For more than three weeks, a machine that runs like a coffee grinder steadily carved a tunnel, 18 feet beneath the riverbed of the Buffalo River.
Its operator, Dermot Dowd, guided the machine during 12-hour days from a small control booth off Ohio Street. The limestone beneath the river proved as tough as expected to break through. But the knives and discs on the machine's cutter head lived up to their billing, too.
And now National Grid has a tunnel that's 6 feet wide and 440 feet long that its power cables will run through, from Ohio Street to Ganson Street.
The tunnel, an $11 million project, will help the utility meet emerging power needs in areas like Ohio Street, the RiverBend area and the Outer Harbor. The project began last fall, but the tunneling started May 1.
"It was a very tricky, very difficult tunnel," said Sean O'Keeffe, a site engineer with Ward & Burke Tunneling. Not only was the rock difficult to penetrate, he said, but the project called for a curved tunnel, with a tight radius, which added to the complexity.
Dowd is back home in Ireland, after guiding the remote-controlled tunnel boring machine to its destination last week. While the job was underway, Dowd tracked the 29-ton machine's progress through video screens and pressure and flow readings from inside the booth, O'Keeffe said. "It takes a lot of concentration."
A video recording captured the moment last Thursday when the machine broke through a wall leading to a shaft on Ganson Street, connecting the two sides of the river. "It was great relief, and it came out on target," O'Keeffe said.
Michael Roberts, senior construction supervisor with National Grid, said Ward & Burke kept the project on schedule. "They said they were going to deliver, and they delivered," he said.
The utility estimated 8,000 tons of soil and limestone were excavated through the project. After the material was removed and treated on site, it is suitable for use in projects like building roads. Roberts said material from the National Grid project will be donated to a developer, rather than put into a landfill.
Completing the steel-reinforced concrete tunnel was an engineering feat, but there's more work to do, Roberts said. Equipment that supported the tunnel boring will be removed, conduits will be added to the tunnel, and power cables will be strung through them. The 53-foot deep shafts on both sides of the river will be refilled and covered with giant manholes. Everything should wrap up in July.
"You'll never even know we were here, once we're done," Roberts said.