Importance of Geotextile in Road Construction

A geotextile is a permeable synthetic fabric laid between soil layers. In road construction its main jobs are separation and filtration: it keeps the aggregate base from punching into a soft subgrade, and it keeps fine soil from migrating up into the aggregate while still letting water pass.

That matters because a road base fails when its stone gets contaminated with clay or silt, or when the stone is pushed down into wet subgrade. A geotextile at that interface keeps the base layer clean and at its design thickness, so weak or wet ground can carry a road without being dug out and replaced. Geotextiles are also used in buildings, dams, railways and embankments for the same reasons.

Geotextiles are made from synthetic fibres (polypropylene or polyester), or from natural fibres such as jute and coir for short-term erosion control. Placed in the soil, they add frictional resistance at the soil interface, spread loads and can shift the potential bearing-failure surface deeper, which raises the load the subgrade can carry.

Because they are permeable, geotextiles let water flow through them, so they can protect soil from wind and water erosion without trapping water behind them. In India, their use in pavements is covered by IRC:SP:59, the Indian Roads Congress guidelines for geosynthetics in road pavements, and by MoRTH specifications.

They are usually cheaper and faster than the alternatives for bad ground, which are replacing unsuitable soil or carrying the structure on deep foundations. Road building still depends on equipment such as motor graders, but a geotextile layer can reduce how much excavation and imported aggregate a job needs.

Geotextiles are a standard part of road construction, and the sections below cover the main types and functions.

Uses of Woven Geotextile

Woven geotextiles are made by interlacing strands at right angles, much like burlap. The weave pattern sets the fabric’s opening size and strength. Woven geotextiles generally let water through less freely than non-wovens, but they have high tensile strength and low elongation. On roads they are used as a separation and stabilisation layer over soft subgrade, where they hold the aggregate in place under traffic and reduce rutting.

Uses of Non-Woven Geotextile in Road Construction

Non-woven geotextiles are made by needle-punching or heat-bonding fibres into a felt-like sheet. They stretch more than woven fabrics before breaking, which lets them conform to uneven subgrade without tearing. Thicker needle-punched non-wovens also carry water along the plane of the fabric, which is useful when the geotextile has to drain water away from the soil or the road, for example as a filter wrap in edge drains.

Reinforcement Applications on Road Construction

A high-strength geotextile placed over weak subgrade, with a granular layer (sand or aggregate) compacted on top, spreads wheel loads over a wider area. This reduces rutting and stops sudden grooves forming in the road. For heavier reinforcement demands, designers often move to a geogrid, which interlocks with the aggregate.

Particle Separation

Separation is the most common reason to use a geotextile under a road. Without it, fines from a soft subgrade pump up into the aggregate base under repeated loading, and the stone is pushed down into the soil. Both reduce the effective thickness of the base. A geotextile between the two layers keeps them apart while letting water pass, so the base keeps its strength and drainage.

Types of Geotextile

Geotextiles are usually made from polypropylene or polyester. Polypropylene is light, strong and resistant to most chemicals in soil. Polyester is denser, has lower creep under sustained load, and suits most soil environments, though it is less resistant to highly alkaline conditions.

There are two main types: woven and non-woven. Non-woven geotextiles are three-dimensional structures of fibres laid in a random network.

They are used for subsurface drainage, erosion control, slopes and roads, and widely in landfills, road and railway construction, land reclamation and sea defence.

Woven geotextiles are made by interlacing tapes or yarns. In road construction they separate aggregate layers from the subgrade and support the ground under the road and pavement.

Purpose of Geotextile in road construction and maintenance

Geotextiles in road construction do mechanical and hydraulic work. Water passes through them while soil particles stay in place. They are used for filtration, for strengthening weak soils and improving bearing capacity, and for keeping fine and coarse particles apart.
Compared with traditional construction materials, geotextiles:

• Are uniform, factory-made materials, unlike natural soils that vary across a site
• Are usually cheaper to buy, transport and place than the equivalent thickness of soil or aggregate
• Are readily available and quick to install
• Reduce the quarrying and haulage of aggregate a road needs

Geotextile Testing

Testing confirms that a geotextile delivered to a road or highway job meets the specified properties. Common tests include direct shear (ASTM D5321), compressive creep, tensile creep and creep rupture (ASTM D5262), resistance to perforation by the cone drop test (ISO 13433), trapezoid tear strength (ASTM D4533) and grab tensile strength (ASTM D4632).

Testing should be done by an experienced lab using a tensile testing machine and friction (shear) apparatus, with the test set chosen for the application. The most common tests are puncture resistance and grab tensile strength.

Tests used to check geotextile strength include:

• Mass per unit area (ASTM D5261) and thickness (ASTM D5199), checked first to confirm the roll is the specified grade
• Grab tensile test (ASTM D4632)
• CBR puncture test (ASTM D6241)
• Trapezoid tear test (ASTM D4533)
• Wide width strip tensile test (ASTM D4595)
• Seam strength test for sewn seams (ASTM D4884)