Monitoring the Alaskan Way Viaduct: A Comprehensive Risk Management Solution
After sustaining earthquake damage, Seattle’s iconic Alaskan Way Viaduct was replaced by the State Route 99 Tunnel. To ensure safe execution of this monumental project, a comprehensive monitoring system was installed to oversee the entire 3.2-kilometer tunnel beneath the city center. Four years later, an additional monitoring system was implemented to manage the safe demolition of the old viaduct.
The History and Legacy of the Alaskan Way Viaduct
Originally completed on April 4, 1953, the Alaskan Way Viaduct was an elevated double-deck structure carrying State Route 99 above Seattle’s waterfront at Elliott Bay and through its industrial hub. Although the 2001 Nisqually earthquake caused minor damage, subsequent inspections prompted state and federal authorities to replace much of the viaduct with an underground tunnel beneath the city’s heart.
The construction of the State Route 99 Tunnel commenced in 2013 with the world’s largest tunnel boring machine, boasting a diameter of 17.5 meters. This engineering marvel required an equally advanced risk management and mitigation system to ensure the safety of existing buildings, engineered structures, and utility networks in Seattle’s highly urbanized environment.
Innovative Monitoring Solutions for Complex Challenges
The project demanded an extensive array of monitoring solutions, tailored to manage structural and geotechnical risks effectively. These solutions included:
- 37 Cyclops (automated total monitoring stations) positioned on roofs and walls of nearby buildings.
- Internal geotechnical instrumentation and underground measurement tools.
- Real-time monitoring managed directly from the tunnel boring machine (TBM) control room.
- Satellite radar interferometry measurements.
All collected data were centralized through the Geoscope decision-support platform, ensuring quick and efficient conversion of data into actionable insights for project stakeholders. This monitoring program is regarded as the most comprehensive ever implemented in the United States.
Sixense: Delivering Expertise in Monitoring the Alaskan Way Viaduct
As a vital member of the Alaskan Way Bored Tunnel team, Sixense provided exceptional technical support and innovative solutions for the project’s unique challenges. Their cutting-edge systems played a critical role in the successful risk mitigation throughout both the tunneling and viaduct demolition phases.
David Sowers, Deputy Program Director at WSDOT (Washington State Department of Transportation), praised Sixense for their unwavering commitment to safety, stating:
“As an important member of the Alaskan Way Bored Tunnel team, Sixense has provided outstanding technical support, delivered innovative solutions to complex challenges, and maintained an unwavering positive attitude.”
