Seattle, WA – Bertha, one of the world’s largest tunnel boring machines, emerged north of downtown Seattle on Tuesday shrouded in clouds of dust and chunks of falling concrete, completing the most difficult phase of a plan to build a highway under the heart of the city.
The breakthrough of the cylindrical drilling machine marks a major step in one of the most ambitious American municipal projects in recent years. Once complete, 2 miles (3 km) of Highway 99, an elevated roadway along a densely populated waterfront, will be rerouted to run beneath the city of 650,000 people.
A sinkhole, a two-year delay and a $480 million claim by contractors have challenged the $3.1 billion project since it began in June 2013.
The underground highway, which had initially been slated to cost $2 billion and be completed by the end of 2015, has been widely compared with Boston’s 16-year “Big Dig” tunneling project, which suffered through cost overruns, design flaws, worker fatalities and other problems.
Water pours from the base and a cloud of water vapor and concrete dust forms as a massive tunneling machine nears breaking through a five-foot wide concrete wall into the disassembly pit for the State Route 99 highway, Tuesday, April 4, 2017, under Seattle. After tunneling more than 9,000 feet and building an outer tunnel wall as it moved forward, the boring machine finished digging what will be a two-mile, double-decker traffic tunnel to replace the Alaskan Way viaduct, damaged in an earthquake in 2001.
Water pours from the base and a cloud of water vapor and concrete dust forms as a massive tunneling machine nears breaking through a five-foot wide concrete wall into the disassembly pit for the State Route 99 highway, Tuesday, April 4, 2017, under Seattle. After tunneling more than 9,000 feet and building an outer tunnel wall as it moved forward, the boring machine finished digging what will be a two-mile, double-decker traffic tunnel to replace the Alaskan Way viaduct, damaged in an earthquake in 2001.
“This is a historic moment in our state’s transportation history,” Washington state Governor Jay Inslee said in a statement after the drill’s breakthrough. “There is still more work ahead but this moment is one worth celebrating.”
After emerging into a large open-air pit a few blocks from Seattle’s Queen Anne neighborhood, Bertha will be cut into pieces and hauled away over several months.
The 57-foot (17 m) wide borer made by Japan’s Hitachi Zosen Corp cost $80 million and was the largest in the world when tunneling started in 2013.
As engineers make plans to break down the 6,700-ton (6,100-metric ton) machine, work to fill the tunnel with a double-decker roadway has already begun. State planners hope to have the first car travel through the tunnel in early 2019.
While the project’s $3.1 billion price tag is comparatively small – the Big Dig cost an estimated $22 billion – progress was complicated by plans to dig beneath some of the most tightly packed neighborhoods in downtown Seattle.
Bertha overheated and stalled partway through the project in December 2013, putting completion into doubt. Tunneling was delayed two years as engineers dug a 120-foot (37 m) access pit to make repairs.
A worker finishes placing a banner while standing on a narrow ledge above a concrete wall where a massive tunnel machine is expected to break through the next day as it completes boring for the State Route 99 highway, Monday, April 3, 2017, under Seattle. Bertha, the machine digging a 1.75 mile tunnel under Seattle to replace a waterfront bridge with an underground roadway, is reaching the end of its journey. A worker finishes placing a banner while standing on a narrow ledge above a concrete wall where a massive tunnel machine is expected to break through the next day as it completes boring for the State Route 99 highway, Monday, April 3, 2017, under Seattle. Bertha, the machine digging a 1.75 mile tunnel under Seattle to replace a waterfront bridge with an underground roadway, is reaching the end of its journey. (AP Photo/Elaine Thompson)