Case Study: Cost Overrun from Inaccurate Quantity Estimations on Chicago Deep Tunnel Project (Chicago, IL, 2008)

Project Overview
• Name: Chicago Deep Tunnel System Expansion
• Location: Chicago, Illinois
• Year: 2008
• Project Size: $1.4 billion
• Scope: Construction of underground stormwater tunnels to reduce flooding
• Lead Agencies/Contractors: Metropolitan Water Reclamation District of Greater Chicago /

Category of the Issue, Problem, or Challenge
• Quantity Estimation
• Cost Management

Summary of the Issue, Problem, or Challenge
Underestimation of excavation and concrete quantities led to significant cost overruns as actual volumes exceeded initial projections.

Root Cause Analysis

  • Inadequate Survey Data: Initial site surveys lacked detail leading to optimistic quantity assumptions.
  • Geological Variability: Unexpected soil and rock conditions increased excavation volumes.
  • Estimation Methodology: Use of outdated unit rates and insufficient cross-checks.
  • Contractor Input: Limited involvement of contractors during estimation phase reduced accuracy.

Impacts Due to the Issue, Problem, or Challenge

  • Cost overruns of about 16%.
  • Project schedule extended by five months.
  • Increased disputes and claims over quantities and payments.

Corrective Actions Taken

  1. Implemented detailed geotechnical and topographical surveys pre-bid.
  2. Adopted collaborative estimating involving contractors and engineers.
  3. Used updated unit cost databases reflecting current market conditions.
  4. Instituted periodic quantity re-measurements and adjustments during construction.

Lessons Learned

  • Accurate and detailed surveys are essential for reliable quantity estimates.
  • Collaboration during estimation improves accuracy and reduces disputes.
  • Ongoing measurement and adjustment controls cost impacts.

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

  • Are site surveys detailed and recent?
  • Is contractor input integrated into estimation?
  • Are quantity measurements updated during construction?
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