Road Embankment Design: AASHTO & FHWA Guide
The Road Embankment Calculator quantifies fill volume, topsoil, compaction, settlement, and reinforcement for stable road construction per AASHTO and FHWA standards. This guide covers side slopes, subgrade improvement, geogrid spacing, and cost estimation.
What is a Road Embankment?
Raised earth structure supporting pavement. Components:
- Subgrade: Prepared native soil
- Select Fill: Compacted granular
- Side Slopes: 2:1 to 4:1
- Topsoil: Stripped and stockpiled
Why Accurate Calculation Matters?
Prevents:
- Settlement: > 6 in post-construction
- Slope Failure: Shear instability
- Cost Overrun: 15–25% fill waste
- Pavement Distress: Cracking
Use with our Aggregate Calculator for subbase.
Standard Side Slopes
| Soil Type | Slope (H:V) | Max Height |
|---|---|---|
| Granular | 1.5:1 | 20 ft |
| Silty | 2:1 | 15 ft |
| Clay | 3:1 | 10 ft |
How to Build Embankment
Step-by-step:
- Strip Topsoil: 6–12 in
- Proof Roll: Subgrade CBR ≥ 3%
- Place Fill: 8–12 in lifts, 95% Proctor
- Compact: Vibratory roller
- Bench Slopes: For H > 10 ft
Our calculator automates volume and settlement.
Practical Applications
Used for:
- Highways: Interchange ramps
- Local Roads: Grade separation
- Airports: Runway fill
- Railways: Track bed
Pair with our Concrete Calculator for curbs.
Tips for Stability
Best practices:
- Geogrid: Every 2 ft for CBR < 3%
- Drainage: 4% cross-slope
- Erosion Control: Seed + mulch
- Settlement Plate: Monitor consolidation
Common Mistakes to Avoid
Avoid:
- Steep Slopes: Without reinforcement
- Poor Compaction: < 95%
- No Topsoil Strip: Organic settlement
- Ignoring CBR: Base failure
Advanced Considerations
For complex cases:
- Wick drains for clay
- Lightweight fill (EPS)
- Global stability analysis
- Seismic design
Conclusion
Road embankments are the foundation of durable pavements. Our Road Embankment Calculator delivers code-compliant quantities and stability checks instantly. Combine with our Steel Weight Calculator for guardrails. Explore our full suite of Construction Calculators for complete roadway design.