Reference date: May 2026 | Based on AASHTO M 288, ASTM D4595, and FHWA guidelines
Overview
Woven geotextiles are used in road construction to separate subgrade soil from aggregate base, distribute loads, and reinforce pavement sections. Selection depends on subgrade strength, traffic loading, and project specifications. This document summarizes technical specifications and selection criteria based on AASHTO M 288 and ASTM standards.
1. Geotextile Functions in Road Construction
Woven geotextiles installed between subgrade soil and aggregate base course perform three primary functions:
Separation
Prevents intermixing of subgrade soil and aggregate base, maintaining layer integrity and preventing contamination of the base course.
Stabilization
Provides lateral confinement to aggregate particles, increasing load-bearing capacity and reducing rutting.
Reinforcement
Distributes wheel loads over a wider subgrade area, reducing vertical stress and preventing deformation.
2. Technical Specifications
The following specifications are commonly referenced for road base geotextiles under AASHTO M 288:
| Property | Test Method | Class 1 (High Stress) | Class 2 (Moderate) | Class 3 (Separation) |
|---|---|---|---|---|
| Grab tensile strength (N) | ASTM D4632 | ≥ 1,350 N | ≥ 1,100 N | ≥ 900 N |
| Wide-width tensile (kN/m) | ASTM D4595 / ISO 10319 | ≥ 36 kN/m | ≥ 22 kN/m | ≥ 18 kN/m |
| CBR puncture (kN) | ASTM D6241 | ≥ 2.4 kN | ≥ 1.8 kN | ≥ 1.5 kN |
| Apparent opening size (mm) | ASTM D4751 | 0.15 – 0.43 mm | ||
| UV resistance (500 hr) | ASTM D4355 | ≥ 70% tensile retention | ||
3. Subgrade Classification and Geotextile Selection
Subgrade strength is typically measured by California Bearing Ratio (CBR). Selection guidelines per AASHTO M 288:
| Subgrade Condition | CBR Range | AASHTO Class | Min. Wide-Width Tensile |
|---|---|---|---|
| Strong | CBR ≥ 3 | Class 3 (Separation) | ≥ 18 kN/m |
| Moderate | CBR 1–3 | Class 2 (Stabilization) | ≥ 22 kN/m |
| Weak / Soft | CBR < 1 | Class 1 (Heavy Stabilization) | ≥ 36 kN/m |
4. Design Benefits
Field studies, including those summarized in FHWA Report FHWA-HRT-17-111, indicate that geotextile-stabilized base courses can deliver equivalent structural performance with 15–30% less aggregate thickness compared to unstabilized designs on subgrades with CBR below 3. Additional benefits include:
- Reduced maintenance frequency and life-cycle costs
- Extended pavement service life on weak subgrades
- Improved construction access over soft soils
- Consistent layer thickness and material separation
5. Installation Considerations
- Subgrade preparation: Clear vegetation, rocks, and debris. Fill soft spots and roughly grade the surface.
- Roll placement: Roll geotextile directly on prepared subgrade in the direction of construction.
- Overlaps: Minimum 0.3–0.5 m for separation applications; 0.5–1.0 m for stabilization on soft subgrades.
- Anchor edges: Use sandbags, soil, or stakes to prevent shifting during aggregate placement.
- Aggregate placement: Dump and spread aggregate from the sides, not directly onto the fabric from height. Minimum cover thickness: 150–200 mm.
6. Information to Prepare Before Ordering
To receive an accurate quotation, the following information is typically requested:
- Application: separation, stabilization, or reinforcement
- Subgrade CBR or soil classification (if known)
- Anticipated traffic loading (axle loads, passes per day)
- Required AASHTO M 288 class or tensile strength
- Roll width and roll length
- UV stabilization requirement (exposure duration)
- Estimated quantity (square meters, rolls, or containers)
- Destination port and preferred trade term
References
- AASHTO M 288-21. Geotextile Specification for Highway Applications. AASHTO, 2021.
- ASTM D4595. Standard Test Method for Tensile Properties of Geotextiles by the Wide-Width Strip Method. ASTM International.
- ASTM D4632. Standard Test Method for Grab Breaking Load and Elongation of Geotextiles. ASTM International.
- ASTM D6241. Standard Test Method for Static Puncture Strength of Geotextiles. ASTM International.
- FHWA-HRT-17-111. Geosynthetic Design and Construction Guidelines. Federal Highway Administration, 2017.
- Giroud, J.P. and Han, J. (2004). "Design Method for Geogrid-Reinforced Unpaved Roads." Journal of Geotechnical and Geoenvironmental Engineering.
Article ID: ROAD-GEO-001 | Last updated: May 2026