Overview
ISO/TR 18228-2:2021 - Design using geosynthetics - Part 2: Separation provides practical, non‑mandatory guidance for using geotextiles where the primary function is separation of soils and below‑ground structures in contact with natural soils and fills. Intended for geotechnical and civil engineers, the report focuses on installed soils, the installation process, and the strength and deformation behaviour of geosynthetics to ensure long‑term separation performance.
Key topics
- Separation function and scope - Guidance on when and how a geotextile should prevent mixing of dissimilar materials (subgrade vs. aggregate cover).
- Design concepts worldwide - Summaries of regional approaches, notably the German GRK (Geotextilrobustheitsklasse) classification and the American AASHTO M288 survivability approach.
- GRK robustness classes - Selection based on two main parameters: mass per unit area (ISO 9864) and strength/puncture resistance (ISO 12236 for non‑wovens, ISO 10319 for wovens). Example thresholds:
- Non‑woven: GRK 3 ≥ 1.5 kN & ≥ 150 g/m²; GRK 4 ≥ 2.5 kN & ≥ 250 g/m²; GRK 5 ≥ 3.5 kN & ≥ 300 g/m².
- Woven (tape/yarn): GRK 3 ≥ 35 kN/m & ≥ 180 g/m²; GRK 4 ≥ 45 kN/m & ≥ 220 g/m²; GRK 5 ≥ 50 kN/m & ≥ 250 g/m².
- Multifilament (PET): higher tensile thresholds and mass requirements for GRK 3–5.
- Installation and construction stresses - Classification of site stresses (AB1–AB5) by compaction, equipment, and rut depth (e.g., AB2: rut < 5 cm; AB3: 5–15 cm; AB4: 15–30 cm; AB5: > 30 cm). GRK selection is driven by both fill material characteristics (AS levels) and installation stress (AB levels).
- AASHTO M288 summary - Material survivability/specification for separation-only geotextiles, typically applicable where subgrade CBR ≥ 3% (unsaturated soils) and where hydraulic transmissivity is not critical.
Applications
- Road and pavement base stabilization where a geotextile prevents contamination of aggregate by subgrade soils.
- Temporary construction access, borrow pits and embankment layers requiring separation under traffic and compaction.
- Utility trenches and drainage systems where soil separation protects structural layers.
- Specification and procurement of geotextiles by design engineers, contractors, and material suppliers seeking survivability and robustness guidance.
Who should use this
- Geotechnical and civil engineers developing pavement and earth‑structure designs
- Specifiers and procurement teams preparing material requirements
- Contractors and site supervisors planning installation and compaction procedures
- Manufacturers and testing laboratories aligning products to GRK or AASHTO M288 criteria
Related standards
This report helps match geotextile properties (mass, puncture/tensile resistance) and installation practices to site conditions to maintain the separation function and extend service life.
