Case Study: Unanticipated Layer of Organic Soils Causes Embankment Failure in Florida (2019)

Project Overview
• Name: SR-528 Widening Project
• Location: Orlando, Florida
• Year: 2019
• Project Size: $350 million
• Scope: Highway widening with embankment construction over wetlands
• Lead Agencies/Contractors: Florida DOT /

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

Summary of the Issue, Problem, or Challenge
Organic-rich soil layers beneath embankment zone were not identified during initial investigations, leading to significant settlement and slope instability.

Root Cause Analysis

• Soil borings were sparse and missed localized organic soil pockets.
• Underestimation of compressibility and drainage characteristics of organic soils.
• Embankment design did not consider consolidation and creep of organic layers.

Impacts Due to the Issue, Problem, or Challenge

• Embankment slope failure during construction, halting work for 3 months.
• Increased costs for redesign, soil replacement, and drainage improvements.
• Long-term settlement monitoring required post-construction.

Corrective Actions Taken

1. Performed detailed soil sampling and lab testing for organic content and compressibility.
2. Removed organic soils and replaced with engineered fill in critical areas.
3. Installed wick drains and geosynthetics to accelerate consolidation.
4. Enhanced drainage systems and slope reinforcement measures.

Lessons Learned

• Organic soils require detailed investigation and specialized design considerations.
• Sparse soil borings risk missing localized weak layers.
• Ground improvement and drainage acceleration techniques critical in organic soils.

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

• Are soil borings dense enough to identify organic soil pockets?
• Has organic soil compressibility been tested and factored into design?
• Are ground improvement methods included for organic soil areas?