Case Study: I-90 Floating Bridge Design Inadequacies Lead to Construction Delays (2002)

Project Overview
• Name: I-90 Homer M. Hadley Memorial Bridge Replacement
• Location: Seattle, Washington
• Year: 2002
• Project Size: $1.4 billion
• Scope: Construction of a floating bridge to replace aging highway infrastructure
• Lead Agencies/Contractors: Washington State DOT /

Category of the Issue, Problem, or Challenge
• Design
• Marine & Structural Engineering

Summary of the Issue, Problem, or Challenge
During construction, design inadequacies related to anchoring systems and wave load calculations required redesign and rework of foundation elements, resulting in project delays and increased costs.

Root Cause Analysis

• Initial wave load assessments were underestimated due to limited historical data.
• Design did not fully account for extreme weather conditions and marine environment variability.
• Insufficient peer review of marine engineering calculations.
• Lack of adaptability in design to accommodate evolving environmental data.

Impacts Due to the Issue, Problem, or Challenge
• Construction delays totaling 7 months.
• Cost overruns of $22 million.
• Increased risks related to marine operations and worker safety.

Corrective Actions Taken

1. Conducted comprehensive wave load and marine environment reassessments.
2. Redesigned anchoring systems with enhanced safety margins.
3. Instituted rigorous peer review processes for marine engineering designs.
4. Developed flexible design protocols to incorporate new environmental data.

Lessons Learned

• Environmental data must be comprehensive and continuously updated.
• Designs in marine environments require conservative safety factors.
• Peer reviews improve design robustness in complex conditions.
• Flexibility in design allows adaptation to new information.

Audit & Prevention: Project Control Questions to Ask on Future Projects to Help Control the Situation

• Are environmental and marine load data current and comprehensive?
• Does the design include appropriate safety margins for marine conditions?
• Are engineering designs peer reviewed by marine specialists?
• Is the design process flexible enough to incorporate new data?