Case Study: High Water Table Discovered During Excavation on San Francisco Bay Bridge Seismic Retrofit (California, 2015)
Project Overview
• Name: San Francisco Bay Bridge East Span Seismic Retrofit
• Location: San Francisco, California
• Year: 2015
• Project Size: $6.4 billion
• Scope: Foundation and seismic upgrade works involving deep excavations
• Lead Agencies/Contractors: California Department of Transportation (Caltrans) /
Category of the Issue, Problem, or Challenge
• Geotechnical
• Differing Site Conditions
Summary of the Issue, Problem, or Challenge
Unanticipated high groundwater levels during foundation excavation required installation of extensive dewatering systems and redesign of excavation support.
Root Cause Analysis
- Underestimation of groundwater conditions during initial site investigations.
- Incomplete hydrological and hydrogeological studies.
- Lack of contingency plans for high water inflows during deep excavation.
- Insufficient coordination between geotechnical and water management teams.
Impacts Due to the Issue, Problem, or Challenge
- Delay of 7 months due to design and installation of additional dewatering and excavation support systems.
- Increased costs related to pumping equipment, energy consumption, and safety measures.
- Heightened risk of excavation instability and worker safety incidents.
Corrective Actions Taken
- Conducted detailed hydrogeological studies and real-time groundwater monitoring.
- Designed robust dewatering and excavation support systems.
- Improved coordination among geotechnical, construction, and water management teams.
- Updated risk management and contingency plans to include groundwater risks.
Lessons Learned
- Groundwater studies are critical for deep excavations near water bodies.
- Monitoring and contingency planning mitigate water-related risks.
- Cross-disciplinary coordination improves project resilience.
Audit & Prevention: Project Control Questions to Ask on Future Projects to Help Control the Situation
- Are hydrogeological studies comprehensive and up to date?
- Are groundwater risks accounted for in design and planning?
- Is there coordination among relevant teams managing geotechnical and water issues?