The machine before it was dismantled for shipping

The machine before it was dismantled for shipping

Largest tunnelling machine prepares for work

01 May 2013

JUMBO’S MV Fairpartner has discharged at the Port of Seattle the largest tunnel boring machine (TBM) ever made. The tunnel boring machine was built by Hitachi Zosen Corporation and loaded at Osaka, Japan. It consisted of a total of 48 pieces weighing 7,700 tonnes and measuring 31.606 cu m with the heaviest item close to 900 tonnes.

The five-storey-tall $80 million tunnel-boring machine was named ‘Bertha’ after Bertha Knight Landes, Seattle’s first female mayor.

With her 17 m diameter and length of close to a 100 m, she will dig the SR99 tunnel beneath downtown Seattle. The tunnel should be operational in 2015. Bertha is owned by Seattle Tunnel Partners (STP), the Washington State Department of Transportation’s contractor for the project.

The machine pieces are to be lowered into a pit and reassembled.

Pieces of the tunnelling machine being
loaded onto the MV Fairpartner in
Osaka for the journey to Seattle

Hitachi was selected ahead of three other firms based on overall technical requirements, support capabilities, price and schedule. Based in Osaka, Japan, the firm has successfully built more than 1,300 tunnel boring machines, a number of them for large-diameter tunnel projects. They are currently supplying the tunnel boring machines for Sound Transit’s Capitol Hill Station to Pine Street segment and the Bay Tunnel near San Francisco, Calif.

The earth pressure balance (EPB) shield tunnelling machine has advanced safety systems

• The slurry pressure system is designed to work with the variety of different soil types found in Seattle. Safety initiatives include injecting excavated soil with chemicals and using slurry pressure to prevent ground collapse.

• The new design allows cutter disks to be inspected and replaced from within the cutter head. This eliminates supplementary construction processes and allows the work to be completed safely at atmospheric pressure.

• Above-ground safety is of paramount importance because the machine will tunnel directly beneath a city. As such, the tunnelling machine features a range of safety features.

• The tunnelling machine has been split into sections weighing as close as possible to 900 tonnes, the maximum allowed under local weight regulations, in order to minimise the number of sections and speed up the assembly process in Seattle.

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