Case Study: Unexpected Fill Material Found Beneath Highway Embankment in Iowa (2019)

Project Overview
• Name: Iowa Highway 30 Reconstruction
• Location: Central Iowa
• Year: 2019
• Project Size: $180 million
• Scope: Highway reconstruction including embankment widening and bridge abutments
• Lead Agencies/Contractors: Iowa DOT /

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

Summary of the Issue, Problem, or Challenge
During embankment construction, previously undocumented fill material of poor quality was encountered, leading to redesign and removal of unsuitable soils.

Root Cause Analysis

• Historical site data failed to identify presence of undocumented fill.
• Initial soil investigations were limited and did not include detailed mapping of fill zones.
• Lack of thorough review of available historical records and aerial imagery.
• Contract did not fully address unknown fill conditions.

Impacts Due to the Issue, Problem, or Challenge

• Delay of 4 months due to excavation and replacement of unsuitable fill.
• Cost overruns from additional earthwork and disposal fees.
• Increased risk of future embankment settlement if poor fill was not removed.

Corrective Actions Taken

1. Expanded soil investigations including trenching and test pits for fill identification.
2. Developed removal and replacement specifications for unsuitable fill.
3. Updated project risk management and contract terms to address undocumented fill.
4. Implemented GIS-based mapping of subsurface conditions for future planning.

Lessons Learned

• Undocumented fill poses significant geotechnical risks if unidentified.
• Comprehensive investigations and historical research reduce surprises.
• Risk allocation in contracts should include unknown fill scenarios.

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

• Are undocumented fill areas identified prior to construction?
• Is removal and replacement procedure clearly specified?
• Are contracts structured to manage fill-related risks?