Case Study: Owner-Imposed Material Substitution Causes Structural Failures in Retaining Walls (Nevada, 2018)
Project Overview
• Name: US-95 Corridor Safety Enhancements
• Location: Clark County, Nevada
• Year: 2018
• Project Size: $270 million
• Scope: Retaining walls, culverts, and safety barrier systems for highway widening
• Lead Agencies/Contractors: Nevada DOT (Owner) /
Category of the Issue, Problem, or Challenge
• Contract Owner
• Material Specification & Procurement
Summary of the Issue, Problem, or Challenge
Mid-project, the owner directed substitution of reinforced concrete block materials to reduce cost. Within weeks of installation, cracking and deformation were observed in completed retaining wall sections.
Root Cause Analysis
- Substituted blocks had lower compressive strength than originally specified.
- No re-analysis of wall design to accommodate change.
- Owner skipped independent material performance testing.
Impacts Due to the Issue, Problem, or Challenge
- Partial removal and rebuild of over 1,200 feet of retaining walls.
- Schedule setback of 4.5 months.
- $6.5 million cost increase, borne partially by the owner.
Corrective Actions Taken
- Reinstated performance-based specifications with third-party testing.
- Material substitutions now require contractor and engineering team concurrence.
- NDOT revised its internal approval workflows for design changes.
Lessons Learned
- Material substitutions must undergo technical evaluation and design verification.
- Cost savings should not compromise structural integrity.
- Owner-led changes must follow documented engineering sign-off protocols.
Audit & Prevention: Project Control Questions to Ask on Future Projects to Help Control the Situation
- Has the proposed material been tested and verified for performance equivalency?
- Was the structural design reviewed for compatibility with material changes?
- Are all change directives documented and traceable to engineering approvals?