Case Study: Unexpected Rock Depth Variation Delays Highway Overpass in Colorado (2018)

Project Overview
• Name: I-70 Eagle County Bridge Reconstruction
• Location: Eagle County, Colorado
• Year: 2018
• Project Size: $120 million
• Scope: Bridge replacement with deep foundation piling
• Lead Agencies/Contractors: Colorado DOT /

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

Summary of the Issue, Problem, or Challenge
The depth to competent bedrock varied dramatically across the site, requiring redesign of pile lengths and causing significant schedule delays.

Root Cause Analysis

• Initial borings failed to capture lateral variability of bedrock depth.
• Insufficient density of geotechnical borings.
• Lack of adaptive foundation design flexibility.

Impacts Due to the Issue, Problem, or Challenge

• Delay of 6 months for redesign and extended piling work.
• Increased material and labor costs due to longer piles and equipment use.
• Potential safety issues with pile driving in unexpected soil conditions.

Corrective Actions Taken

1. Performed additional borings with denser spacing.
2. Redesigned foundation to allow variable pile lengths and embedment depths.
3. Introduced phased piling approach to adapt to subsurface conditions in real time.
4. Updated contract to share risks related to subsurface variability.

Lessons Learned

• Borings must be dense enough to detect lateral soil/rock variability.
• Foundation designs should incorporate flexibility for site variability.
• Contracts should address unexpected subsurface condition risks clearly.

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

• Is the geotechnical investigation dense and comprehensive enough?
• Does the foundation design allow for variability in soil/rock depths?
• Are contracts explicit on risk-sharing for differing subsurface conditions?