Tunnel Boring Machine Prepared for $360M NH Stormwater Tunnel
Testing and commissioning is underway for TBM to drill a sewer tunnel in Manchester, N.H.
The tunnel boring machine for the Cemetery Brook Drain Tunnel project in Manchester, N.H.was lowered in sections into the launch pit on June 18, where it is undergoing testing and commissioning as the team completes final assembly prior to launch set for August.
Granite Janet, a 281-ton tunnel boring machine, arrived on an oversized truck in a parking lot beside the Queen City Bridge over the Merrimack River in Manchester, N.H., late last month as the $360 million Cemetery Brook Drain Tunnel project team prepares for its launch in August.
Bay Crane Cos. transferred the disassembled TBM from a 139-ft truck and trailer onto a 65-ft self-propelled modular transporter using a 450-ton crane, then transported it over CSX railroad tracks to the launch pit where a 700-ton mobile rough terrain crane lowered it, says Jacob Blunden, project manager for Methuen Obayashi, contractor for the project that launched last year and remains on budget and on schedule.
On June 18, Bay Crane Co. used a 450-ton crane to pick a section of the TBM onto the self-propelled modular transporter that hauled it to the launch pit.
Courtesy of Edward Pietrasz, Parsons
The TBM shipment arrived on time from Germany in early June, but was delayed at its Portsmouth, N.H. port of arrival due to permitting requirements for travel with the heavy oversize load, Blunden says.
The project, which began in 2025, is roughly 25% complete overall and has reached 35% cost completion, including the expensive TBM, says Blunden,
When a manhunt in Manchester following a shooting that left two public workers injured the morning of June 18, the team posted a sheriff by the entrance and work continued, says Ed Pietrasz, resident engineer for Parsons, the project’s construction manager. “I arrived at quarter to six and the cutterhead came in around 10 a.m.,” he says.
At the CBDT project’s slurry treatment plant, bentonite and water are mixed with other additives and transported as a pressurized liquid to the cutterhead to prevent soft ground from collapsing. It pulls out muck and debris and sends fresh slurry back through the plant’s loop system.
Photo by Johanna Knapschaefer for ENR
With TBM assembly still underway, testing and commissioning will take place for the next few weeks before launch. “We are testing certain systems as they are completed,” Pietrasz says. “If something gets assembled and it doesn’t work, we don’t want to discover that when it is 100 yards into the tunnel. We’ll test every single component before they push it into the tunnel.”
Piece by piece, the team is running a myriad of tests, including testing the water to confirm the TBM can hold bentonite slurry for the machine’s operation, testing the slurry centrifuge used for treating sludge and operational equipment, testing pumps and shakers that act like sieves, sifting out rocks and debris during mining, and running electrical tests. “Everything has to be functioning prior to mining,” Pietrasz says.
The TBM will include 16 gantries, which will be attached one at a time due to space constraints at the site near the Merrimack River. The gantries, each having a specific purpose, will support the TBM with slurry pumps, water, compressed air and other equipment, moving 20 to 30 ft over weeks.
Photo by Johanna Knapschaefer for ENR
Coordinating with CSX is another important part of the job at the site, where 80 workers report daily.
“We are mining through their property and with the different materials that go through, they have separate testing parameters to make sure there’s no contamination of the material we’ve mined out from their property,” he says. “That’s why we have to segregate their muck and test for their parameters.”
