March 27, 2015

Gantry crane rolls into position over pit

Photo from WSDOT

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

Yesterday, the contractor rolled the giant red gantry crane over the pit where broken tunnel machine Bertha rests. In the next week or two, STP will lift out the machine's cutterhead and drive unit assembly that weighs 2,000 tons.

The Washington State Department of Transportation tweeted that the crane is in position, but there are "still quite a few tests to run before the big lift."

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.

In the last week, 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.