Coir is best known for erosion control, but some of its most valuable work happens out of sight, inside the road itself. Indian road and research agencies have tested coir in subgrades, drains and embankments for years.
Strengthening weak subgrades
Where a road is built on soft soil, woven coir laid over the subgrade separates it from the base layer and adds strength while the ground consolidates. Published Indian practice uses woven mats of 700 to 1,000 GSM to improve subgrade strength, especially on weak soils with a California Bearing Ratio of 4 or less. Buried under fill, coir has been found to stay intact for five to ten years.
A Tamil Nadu Agricultural University handbook records coir matting grades used on rural roads built under India’s national rural roads programme (PMGSY), in weights from about 400 to 900 grams per square metre.
Drains and capillary breaks
In pavement edge drains, coir acts as a filter, letting water through while holding soil back. Over about two to three rainy seasons, a natural soil filter forms behind it and the coir is no longer needed, which is exactly when it breaks down. Coir layers are also used as capillary breaks, stopping groundwater rising into the road structure.
Embankments and cuttings
Bare embankments and cut slopes are among the most common uses. India has a dedicated standard, IS 15872, for coir geotextiles used to control rainwater erosion on roads, railway embankments and hill slopes, and the Ministry of Railways has issued guidelines on erosion control and drainage of railway formations.
Field trials
Applications have been trialled with the Coir Board and engineering institutions including the College of Engineering Trivandrum, NIT Calicut and NIT Trichy, and in projects with Kerala’s Public Works Department.
Road applications are engineered. Grade, placement and overlaps should follow the project design and the relevant road agency guidance.
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