First there was a 270-ton lift of Bertha’s upper front body segment. Then came the second piece, the upper left section, weighing less than 100 tons. Two more lifts will come, including the final lift that will bring Bertha’s cutterhead and main drive unit, a combined 2,000-ton weight, to Seattle’s surface for repair. Below is a video of the first lift from the crane operator's perspective.
Youtube video posted by Washington State Dept. of Transportation
As part of the plan to repair North America’s largest tunnel-boring machine stuck under downtown Seattle, crews dug an access pit to reach the front of the 57.5-ft-dia machine. After moving Bertha through the pit’s wall, exposing it to light, crews unbolted the shield, disconnected mechanical and electrical connections and welded on lifting eyes.
The first lift, which took place last week, used a Demag CC-2800 crawler crane capable of lifting 660 tons. The second piece was then taken up closer to the weekend, setting the stage to pull up the right side body section of the machine. This third lift is a pick of 90 tons.
Then comes the big lift, which will use a red modular lift tower crane. Mammoet built the crane to lift up to 2,425 tons specifically for this job. At 116 ft wide, 90 ft long and 105 ft tall, the distance between the towers is 75 ft as it straddles the access pit. The crane legs sit on 48 hydraulic cylinders instead of directly on the track rails.
As the final lifts happen in Seattle, the contractor, Seattle Tunnel Partners, builds a canopy to protect the exposed parts from the Pacific Northwest elements as repairs take place above ground.
Tim Newcomb is Engineering News-Record’s Pacific Northwest contributor. He also writes for Popular Mechanics, Sports Illustrated and more. You can follow him on Twitter at @tdnewcomb or visit his website here.