By Martha Bellisle

The Associated Press

SEATTLE — The world’s largest tunnel-boring machine broke through a concrete wall beneath Seattle on Tuesday to reach the end of its long, troubled journey, a milestone in a multibillion-dollar project to replace an aging highway hugging the city’s waterfront.

Critics of the effort to build an underground roadway called it an overpriced endeavor that would collapse under the weight of its ambition and mounting costs. For a while, they looked to be right as the machine, known as Bertha, broke down soon after it started drilling in 2013 and didn’t crank up again until last year.

Bertha has finally capped its 1.75-mile journey, which the state Transportation Department and some media live-streamed online. Social media users posted memes about the time it took to reach this moment, when the giant machine cut through the final pieces of concrete in a 5-foot wall, filling the air with dust.

“Today is a major construction milestone in our plan to reclaim Seattle’s waterfront,” Mayor Ed Murray said. “We will build a waterfront for pedestrians, transit and sensible car trips without a freeway wall casting a shadow over our vision of a well-connected 21st century city.”

Crews will break down Bertha as others prepare the inside of the tunnel to handle double-decker lanes of an underground highway that will replace the Alaskan Way Viaduct, which was damaged in a 2001 earthquake. The $3.1 billion tunnel is set to open in 2019, four years behind schedule. The original completion date was in 2015.

Proponents say the viaduct will no longer wall off Puget Sound. Some conservative lawmakers slammed the project as an expensive vanity project, and environmentalists objected to building another highway in Seattle.

“This is a historic moment in our state’s transportation history,” said Gov. Jay Inslee, adding that it was a time “to reflect on the incredible level of innovation and skill needed to get to this point.”

Republican state Sen. Michael Baumgartner of Spokane, a member of the Transportation Committee, called the project “a tragedy of errors.”

“Only in bonkers, leftist Seattle would an absurdly stupid project that’s massively behind schedule and over cost, would finishing be considered a success,” he told The Associated Press.

Bertha had only drilled about 1,000 feet of its 9,270-foot trek when it hit a steel pipe and ground to a halt in December 2013. Crews spent much of 2014 digging a pit to reach the machine so it could be pulled out and repaired.

The removal of water near the pit sparked concerns about the ground in the area settling and posing a danger to pipes, buildings and roadways. Some businesses reported cracked walls, and monitors detected ground movement near the pit.

Officials ultimately decided the movement stemmed from activity in the pit and natural causes. After being shut down for more than two years for repairs, Bertha began digging again in 2016.

Officials also expressed concern when a barge carrying excavated soil began to tip and dropped material into the water. The spill posed a hazard to tunnel workers and the public.

The courts will decide who will pay for the hundreds of millions of dollars of cost overruns and delays.

Seattle Tunnel Partners and its insurance companies sued in 2015, claiming the state was at fault for Bertha’s breakdown. The Department of Transportation responded with its own lawsuit, seeking unspecified damages because of the delays caused by the breakdown.

Water cascades from the blades of a massive tunneling machine as it breaks through a 5-foot concrete wall while completing boring for the state Highway 99 route Tuesday under Seattle. (Elaine Thompson/The Associated Press)

A massive tunneling machine breaks through a 5-foot concrete wall as it completes boring for the state Highway 99 route Tuesday under Seattle. (Elaine Thompson/The Associated Press)

Media members look on as dust fills a pit below while a massive tunneling machine nears breaking through a 5-foot concrete wall into the disassembly area for the state Highway 99 route Tuesday under Seattle. (Elaine Thompson/The Associated Press)

A worker pumps his fists as he stands between the cutting blades of a massive tunneling machine Tuesday under Seattle. (Elaine Thompson/The Associated Press)

A pair of workers climbs out between cutting blades near the top of a massive tunneling machine Tuesday under Seattle. (Elaine Thompson/The Associated Press)