Case Study: Unforeseen Expansive Clay Delays Dam Embankment Construction in Texas (2019)
Project Overview
• Name: Lake Conroe Dam Rehabilitation
• Location: Montgomery County, Texas
• Year: 2019
• Project Size: $95 million
• Scope: Rehabilitation of earthen dam including embankment repairs
• Lead Agencies/Contractors: Texas Water Development Board /
Category of the Issue, Problem, or Challenge
• Geotechnical
• Differing Site Conditions
Summary of the Issue, Problem, or Challenge
Construction encountered expansive clay soils causing unexpected heaving and cracking in the embankment, leading to remediation efforts and delays.
Root Cause Analysis
- Incomplete identification of soil mineralogy and plasticity in site investigation.
- Lack of expansive soil testing during preliminary geotechnical work.
- Insufficient design for soil swelling pressures and moisture variations.
Impacts Due to the Issue, Problem, or Challenge
- Embankment construction halted for 4 months to address soil stability.
- Additional costs incurred for soil treatment and reinforcement measures.
- Risk of future embankment distress if not properly mitigated.
Corrective Actions Taken
- Conducted detailed expansive soil characterization including swell potential tests.
- Applied soil stabilization techniques such as lime treatment.
- Redesigned embankment layers to accommodate soil expansion.
- Established moisture control and monitoring programs.
Lessons Learned
- Expansive soils require early identification through specific testing.
- Design must account for volume changes due to moisture fluctuations.
- Monitoring during and after construction is essential for long-term stability.
Audit & Prevention: Project Control Questions to Ask on Future Projects to Help Control the Situation
- Have swell potential and plasticity index tests been conducted?
- Does design incorporate mitigation for soil expansion?
- Are moisture control and monitoring systems in place during construction?