Case Study: QC Failures in Drilled Shaft Foundations on Seattle Waterfront Project (Washington, 2019)

Project Overview
• Name: Seattle Waterfront Redevelopment
• Location: Seattle, Washington
• Year: 2019
• Project Size: $520 million
• Scope: Construction of piers and foundations along waterfront
• Lead Agencies/Contractors: City of Seattle /

Category of the Issue, Problem, or Challenge
• Quality Control
• Geotechnical
• Structural

Summary of the Issue, Problem, or Challenge
Inadequate inspection of drilled shaft concrete placement led to voids and inconsistent shaft integrity, requiring corrective grouting and partial demolition.

Root Cause Analysis

• Insufficient monitoring of concrete tremie placement procedures.
• Lack of real-time testing to detect voids and segregation.
• Incomplete training of inspection personnel on drilled shaft QC requirements.
• Poor communication between field QC staff and contractors.

Impacts Due to the Issue, Problem, or Challenge

• Delay of 4 months for corrective grouting and reinspection.
• Additional costs for remediation and increased testing.
• Potential structural risk if defects were left unaddressed.

Corrective Actions Taken

1. Implemented strict procedures for tremie concrete placement monitoring.
2. Introduced real-time integrity testing such as crosshole sonic logging (CSL).
3. Enhanced training programs for QC inspectors and field staff.
4. Established direct communication protocols for immediate issue escalation.

Lessons Learned

• Drilled shaft QC requires rigorous monitoring during concrete placement.
• Real-time testing enables early defect detection.
• Communication and training are vital to QC effectiveness.

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

• Are concrete placement procedures strictly followed and monitored?
• Is real-time integrity testing used consistently?
• Are inspectors trained specifically for drilled shaft QC?