Case Study: Hidden Abandoned Mine Voids Delay Highway Project in Pennsylvania (2015)

Project Overview
• Name: PA Route 61 Realignment
• Location: Schuylkill County, Pennsylvania
• Year: 2015
• Project Size: $220 million
• Scope: Highway realignment and embankment construction
• Lead Agencies/Contractors: Pennsylvania DOT /

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

Summary of the Issue, Problem, or Challenge
Construction uncovered undocumented abandoned mine voids beneath the embankment, leading to ground instability and work stoppage.

Root Cause Analysis

  • Historical mine maps were incomplete or inaccurate.
  • Geophysical surveys to detect voids were not performed prior to construction.
  • Contract lacked provisions for unexpected underground voids.

Impacts Due to the Issue, Problem, or Challenge

  • Major project delays of 8 months to perform remediation and stabilization.
  • High costs incurred for grouting and void filling.
  • Safety hazards for workers and future users.

Corrective Actions Taken

  1. Conducted comprehensive geophysical surveys (ground-penetrating radar, seismic).
  2. Performed pressure grouting to fill voids and stabilize ground.
  3. Updated project risk management to include subsurface void risks.
  4. Revised contracts to address unknown underground conditions.

Lessons Learned

  • Historical site usage must be thoroughly researched.
  • Geophysical surveys are essential in areas with potential underground voids.
  • Contracts must allocate risks for hidden subsurface hazards.

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

  • Has subsurface void detection been conducted with geophysical methods?
  • Are historical site uses and maps reviewed comprehensively?
  • Are contracts explicit about risk allocation for unknown voids?
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