March 30, 2015

STP gets ready to lift Bertha's business end

Photo from WSDOT [enlarge]

The lift itself could take more than 16 hours.

Seattle Tunnel Partners is getting ready for a big lift along the Seattle waterfront.

Last week, the contractor rolled the giant red gantry crane over the pit where the broken tunnel machine Bertha rests. Crews spent the weekend connecting rigging and making final preparations to lift the machine's cutterhead and drive unit assembly that weighs 2,000 tons.

The Washington State Department of Transportation says a lot of tests will be run before the big lift. The lift itself could take 16 hours or longer.

The crane is called a modular lift tower and was made by Mammoet USA. The company's website says it was designed to fit the limited space next to the viaduct, and steer its payload within millimeters of a target.

The crane will lift Bertha's front end from the 120-foot-deep pit, then rotate the assembly a quarter-turn and set it on a special repair stand.

Next, the crane will help to disassemble the drive unit, starting with 16 electric drive motors, and then the seals and main bearing.

Mammoet engineers designed the crane in four weeks and used components from Malaysia, Europe and Canada. It can lift more than 2,400 tons by using nearly 7 miles of steel cables.

Earlier this month, STP lifted three front shield pieces so crews could reach the cutterhead/drive unit. It used a crawler crane to remove those pieces, which weighed between 80 and 270 tons.

STP hopes repairs will be finished by late May and tunneling will restart in August. STP's latest schedule has the tunnel opening in fall 2017.

A repair plan dated June 16, 2014, originally had Bertha resuming work late this month.

You can see how the giant gantry crane was put together below.