Case Study: Cost Overrun Due to Unforeseen Soil Conditions at Central Artery Tunnel (Boston, MA, 2003)

Project Overview
• Name: Big Dig – Central Artery/Tunnel Project
• Location: Boston, Massachusetts
• Year: 2003 (construction phase)
• Project Size: Initially $14.6 billion; final costs exceeded $24 billion
• Scope: Urban highway tunnel and interchange construction beneath Boston
• Lead Agencies/Contractors: Massachusetts Turnpike Authority /

Category of the Issue, Problem, or Challenge
• Geotechnical
• Cost Management

Summary of the Issue, Problem, or Challenge
Unforeseen poor soil and groundwater conditions were encountered, requiring extensive redesign and additional foundation work. These issues led to major cost overruns during the tunnel excavation and support phases.

Root Cause Analysis

• Inadequate Site Investigation: Initial soil studies underestimated variability and extent of soft soils.
• Groundwater Management Challenges: High water inflows required expensive dewatering and waterproofing.
• Design Changes: Redesign of tunnel supports and foundations to accommodate poor soil increased costs.
• Contractual & Scope Management: Change orders and dispute resolution prolonged schedule and inflated costs.

Impacts Due to the Issue, Problem, or Challenge

• Overall project cost increased by more than 65%.
• Delayed completion, increased public scrutiny, and loss of trust.
• Substantial additional funding required from state and federal sources.

Corrective Actions Taken

1. Enhanced geotechnical investigations for remaining phases.
2. Implementation of risk-sharing contracts to better manage unforeseen conditions.
3. Improved project cost controls and scope verification processes.
4. Increased stakeholder communication and transparent reporting.

Lessons Learned

• Comprehensive soil and groundwater investigations are critical for accurate cost estimates.
• Early risk identification and contract strategies can mitigate cost exposure.
• Clear scope definition reduces costly change orders.

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

• Were site conditions fully investigated and verified before bidding?
• Is there a contingency budget for geotechnical uncertainties?
• Are contract provisions in place to manage scope changes effectively?