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Originally published March 11, 2013 at 9:24 PM | Page modified March 12, 2013 at 6:22 PM

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Highway 99 tunnel: Big buildup for a massive drill

The Sodo launch pit and underground vault are almost ready for Bertha, the huge Highway 99 tunnel machine, to arrive at the end of March.

Seattle Times transportation reporter

Key tunnel dates

March 29: Tunnel boring machine “Bertha” scheduled to arrive at Terminal 46

Summer 2013: Assembly finished, the drill begins its journey from Sodo

Fall 2014: Drill to emerge at South Lake Union

Early 2016: Four-lane toll tunnel scheduled to open to traffic

2016: Demolition of Alaskan Way Viaduct

Washington Department of Transportation

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So just how massive is the Highway 99 tunnel drill, arriving later this month?

See that new red crane, sitting this week next to the stub of the old Alaskan Way Viaduct? It’s there just to erect another crane, three times as strong.

And that crane? It will help build another, a horizontal gantry that will straddle the tunnel-launching pit in Sodo to lower the drill’s 41 pieces, including the 886-ton cutter head.

This is the world’s biggest single-bore drill, 57½ feet across. It embarks this summer below downtown, and is to emerge in fall 2014 in South Lake Union. The $2 billion tunnel is scheduled to open to traffic at the start of 2016, at a yet undetermined toll rate.

But before the digging can start, the drill must get here.

Only four or five ships in the world are capable of transporting objects like these, said Chris Bambridge, tunnel engineer for Hatch Mott MacDonald, serving as the state’s construction-management consultant.

The ship M/V Fairpartner, now at the Hitachi-Zosen works in Osaka, Japan, carries its own cranes, as typical cranes are too small. It will dock around March 29 along Terminal 46, the bow facing north toward the Seattle Great Wheel.

The 41 pieces will be hoisted onto a 96-tire truck, which will shuttle them separately at walking speed across the dock to a staging area. Altogether, the 6,800-ton drill will weigh about the same as 38 jumbo jets when it’s assembled in the pit.

The pit is 100 feet deep where the drill will grind through a concrete wall and proceed toward Pioneer Square. This week, a concrete floor is being poured, to cradle the machine at a downward incline. That pad will thicken to 11 feet where the heavy front end will sit, said Amjad Omar, state quality-verification inspector.

Just past the pit wall, workers are installing concrete lids at street level. The slabs will compress the soil so ground water will not float the tunnel tube up and out of position, said Matt Preedy, deputy project administrator for the state Department of Transportation

“These are projects, all by themselves,” Preedy said of the prep work.

At about Yesler Way, the tunnel path dives under the old Alaskan Way Viaduct to pass the triangular Al Boccalino restaurant and the vacant 619 Western Building, a former warehouse and artists’ colony the state is retrofitting for $20 million. Crossbeams on the viaduct were wrapped in carbon fiber to reinforce them against tunneling vibrations.

A total 1,800 big pilings have been buried in the ground or the pit to form a protective box around the machine as it slowly pushes through weak fill soil in a potential earthquake zone. Soil settling would threaten buildings.

An overhead conveyor belt also is being built. Soil will pass out the rear of the cylindrical drill to the pit, where the conveyor will move it in a U-turn north to about Jackson Street before turning toward the waterfront, where barges will take the soil to a quarry near Port Townsend.

Work continues on an overpass, from Terminal 46 to Edgar Martinez Drive, to serve port trucking.

Commuters won’t face another big change until 2014, when the interim Highway 99 segment alongside the stadiums will be shifted farther west, making for a sharper curve. That move will allow workers to link the Sodo interchange and overpass to the south tunnel entrance.

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com. On Twitter @mikelindblom

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