Reinforced Earth Retaining Walls: Causes of Failures, Design Guidelines & Construction Best Practices

Why Are Reinforced Earth Walls Failing Despite Good Infrastructure?

Reinforced earth retaining walls (REWs) are widely used in highway embankments, flyovers, and bridge approaches due to their space efficiency and cost-effectiveness. However, across various infrastructure projects in India, there has been a noticeable rise in structural failures of these retaining walls, even in well-managed highway construction projects.

These failures, though not always catastrophic, have damaged public trust, raised engineering concerns, and impacted the credibility of executing agencies. The issue is not about cost-cutting—it’s about poor adherence to engineering design principles, improper construction sequence, and lack of skilled supervision.

This Article covers:

• Why reinforced soil retaining walls fail
• Common construction mistakes
• Material specifications and testing
• Best practices for installation
• Engineering checks to ensure long-term performance

Why Do Reinforced Earth Walls Fail?

It’s Not Because of Contractor Negligence

Most failures are not due to contractors trying to save costs. In reality, low-quality work leads to recurring repairs, time delays, and reputational damage—which no serious contractor wants. So what’s going wrong?

Actual Reasons Behind Failures

The most common causes include:

• Lack of understanding of soil-reinforcement interaction
• Poor workmanship at site
• Ignoring correct construction sequencing
• Inadequate site-specific testing
• Improper or substandard materials

How Do Reinforced Earth Walls Work? The Design Philosophy

Reinforced earth walls rely on the interaction between compacted backfill soil and synthetic reinforcements (such as geogrids or geostrips) to create a stable, composite structure that resists lateral earth pressure.

Core Components of a Reinforced Earth Wall

1. Backfill Material – Must be well-graded, high-friction soil
2. Reinforcement Elements – Geogrids, geosynthetics, or metallic strips
3. Facing Panels – Precast concrete elements for aesthetics and erosion control

Working Principle

The system works on the principle of friction and interlocking:

• Soil has very good compressive strength but doesn’t have tensile strength capacity
• Through friction and interlocking, tensile strength is transferred to the geogrid element
• This increases the soil’s capacity to resist lateral earth pressure
• In some cases, earth pressure theoretically becomes zero at the end of the wall
• The facing panel works as a cosmetic element preventing soil erosion and providing aesthetic look

Design and Construction Best Practices for RE Walls

1. Design Validation and Standards Compliance

• Refer to MoRTH clauses 3102 to 3106 for specifications
• Clearly define soil type and backfill material properties
• Geogrid specifications should include tensile strength and durability
• Use third-party testing to confirm performance reduction factors

2. Mandatory Manufacturer Certifications

Before using geogrids or reinforcement materials, verify that the manufacturer provides:

• ISO certification
• Independent lab test reports
• Verified data for:
  • Creep reduction
  • Installation damage
  • Weathering resistance
  • Chemical compatibility

3. On-Site Testing: Don’t Skip It

Pull-Out Testing Requirements

• Use ASTM D6706 or equivalent
• Verify pull-out resistance
• Ensure proper soil-to-geogrid interaction
• Conduct tests randomly on-site using actual fill materials

4. Correct Construction Sequence

Improper sequencing is a key reason for structural failure.

Correct Steps:

1. Excavation
2. Ground improvement (if needed)
   • Check for black cotton soil or marine clay
   • Conduct SPT and plate load tests
   • Use methods like PVDs, stone columns, or sand drains
3. Filter media installation
   • Use 600 mm thick coarse aggregates or gravel
   • Avoid inappropriate substitutes like non-woven fabrics
4. Lay reinforcement properly
   • At right angles to the wall face
   • Aligned and spaced as per design
5. Backfilling and compaction
   • Compact in 200 mm layers
   • Use compaction equipment at least 2 meters from wall face
   • Achieve 97% MDD (Modified Proctor Density)

5. Facing Panels: Specifications and Supervision

• Minimum thickness: 180 mm (including branding/logo)
• Use inward batter of 1–2 degrees to prevent forward displacement
• Provide horizontal and vertical joint gaps
• Use EPDM pads between joints
• Inside joint areas should be covered with geotextile

6. Backfill Material Guidelines

• Minimum friction angle (φ) of 30 degrees
• Less than 15% passing 75-micron sieve
• Plasticity Index (PI) not more than 6
• Use of fly ash is acceptable only if tested and confirmed to meet specs

Site Supervision and Quality Control

Importance of Skilled Supervision

• Ensure trained supervisors are available on-site
• Follow layer-by-layer approval
• Conduct proper alignment and interlocking checks
• Monitor every layer before proceeding

Capping Beam and Crash Barrier Guidelines

• Use precast elements only
• Ensure crash barriers do not load the facing panels
• Prevent vertical pressure on the facade to avoid bulging or collapse

Performance Case Study: What Worked in the Past

From 2000 to 2005, projects like the Golden Quadrilateral and East-West Corridor under NHAI successfully implemented thousands of RE walls. These walls continue to perform well due to:

• Strict design discipline
• Certified and tested materials
• Ground improvement where necessary
• Professional site supervision

Recommendations for Engineers and Site Teams

• Focus on engineering first, not shortcuts
• Never compromise on approved materials or specifications
• Ensure everyone on-site is trained in the process
• Perform consistent testing and monitoring
• Collaborate with suppliers for supervision and technical support

Conclusion: Reinforced Earth Retaining Walls Work When Executed Properly

Reinforced earth walls are a reliable, proven, and cost-efficient solution for highway embankments and elevated infrastructure. The recent issues we see are not due to technology failures—they are execution errors.

To ensure long-lasting performance:

• Validate designs with certified inputs
• Use standard-compliant materials
• Stick to proper construction sequences
• Assign trained supervisors on-site
• Conduct all testing and inspections as specified

Remember: one missed step in construction can lead to long-term structural problems. But with proper training, design validation, and strict supervision, reinforced earth retaining walls can last for 30+ years without issues.