As Mary the tunnel boring machine nears the home stretch of her round-trip beneath Hampton Roads harbor, another TBM has wrapped up its role in expanding another of the region’s historic bridge-tunnel complexes.

Approximately ten miles away, as the seagull flies, the 308-ft-long earth pressure balance machine Chessie mined more than 6,300 ft for the Chesapeake Bay Bridge-Tunnel’s new parallel tube at Thimble Shoal Channel, one of two underwater passages along the 23-mile link between Virginia’s mainland and Eastern Shore, and used by four million travelers each year.

Recognized by the American Society of Civil Engineers as one of the “seven engineering wonders of the modern world” soon after opening in 1964 as a two-lane crossing, the bridge-tunnel’s surface roadways were expanded to four lanes in 1999 with the $250-million addition of parallel bridges. The Chesapeake Bay Bridge Tax District, a tax-exempt political subdivision of the Commonwealth of Virginia that operates as a business entity, has been developing a parallel tunnel at Thimble Shoals for more than a decade to address traffic congestion issues caused by the existing tube’s limited vertical and horizontal clearances, which constrain the passage of oversized vehicles.

The project team is currently installing the tunnel ballast, roller compacted concrete and mechanical/electrical from the tunnel entrance in hopes of completing the project in 2028.
Photo courtesy Chesapeake Bay Bridge-Tunnel or CBBT.

Since beginning construction on what originally was to be a five-year project in 2017, Chesapeake Tunnel Joint Venture (CTJV)—a design-build team comprised of Dragados USA and Schiavone Construction Co., with Hatch Mott MacDonald as lead designer—has encountered numerous challenges, particularly massive granite boulders armoring the existing tunnel’s artificial islands that slowed excavation for the TBM’s launch and receiving pits.

And just three months after beginning her mile-long journey in February 2023, Chessie struck what was later determined to be a large ship’s anchor, manufactured in England at the turn of the 20th century. While the machine’s mechanical and drive systems were undamaged, the need to replace 48 wear plates and 389 of the cutterhead’s 442 tools added nearly another year to the project.

Once restarted early last year, CBBT officials say Chessie’s 43.5-ft-dia. cutterhead averaged 50 feet a day on a route more than 50 feet below the seabed. In total, the TBM removed approximately 500,000 cu yrds of soil and installed nearly 10,000 concrete segments, each weighing 10 tons.

According to CBBT executive director of infrastructure Michael Crist, CTJV has lifted Chessie’s shield and cutterhead from the receiving pit, with removal of the remaining gantries to be complete by the end of May. Tunnel ballast, roller compacted concrete and mechanical/electrical are currently being installed from the tunnel entrance. Project completion is scheduled for 2028.

Because CBBT did not expect the expansion to generate substantial new revenue, the Thimble Shoals parallel tunnel has not had the schedule urgency of other toll projects. Still, Crist’s estimated project cost is nearly $100 million higher than CTJV’s originally announced construction contract award of $757 million. CBBT currently has no plans to expand the Chesapeake Channel Tunnel at the northern end of the complex.

Crist says having two major TBM projects within sight of each other has provided many lessons learned for both teams.

“The owners, engineers and contractors working on the project have shared ideas, equipment and personnel from time to time,” he says.

Ryan Banas, project director for VDOT’s construction manager, HNTB Corp., agrees, adding that the fact that Herrenknecht built both Chessie and Mary has brought worldwide expertise to both projects.

“There’s been great synergy there,” he says.