Case Study: SR 99 Tunnel Project – Change Orders from Unanticipated Ground Conditions (2016)
Project Overview
• Name: SR 99 Alaskan Way Viaduct Replacement Tunnel
• Location: Seattle, Washington
• Year: 2016
• Project Size: $3.3 billion
• Scope: Bored tunnel replacement of aging elevated highway
• Lead Agencies/Contractors: Washington State DOT (WSDOT) /
Category of the Issue, Problem, or Challenge
• Contract Change Order
• Differing Site Conditions
Summary of the Issue, Problem, or Challenge
Bertha, the tunnel boring machine (TBM), struck an unexpected steel pipe casing left from a previous geotechnical borehole, causing severe mechanical damage. The repair delay triggered a series of change orders as both contractor and owner disputed responsibility and costs under differing site conditions clauses.
Root Cause Analysis
- Incomplete subsurface utility information provided to contractor
- Contract language on “unforeseen obstructions” was ambiguous
- Delays in resolving scope of repair responsibilities
- Lack of shared risk model for subsurface unknowns
Impacts Due to the Issue, Problem, or Challenge
• 2-year project delay
• $223 million in contractor claims
• Extensive legal disputes and cost-sharing arbitration
Corrective Actions Taken
- Amended contract language to clarify unforeseen condition thresholds
- Enhanced documentation of prior site investigations and installations
- Third-party risk allocator hired for future major tunneling efforts
- Added comprehensive geotechnical baseline reports (GBR) in similar projects
Lessons Learned
- Differing site conditions must be explicitly addressed in contract language
- Complete records of historical site activity must be shared
- TBM projects need detailed baseline and risk sharing documents
- Clear claim resolution pathways reduce change order escalation
Audit & Prevention: Project Control Questions to Ask on Future Projects to Help Control the Situation
- Are differing site condition clauses clear and well-scoped?
- Has all subsurface history been disclosed and verified?
- Is a geotechnical baseline report included in bid documents?
- Are dispute resolution procedures defined for subsurface issues?