Case Study: Unexpected Karst Void Found During Highway Embankment Construction in Kentucky (2017)

Project Overview
• Name: KY-90 Improvement Project
• Location: Pulaski County, Kentucky
• Year: 2017
• Project Size: $120 million
• Scope: Highway embankment and roadway widening
• Lead Agencies/Contractors: Kentucky Transportation Cabinet /

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

Summary of the Issue, Problem, or Challenge
Construction revealed previously unknown karst voids beneath embankment area, requiring extensive ground stabilization and redesign.

Root Cause Analysis

• Initial site investigations missed karst features due to limited geophysical survey.
• Lack of detailed sinkhole and subsurface cavity mapping in project area.
• Design did not anticipate high karst risk, leading to inadequate foundation preparation.

Impacts Due to the Issue, Problem, or Challenge

• Work stopped for 5 months to perform grouting and void filling.
• Project costs increased due to additional ground improvement measures.
• Safety concerns for workers and future roadway users.

Corrective Actions Taken

1. Conducted thorough geophysical surveys (electrical resistivity, ground-penetrating radar).
2. Applied pressure grouting and compaction grouting to fill voids.
3. Modified embankment design to include reinforced foundation layers.
4. Implemented karst risk assessment protocols for future projects.

Lessons Learned

• Karst terrains require specialized geophysical investigations pre-construction.
• Designs must include contingencies for subsurface voids in karst areas.
• Early detection prevents costly delays and safety risks.

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

• Are karst risk assessments performed early in project planning?
• Have appropriate geophysical surveys been completed?
• Are void mitigation and monitoring plans included?