What is Geotextile?

Geotextiles are flexible, porous fabrics made from synthetic fibers like polypropylene or polyester, usually supplied in large rolls.

WHAT IT’S USED FOR

Separation

• Stops different types of soil or materials from mixing, helping each layer stay in place.
• Example: Keeping gravel from sinking into soft clay.

Stabilisation

• They help reduce movement between soil particles, making the ground firmer and more reliable.
• Example: Improving soft ground so it can support a building foundation.

Drainage

• They allow water to flow through or along them, helping to remove excess water efficiently.
• Example: Draining water along a road or behind a wall to prevent water buildup.

Filtration

• They allow water to pass through while holding back fine soil particles, keeping the soil stable.
• Example: Letting water drain from soil behind a retaining wall without losing soil.

Reinforcement

• They add strength to the soil, helping it support heavier loads and improving overall stability.
• Example: Strengthening soil under an embankment or road to carry traffic loads.

Protection

• They are used as a protective layer to prevent damage, erosion, and the movement of soil or fine materials.
• Example: Can be placed under gravel to protect the layer underneath from sharp stones.

Material Type

• Woven: stronger and more durable, but they drain poorly. They are used for reinforcement, road building and driveways.
• Non-woven: smoother, and allow better water flow. They are used for filtration, drainage, landscaping, and gardening.

HOW TO CALCULATE

• Geotextile should cover all areas in contact with soil, including the bottom of the gabions and the rear surfaces when used as a retaining wall.

• They are supplied in rolls, with each roll having a length and a height measured in meters.
• To find the total area (in square meters), multiply the length by the height.
• Example: A 10m × 4.5m geotextile roll covers an area of 45m².

HOW TO INSTALL

• Experience Required: Low
• Tools Required: Protection gloves, Spade, Spirit level, Utility knife
• Materials Required: Geotextile, Gravel

Step 1) Prepare the Area

• Prepare the subgrade properly. Remove sharp objects, roots, rocks, and other debris to prevent punctures.
• The surface should be clean and smooth, with all large stones, roots, and foreign materials removed.

Step 2) Dig & Level the Ground

• Dig a base.
• Level the ground to remove uneven areas that could cause the fabric to shift.
• For drainage, create a 1–2% slope to guide water flow, if needed.

Step 3) Position the Geotextile

• Start rolling out the fabric carefully.
• Lay it horizontally over the prepared surface, making sure it follows the terrain.
• Keep it taut, with no wrinkles or folds.

Step 4) Cut to Size

• Use a utility knife or sharp scissors to make small, precise cuts.

Step 5) Overlapping Fabric

• When joining geotextile, overlap by 30-60 cm, depending on soil conditions.
• For larger projects, use a greater overlap.

Step 6) Add Top Layer

• After placing the geofabric, add the upper layers such as gravel basecourse.
• Spread the material evenly to prevent the fabric from shifting.

Alternative: Vertical Application

• For vertical uses, like retaining walls, place the geotextile between the wall and the gabions.

FURTHER TIPS & READING

Further Tips

• For horizontal use, lay the geotextile flat on the soil with proper overlap to separate and stabilise the base layer.
• For vertical use, such as retaining walls, install it behind structures like gabions to allow drainage while preventing clogging.
• Dig and compact the base if the ground is soft or the structure will carry heavy loads.
• Geotextile is usually installed under gravel to stop it from sinking into the soil and to create a stable foundation. When placed above gravel, it mainly works as a separator, keeping layers clean rather than adding strength.
• Fix the fabric with pins or staples if necessary, as wind can shift it easily.
• Increase overlap on uneven ground for better performance.
• Avoid folds or gaps under the fabric, as they reduce its effectiveness.
• Correct installation can extend the lifespan of a structure by many years, while poor installation can make it ineffective. The material is only part of the system: correct installation is just as important.

FURTHER READING

• What is a Gabion? – Learn what a gabion is.
• How to Install Gabion Baskets – Step by step instructions for gabion basket installation.
• How to Fill Gabions – A simple guide to filling gabion baskets.

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