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First pieces of world’s biggest TBM surface for repairs

24 Mar 15 The first three pieces of the world’s biggest tunnel boring machine (TBM) have been lifted out of an access pit in preparation for repairs.

The TBM, Bertha, has been at a standstill for over a year. She is being used in a US$3.1bn (£2bn) project to build a tunnel to replace the Alaskan Way Viaduct in Seattle, USA. An access pit has been built to enable her to be brought to the surface for repair (link opens in new tab).

Contracting JV Seattle Tunnel Partners (STP) has now hoisted the machine's 270t upper body to the surface, followed by the remainder of her exterior shield – the upper right and left sections, both of which weigh less than 100t.

The final lift will bring to the surface Bertha’s massive cutterhead and main drive unit, which weigh a combined 2,000t.Crews will use a modular lift tower to make the lift.       

The repair effort is being led by STP - a joint venture of Dragados USA and Tutor Perini - and manufacturer Hitachi Zosen.

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