Interesting Facts to Learn About Geotextile

A geotextile is a permeable fabric, usually made from synthetic fibres, that is placed in or on soil. Water passes through it while soil particles are held back, and the synthetic polymers it is made from do not rot in the ground.

Geotextiles were first used as a replacement for graded soil filters. Depending on how a fabric is made, it can separate, reinforce, filter, protect or drain. Geotextiles are one family within the wider group of geosynthetics, and they are used mainly in civil and environmental engineering projects.

1. History of Geotextile

Geotextiles were originally called filter fabrics. In the late 1950s, R.J. Barrett in the United States began using them in erosion control work: behind precast concrete sea walls, under large stone riprap and beneath precast concrete erosion control blocks. He used woven monofilament fabrics with 6 to 30% open area. These fabrics let water through while retaining soil, and they were durable and stretched enough to stay in contact with the soil, which made them suitable as filters.

The idea is much older than synthetic fabrics. Builders in the ancient world, including in Egypt, laid mats of reed, grass or linen in soil, and natural fibres or vegetation were mixed with soil to make roads more stable.

2. Features of Geotextile

A geotextile has to let water and air move between soil layers: rainwater has to soak in, excess water has to drain out without carrying soil with it, and in some uses plant roots have to grow through. Its properties fall into four groups:

• Physical properties: specific gravity, mass per unit area (GSM), thickness and stiffness.
• Mechanical properties: tensile strength, elongation, tear strength, puncture and bursting strength, flexibility, drapeability and frictional resistance against soil.
• Hydraulic properties: permeability (permittivity), in-plane flow (transmissivity) and filtration (apparent opening size).
• Durability properties: resistance to abrasion, long-term clogging, UV light, chemicals, hydrolysis and biological attack.

3. Categories of Geotextile

Geotextiles come in many forms. The three main types are woven, non-woven and polyspun (spunbond).

Woven Geotextile

Woven geotextiles are used mainly for separation and reinforcement. They have high tensile strength and low elongation, so they carry load well under road bases and embankments. They are permeable, but less so than non-wovens, and they are not used as drainage layers.

Non-woven Geotextiles

Non-woven geotextiles are felt-like fabrics. They stretch more and have lower tensile strength than wovens of the same weight, but they are better at separation, drainage, filtration and cushioning. That makes them the usual choice for drains, hardscape sub-bases, erosion control and as a protection layer under geomembranes.

Polyspun Geotextiles

Polyspun geotextiles are also non-woven, and separation is their main function. They are permeable, so water drains through, but they add no reinforcement. They are typically used as weed barriers.

4. Fibers Used For Geotextiles

Geotextiles are made from both natural and synthetic fibres.

Natural geotextiles, mainly jute and coir, are chosen when the fabric should biodegrade after a few seasons, for example to hold soil on a slope until vegetation takes over.

Most geotextiles are synthetic. Four polymers account for nearly all of them: polyester, polyethylene, polyamide and polypropylene.

5. Applications of Geotextiles

Geotextiles are used in roads, ponds, pipelines, embankments, retaining walls and drains. In every case the fabric does one or more of six jobs: separation, filtration, reinforcement, drainage, protection and containment (as in geobags and geotubes).

Application in Dam Construction

Geotextiles are widely used in embankment dams. Their use in critical zones is limited because they can be damaged during installation and can clog over time, so a dam designer has to account for both before specifying one.

In dams, geotextiles do three things:

Filtration & Drainage

A geotextile filter controls seepage through and under an embankment dam: water passes, and the soil particles it would otherwise carry out of the embankment stay in place.

Protection and Separation

The most common use is as a separator between zones of different material, so fines from one zone do not migrate into and contaminate the next.

Surface Stabilization

Under riprap or concrete blocks, a geotextile forms part of the armour system that limits erosion of the dam faces, and during construction it can reduce sediment washing off exposed slopes.