construction.
The spoil from the tunnel construction site was loaded onto ships via a belt conveyor from the Herrenknecht subsidiary H+E Logistics and transported away by water. Before the TBM was handed over to the customer for assembly with the support of Herrenknecht Service in the USA, two project managers from Herrenknecht worked on it simultaneously.
“The project was very challenging for us and required a high degree of problem-solving expertise, but together with the customer we overcame all the challenges,” said Michael Kimmeskamp, member of the management board of the Traffic Tunnelling division. “The efficiency achieved as a result and the very positive feedback from the customer show once again: service starts with project management.”
Steffen Dubé, president and general manager of the Herrenknecht subsidiary in the USA, said, “Not every project is the same. With the Chesapeake Bay Bridge Tunnel, we unavoidably had to deal with a high level of complexity. We made up for it through the customer’s trust and an extra level of service.”
On the day of the breakthrough, John Hellman, Project Executive of the joint venture, said in a statement: “Today was a monumental day for the Chesapeake Tunnel JV team, a Dragados and Schiavone joint venture. Our TBM ‘Chessie,’ a Herrenknecht TBM, broke through the headwall to complete the tunnel drive for the Parallel Thimble Shoal Tunnel for the Chesapeake Bay Bridge-Tunnel. This new tunnel will help ensure that commuters traveling between Virginia Beach and coastal eastern Virginia experience less congestion and a safer trip. Thank you and congratulations to everyone who has been a part of this incredible project.”
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