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  • 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
  • April 2017 Our 17.45m diameter TBM successfully completed tunneling beneath Seattle.

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

Hitachi Zosen Sakai Works manufactured the world's largest earth pressure balance shield tunneling machine, with a diameter of 17.45 meters. The machine was commissioned by Seattle Tunnel Partners, the design-build contractor constructing a 2.8 kilometer tunnel to replace an elevated highway along Seattle's waterfront. It was named Bertha by Washington State students. Built specifically for the soil conditions in Seattle, Bertha is 99.3 meters long and weighs 7,000 tons, and will mine through 650,000 cubic meters. On July 30, 2013, the machine launched and mined approximately 1,000 feet until it struck a 119-foot long, 8-inch diameter unmarked steel well casing on December 3. After sensors indicated increased temperatures in the machine, mining stopped. The machine moved into a repair access pit in February 2015. After removing the cutterhead, Seattle Tunnel Partners directed Hitachi Zosen to repair damages in the seal system and other areas. Hitachi Zosen has made the resumption of mining a top priority. There are approximately 20-25 Hitachi Zosen personnel on site, working six days a week, day and night. The work is aided and overseen by the company's Technology Development Headquarters and Technical Research Institute in Osaka, Japan. In August 2015, crews successfully reattached the cutterhead in the repair pit. After testing, Bertha will resume mining and successfully complete the State Route 99 project.

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

Our 17.45m diameter TBM successfully completed tunneling beneath Seattle in April 2017

Bertha, the TBM manufactured and supplied by Hitachi Zosen to Seattle Tunnel Partners (STP) for the use of the SR 99 - Alaskan Way Viaduct Replacement Project, has successfully completed boring of the tunnel.

Our 17.45m diameter machine, one of the world's largest diameter machines, bored a nearly 3 km tunnel just beneath the center of downtown Seattle and broke through the wall of the arrival pit at the beginning in April 2017.

We were very proud and pleased that our machine has served for the achievement of this historical and high-profile tunnel project.