SR 99 Tunnel – Alaskan Way Viaduct

SR-99 "Bertha" Worlds Largest

Project: Alaskan Way Viaduct Replacement – SR 99 Tunnel

Customer: Seattle Tunnel Partners / Dragados

  • Work Summary:

Ballard was brought in early by Seattle Tunnel Partners (STP) on this world-record setting project (largest diameter). The STP team consulted with our hyperbaric support managers during the bidding process to develop a first-of-its-kind saturation habitat specifically for tunnel work. By being on board early, Ballard ensured that the hyperbaric systems fulfilled the needs of both the owners and the prime contractor while liaising on their behalf with State regulators regarding applicable codes and standards. The Ballard-owned saturation system provided the capability of housing up to 20 workers and their life support crews. Ballard schematic reviews, air consumption calculations, site assessments and a hyperbaric operation manual all aided in helping to create a world class hyperbaric tunnel support operation for STP.

  • Project Notables:
    • Developed project specific hyperbaric saturation operations manual
    • Assisted in acquisition of necessary state variances
    • Evaluation, setup and integration of saturation equipment into TBM systems
    • Provided on call compressed air workers for trimix and saturation interventions
    • Provided contractor training


More information on the Alaskan Way viaduct and seawall replacement program at: