In Seattle yesterday contractors completed a massive lifting operation to remove the head of a stuck tunnel boring machine, called Bertha, for repairs.
They began pulling Bertha’s 2,000-ton cutterhead and main drive unit out of a specially-dug rescue hole nearly 24 hours earlier, on 30 March, but decided to wait until yesterday morning to set the 17.5-m-diameter unit down.
Bertha, the largest boring machine by diameter in the world, has been stuck under Seattle since December 2013.Â
She had just started digging a two-mile-long transport tunnel when a big steel pipe got caught in her teeth and she seized up.
The new tunnel is the centrepiece of a $3.1bn scheme to replace an old double-deck highway bridge that crosses Seattle’s waterfront.Â
Earlier this year Washington State lawmakers proposed abandoning the project even though it had cost $2bn by that point – see ‘Kill Bertha‘ – but the contractors, Seattle Tunnel Partnership, and the Washington State government, carried on with their plan to dig a hole to pull out Bertha’s head and fix it.
So that’s done now.
Bertha herself reacted calmly to the rescue.
"The lift of my 2,000-ton front end is complete. Up next: Further disassembly, then repairs" – was all she said to her thousands of Twitter followers.
For more interesting facts about Bertha and her sad, difficult life so far, see here.
Photograph: Bertha’s 17.5-m-wide cutterhead is set to rest for repairs after being hauled out of a rescue hole in Seattle (Washington State Department of Transport)