Seattle tunnel, among world's biggest, takes step toward completion

SEATTLE (Reuters) - 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 of Highway 99, an elevated roadway along a densely populated waterfront, will be rerouted to run beneath the city of 650,000 people.

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Workers make preparations to lift the cutting head from Bertha, the world's largest tunnel-boring machine, and lift it out for repairs in Seattle, Washington March 9, 2015. Bertha stopped working in December 2013 after digging just 10 percent of a planned tunnel to replace an aging waterfront highway, leaving crews scrambling to determine how to rescue and repair the 2,000-ton drill. REUTERS/Jason Redmond (UNITED STATES - Tags: TRANSPORT SCIENCE TECHNOLOGY)
Water from Seattle?s tunnel-drilling machine, Bertha, the world's largest tunnel-boring machine starts breaking through the concrete wall from the bottom creating massive dust in the disassembly pit in Seattle, Washington, U.S., April 4, 2017. REUTERS/Karen Ducey
Workers look on as they lift the machine head from Bertha, the world's largest tunnel-boring machine, from an access pit for repairs in Seattle, Washington March 30, 2015. The cutter head of the world's largest-diameter tunnel-boring machine was being hoisted out of a temporary pit in Seattle on Monday as construction crews work to fix a key component in a long-delayed multibillion-dollar highway replacement project. The machine, nicknamed Bertha, overheated and stopped working in December 2013 after digging just 10 percent of a planned tunnel route to replace an ageing waterfront highway that hugs downtown Seattle, stalling a $3.1 billion roadway overhaul. REUTERS/Jason Redmond TPX IMAGES OF THE DAY
Seattle?s tunnel-drilling machine, Bertha, the world's largest tunnel-boring machine starts breaking through the concrete wall in Seattle, Washington, U.S., April 4, 2017. REUTERS/Karen Ducey
Workers look on as the machine head of Bertha, the world's largest tunnel-boring machine, is lifted from an access pit for repairs in Seattle, Washington March 30, 2015. The cutter head of the world's largest-diameter tunnel-boring machine was being hoisted out of a temporary pit in Seattle on Monday as construction crews work to fix a key component in a long-delayed multibillion-dollar highway replacement project. The machine, nicknamed Bertha, overheated and stopped working in December 2013 after digging just 10 percent of a planned tunnel route to replace an ageing waterfront highway that hugs downtown Seattle, stalling a $3.1 billion roadway overhaul. REUTERS/Jason Redmond
Seattle?s tunnel-drilling machine, Bertha, the world's largest tunnel-boring machine starts breaking through the concrete wall from the bottom creating massive dust in the disassembly pit in Seattle, Washington, U.S., April 4, 2017. REUTERS/Karen Ducey
Seattle?s tunnel-drilling machine, Bertha, the world's largest tunnel-boring machine, starts breaking through the concrete wall from the bottom creating massive dust in the disassembly pit in Seattle, Washington, U.S., April 4, 2017. REUTERS/Karen Ducey
Workers attached to cables make preparations for lifting the cutting head from Bertha, the world's largest tunnel-boring machine, and lift it out for repairs in Seattle, Washington March 9, 2015. Bertha stopped working in December 2013 after digging just 10 percent of a planned tunnel to replace an aging waterfront highway, leaving crews scrambling to determine how to rescue and repair the 2,000-ton drill. REUTERS/Jason Redmond (UNITED STATES - Tags: TRANSPORT SCIENCE TECHNOLOGY)
Seattle?s tunnel-drilling machine, Bertha, the world's largest tunnel-boring machine starts breaking through the concrete wall in Seattle, Washington, U.S., April 4, 2017. REUTERS/Karen Ducey
Photographers wait for Seattle?s tunnel-drilling machine, Bertha, the world's largest tunnel-boring machine, to break through the concrete wall in Seattle, Washington, U.S., April 4, 2017. REUTERS/Karen Ducey
A passer by takes a photo as workers lift the machine head from Bertha, the world's largest tunnel-boring machine, from an access pit for repairs in Seattle, Washington March 30, 2015. The cutter head of the world's largest-diameter tunnel-boring machine was being hoisted out of a temporary pit in Seattle on Monday as construction crews work to fix a key component in a long-delayed multibillion-dollar highway replacement project. The machine, nicknamed Bertha, overheated and stopped working in December 2013 after digging just 10 percent of a planned tunnel route to replace an ageing waterfront highway that hugs downtown Seattle, stalling a $3.1 billion roadway overhaul. REUTERS/Jason Redmond
Seattle?s tunnel-drilling machine, Bertha, the world's largest tunnel-boring machine starts breaking through the concrete wall from the bottom creating massive dust in the disassembly pit in Seattle, Washington, U.S., April 4, 2017. REUTERS/Karen Ducey
Workers look on as they lift the machine head from Bertha, the world's largest tunnel-boring machine, from an access pit for repairs in Seattle, Washington March 30, 2015. The cutter head of the world's largest-diameter tunnel-boring machine was being hoisted out of a temporary pit in Seattle on Monday as construction crews work to fix a key component in a long-delayed multibillion-dollar highway replacement project. The machine, nicknamed Bertha, overheated and stopped working in December 2013 after digging just 10 percent of a planned tunnel route to replace an ageing waterfront highway that hugs downtown Seattle, stalling a $3.1 billion roadway overhaul. REUTERS/Jason Redmond
People gather to watch as the machine head of Bertha, the world's largest tunnel-boring machine, is lifted from an access pit for repairs in Seattle, Washington March 30, 2015. Bertha stopped working in December 2013 after digging just 10 percent of a planned tunnel to replace an aging waterfront highway, leaving crews scrambling to determine how to rescue and repair the 2,000-ton drill. REUTERS/Jason Redmond
Media gather for a press conference near the access pit where the cutting head from Bertha, the world's largest tunnel-boring machine, will be lifted out for repairs in Seattle, Washington March 9, 2015. Bertha stopped working in December 2013 after digging just 10 percent of a planned tunnel to replace an aging waterfront highway, leaving crews scrambling to determine how to rescue and repair the 2,000-ton drill. REUTERS/Jason Redmond (UNITED STATES - Tags: TRANSPORT SCIENCE TECHNOLOGY)
Workers make preparations to lift the cutting head from Bertha, the world's largest tunnel-boring machine, and lift it out for repairs in Seattle, Washington March 9, 2015. Bertha stopped working in December 2013 after digging just 10 percent of a planned tunnel to replace an aging waterfront highway, leaving crews scrambling to determine how to rescue and repair the 2,000-ton drill. REUTERS/Jason Redmond (UNITED STATES - Tags: TRANSPORT SCIENCE TECHNOLOGY)
People look on as the machine head of Bertha, the world's largest tunnel-boring machine, is lifted from an access pit for repairs in Seattle, Washington March 30, 2015. Bertha stopped working in December 2013 after digging just 10 percent of a planned tunnel to replace an aging waterfront highway, leaving crews scrambling to determine how to rescue and repair the 2,000-ton drill. REUTERS/Jason Redmond
Workers look on as the machine head of Bertha, the world's largest tunnel-boring machine, is lifted from an access pit for repairs in Seattle, Washington March 30, 2015. Bertha stopped working in December 2013 after digging just 10 percent of a planned tunnel to replace an aging waterfront highway, leaving crews scrambling to determine how to rescue and repair the 2,000-ton drill. REUTERS/Jason Redmond
A worker monitors cable pulley wheels as the machine head from Bertha, the world's largest tunnel-boring machine, is lifted from an access pit for repairs in Seattle, Washington March 30, 2015. Bertha stopped working in December 2013 after digging just 10 percent of a planned tunnel to replace an aging waterfront highway, leaving crews scrambling to determine how to rescue and repair the 2,000-ton drill. REUTERS/Jason Redmond
Chris Dixon (R), manager of the Seattle Tunnel Project, speaks to the media as Matt Preedy, Deputy Program Administrator at Washington State Department of Transportation (WSDOT), looks on near the access pit where the cutting head from Bertha will be lifted out for repairs in Seattle, Washington March 9, 2015. Bertha, the world's largest tunnel-boring machine, stopped working in December 2013 after digging just 10 percent of a planned tunnel to replace an aging waterfront highway, leaving crews scrambling to determine how to rescue and repair the 2,000-ton drill. REUTERS/Jason Redmond (UNITED STATES - Tags: TRANSPORT SCIENCE TECHNOLOGY)
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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.

"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.

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 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 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 access pit to make repairs.

(Editing by Lisa Von Ahn and Bill Rigby)

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