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  2. The World's Largest EPB Shield Tunneling Machine

  • August 2012 Assembly of middle body
  • August 2012 Installation using 3,700-ton floating crane
  • December 2012  World's largest EPB shield tunneling machine fully assembled at Sakai Works

17.45m diameter The World's Largest EPB Shield Tunneling Machine Building an underground highway in Seattle

The Hitachi Zosen Sakai Works has completed work on the world's largest earth pressure balance (EPB) shield tunneling machine, with a diameter of 17.45 meters. The tunneling machine will be delivered by ship to Seattle in March 2013. The shield tunneling machine will be used to dig a highway tunnel for Seattle State Route 99 (SR99), which is to be relocated underground due to aging bridge infrastructure. The 2.8 km tunnel, which begins at the southern end of the Alaskan Way, will be built over a period of about sixteen months starting in Summer 2013.

SR99 tunnel project

Washington State Department of Transportation (WSDOT)
Project title
SR99 Tunnel Project
Seattle Tunnel Partners (joint venture between Dragados USA, Inc. and Tutor Perini Corporation)
Summer 2013
Commence work
Summer 2013

The world’s largest shield tunneling machine was officially named Bertha on December 20, 2012.

A naming competition for the world's largest shield tunneling machine was organized by the Washington State Department of Transportation (WSDOT). The winning name, Bertha, was submitted by a Washington elementary school student.
The naming ceremony was performed at Sakai Works by WSDOT representative Ms. Linea Laird on December 20, in conjunction with the completion ceremony.

Senior officials from the Washington State Department of Transportation

Completed SR99 tunnel (figure of image)

EPB shield tunneling machine with advanced safety systems

Shield tunneling machine in operation (underground)

Completed world's largest shield tunneling machine (figure of image)

  1. 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.
  2. 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.
  3. Above-ground safety is of paramount importance because the machine will tunnel directly beneath a city. As such, the tunneling machine features a range of safety features.
  4. The tunneling machine has been split into sections weighing as close as possible to 900 tons, the maximum allowed under local weight regulations, in order to minimize the number of sections and speed up the assembly process in Seattle.

Made at Sakai Works

Bending the steel plates, Assembling the cutter drive unit, In-factory assembly
Installation in the dry dock, Screw intake, Installation begins
Attaching the screws, Fabricating the disk cutters, Final installation, completion