Bertha (tunnel boring machine)

Bertha (tunnel boring machine)
Dennis Bratland · CC BY-SA 3.0 · source
Name	Bertha
Caption	Bertha during excavation of the Alaskan Way Viaduct replacement tunnel
Manufacturer	Hitachi Zosen Corporation / Japan-based consortium
Type	Tunnel boring machine
Location	Seattle, Washington (state), United States
Diameter	57.5 ft (17.5 m)
Length	326 ft (99 m)
Weight	~6,700 short tons
Began	2013
Ended	2017

Bertha (tunnel boring machine) was a large earth-pressure balance and slurry-shield tunnel boring machine used to construct the Alaskan Way Viaduct replacement tunnel in Seattle. Engineered by a consortium including Hitachi Zosen Corporation and assembled by Seattle Tunnel Partners, Bertha became notable for its record-setting size, prolonged stoppage after mechanical failure, and the subsequent legal, environmental, and political controversies involving Washington State Department of Transportation, contractors, and regulatory agencies. The machine's progress intersected with municipal planning debates involving the City of Seattle, the State of Washington, and federal stakeholders such as the Federal Highway Administration.

Overview

Bertha was commissioned to bore a 2.7-mile tunnel beneath downtown Seattle to replace the earthquake-damaged Alaskan Way Viaduct, a structure linked historically to the 1962 World's Fair and regional infrastructure projects like Interstate 5 expansions. The project was managed by Washington State Department of Transportation in coordination with Seattle Department of Transportation and executed by a private consortium that included Kiewit Corporation, J.F. Shea Company, Traylor Brothers, and Finnegan Henderson Farabow Garrett & Dunner-affiliated legal counsel. Initial planning traced to post-2001 Nisqually earthquake assessments and debates involving figures such as Governor Christine Gregoire and Mayor Mike McGinn. Funding and permitting involved entities including the United States Department of Transportation and the Federal Highway Administration.

Design and Specifications

Bertha's design combined components and expertise from Hitachi Zosen, Herrenknecht AG-style TBM concepts, and custom engineering for the geotechnical profile beneath Puget Sound-influenced soils. Specifications included a cutterhead diameter of 17.5 meters, a length of roughly 99 meters, and a mass of approximately 6,700 short tons—dimensions compared in trade press to machines used on the Channel Tunnel and Gotthard Base Tunnel projects. The cutterhead incorporated discs and mixed-ground cutters intended for glacial till, sand, and silt characteristic of the Seattle Basin and stratigraphy studied by consultants such as GeoEngineers, Inc. and URS Corporation. Hydraulic systems, ventilation, slurry separation, and segment erectors coordinated with precast concrete ring segments supplied by contractors and designed to meet seismic resilience standards influenced by lessons from Northridge earthquake and Kobe earthquake engineering research. Sensors and telemetry linked on-board controls to project offices overseen by technical leads and firms including Parsons Brinckerhoff and Arup Group.

Construction and Operation

Assembly occurred in a launch pit near S Chinatown–International District, Seattle with logistical support from Port of Seattle terminals and coordination with Sound Transit and local freight operators. Bertha began excavation in July 2013, advancing under landmarks such as Pioneer Square, Colman Dock, and proximity to the Smith Tower. Operations required coordination with agencies including Seattle Fire Department and utilities managed by Seattle Public Utilities. Progress was monitored by geotechnical instrumentation, and the operation employed tunnel workers organized by unions such as the Laborers' International Union of North America and Operating Engineers. Bertha's tunnelling advanced ring by ring using precast segments and a tunnel boring technique influenced by methods applied in projects like Boston's Big Dig and New York City's Second Avenue Subway.

Mechanical Failures and Repairs

In December 2013, after encountering a steel pipe and unexpected soil conditions, Bertha experienced overheating of its main bearing and cutterhead drive, halting progress. Investigation and repair plans involved contractors Seattle Tunnel Partners, subcontractors, and equipment suppliers from Japan and Germany, plus inspection by independent experts from firms like Mott MacDonald. A 140-foot access shaft and complex retrieval of the damaged bearing assembly necessitated excavation and dewatering that affected nearby infrastructure including the Alaskan Way Viaduct itself and operations at Colman Dock ferry terminal. Legal disputes arose between Washington State Department of Transportation and Seattle Tunnel Partners over responsibility, cost overruns, and delay claims, invoking contractual mechanisms and arbitration clauses similar to issues seen on projects involving Bechtel and other large constructors. The repair period extended into 2015, with the machine resuming tunnelling and subsequently completing the drive in 2017.

Safety, Environmental, and Legal Issues

Safety oversight drew involvement from the Occupational Safety and Health Administration and local agencies as operations intersected with public safety concerns in downtown Seattle and historic districts such as Pioneer Square National Register Historic District. Environmental reviews and permits implicated the Washington State Department of Ecology, National Environmental Policy Act practitioners, and mitigation plans for groundwater and contaminated soils comparable to remediation approaches used at Love Canal and Superfund sites. Vibrations and settlement effects near landmarks raised monitoring and preservation concerns similar to heritage preservation cases involving Statue of Liberty restoration and Getty Center seismic retrofits. Legal controversy included litigation and negotiations among parties such as Washington State Department of Transportation, Seattle Tunnel Partners, insurers, and municipal plaintiffs, with implications for procurement practices and risk allocation in megaprojects examined in literature by scholars associated with Harvard Kennedy School and Massachusetts Institute of Technology.

Decommissioning and Legacy

Following the completion of the tunnel and surface demolition of the Alaskan Way Viaduct, Bertha's legacy influenced debates on urban transportation policy, megaproject governance, and TBM procurement strategy across agencies including Federal Highway Administration, state departments, and international contractors. The project offered case studies for academic programs at University of Washington, Stanford University, and Columbia University on risk management, and informed industry guidance from organizations like the American Society of Civil Engineers and International Tunnelling and Underground Space Association. Bertha's story contributed to policy discussions in State of Washington legislative sessions and municipal planning in Seattle City Council forums, and remains referenced in comparisons with other major tunnelling endeavors such as Big Dig, Crossrail, and the Gotthard Base Tunnel in analyses by publications like The Seattle Times and industry journals.

Category:Tunnel boring machines Category:Infrastructure in Seattle