Case Study: Unexpected Soft Clay Layer Causes Bridge Pier Settlement in Louisiana (2016)

Project Overview
• Name: I-10 Mississippi River Bridge Replacement
• Location: Baton Rouge, Louisiana
• Year: 2016
• Project Size: $750 million
• Scope: New River crossing bridge with deep foundations
• Lead Agencies/Contractors: Louisiana DOTD /

Category of the Issue, Problem, or Challenge
• Geotechnical
• Differing Site Conditions

Summary of the Issue, Problem, or Challenge
During pile driving for bridge piers, a previously unidentified soft clay layer caused excessive settlement and delayed foundation work.

Root Cause Analysis

• Initial soil borings missed thin but compressible clay lenses.
• Insufficient in-situ testing (CPT and vane shear tests) to detect weak layers.
• Design did not account for potential consolidation settlement from soft soils.

Impacts Due to the Issue, Problem, or Challenge

• Foundation work delayed by 3 months for soil stabilization.
• Increased costs for pile redesign and additional ground improvement.
• Risk of long-term differential settlement requiring monitoring.

Corrective Actions Taken

1. Conducted supplemental geotechnical investigations with CPT and shear tests.
2. Installed deep soil mixing columns for ground improvement.
3. Redesigned pile lengths and diameters based on improved soil profiles.
4. Implemented long-term settlement monitoring programs.

Lessons Learned

• Thin soft soil layers can be easily overlooked in initial borings.
• Multiple in-situ tests increase reliability of subsurface profiles.
• Proactive ground improvement avoids costly repairs later.

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

• Are multiple soil testing methods used to confirm subsurface conditions?
• Has ground improvement been considered for soft soils?
• Is settlement monitoring planned for critical foundation elements?