Geotextiles for Separation Function
topic
Separation geotextiles prevent intermixing of dissimilar soil layers — typically aggregate sub-base and weak subgrade — maintaining the structural integrity and drainage capacity of road and railway construction over design service lives of 20–50 years. Woven PP slit-film geotextiles (80–200 g/m², tensile strength 10–40 kN/m per ISO 10319, CBR puncture resistance 1,500–4,000 N per ISO 12236) are most commonly specified for road sub-base separation where trafficking loads of 100–300 kPa are applied. Nonwoven needle-punched PP (150–400 g/m²) provides conformability to irregular subgrade surfaces reducing installation damage. Opening size (O₉₀, ISO 12956) of 0.06–0.25 mm is selected to retain subgrade soil particles (D₉₀ ratio criterion: O₉₀ < D₉₀ soil) while allowing drainage. Separation geotextile installation extends unpaved road service life by 2–5× versus unprotected aggregate at added cost of $0.50–2.00/m², saving $15,000–40,000/km in aggregate replacement over 10 years. FHWA (USA) and Highways England specifications mandate geotextile separation in roads over subgrades with CBR below 3%. Annual global separation geotextile consumption exceeds 2.5 billion m².
Role
Separation geotextiles are the highest-volume geotech product globally, delivering the critical civil engineering function of preventing subgrade soil contamination of aggregate layers that would otherwise cause progressive structural failure of roads, railways, and airfields over their operational lifespan.