Geotextile is a synthetic permeable textile material used to improve the soil characteristics. It has the ability to separate, filter, reinforce, protect and drain when used in association with soils. Geotextiles are ideal materials for many infrastructure works such as roads, , landfills, drainage structures, and other civil projects.
Types of Geotextile
Geotextiles are made up of polymers such as polyester or polypropylene. They are divided into 3 categories on the basis of the way they are prepared :
1) Woven Fabric Geotextiles
2) Non-Woven Geotextiles
3) Knitted Geotextiles
1. Woven Fabric Geotextile
Commonly found geotextiles are of the woven type and are manufactured by adopting the techniques which are similar to weaving usual clothing textiles. This type has the characteristic appearance of two sets of parallel threads or yarns. The yarn running along the length is called warp and the one perpendicular is called weft. (As shown in the figure below)
2. Non-Woven Geotextile
Non-woven geotextiles manufactured from either continuous filament yarn or short staple . The bonding of fibers is done using thermal, chemical or mechanical techniques or a combination of techniques.
Geo-fibers obtained from mechanical interlocking or chemical or thermal bonding have a thickness of 0.5-1 mm while chemically bonded non-wovens are comparatively thick usually in the order of 3 mm.
3. Knitted Geotextile
Knitted geotextiles are manufactured by the process of interlocking a series of loops of yarn together. All of the knitted geosynthetics are formed by using the knitting technique in conjunction with some other method of geosynthetics manufacture, such as weaving.
Apart from these three geotextiles, other geosynthetics used are geonets, geogrids, geo-cells, geomembranes, geocomposites, etc. each having their own distinct features and uses for special applications.
Recommended Read:Geosynthetics in Civil Engineering and Construction Works
Functions of Geotextiles
The mode of operation of a geotextile in any application is defined by six discrete functions :
The separation function of geotextile is majorly used in the construction of roads. Geotextile prevents the intermixing of two adjacent soils. For example, by separating fine subgrade soil from the aggregates of the base course, the geotextile preserves the drainage and the strength characteristics of the aggregate material.
Some of the applicable areas are:
- Between subgrade and stone base in unpaved and paved roads and airfields.
- Between subgrade in railroads.
- Between landfills and stone base courses.
- Between geomembranes and sand drainage layers.
The equilibrium of geotextile-to-soil system that allows for adequate liquid flow with limited soil loss across the plane of the geotextile. Porosity and permeability are the major properties of geotextiles which involve infiltration action.
A common application illustrating the filtration function is the use of a geotextile in a pavement edge drain, as shown in the figure above.
Introduction of geotextile in the soil increases the tensile strength of the soil the same amount steel does in concrete. The strength gain in soil due to the introduction of geotextile is by the following 3 mechanisms :
- Lateral restraint through interfacial friction between geotextile and soil/aggregate.
- Forcing the potential bearing surface failure plane to develop an alternate higher shear strength surface.
- Membrane type of support of the wheel loads.
A layer of non-woven geotextile is impregnated in between existing and new asphalt layers. The geotextile absorbs asphalt to become a waterproofing membrane minimising flow of water into the pavement structure.
Uses of Geotextile in Construction
The scope of geotextile in the engineering field is very vast. The application of geotextile is given under the heading of the nature of work.
1. Road Work
Geotextiles are widely used in the construction of the road. It reinforces the soil by adding tensile strength to it. It is used as a rapid de-watering layer in the roadbed, the geotextiles need to preserve its permeability without losing its separating functions.
2. Railway Works
The woven fabrics or the non-woven ones are used to separate the soil from the sub-soil without impeding the groundwater circulation where the ground is unstable. Enveloping individual layers with fabric prevents the material from wandering off sideways due to shocks and vibrations from running trains.
It is used for mud control. For the improvement of muddy paths and trails those used by cattle or light traffic, nonwoven fabrics are used and are folded by overlapping to include the pipe or a mass of grit.
The use of geotextiles to filter the soil and a more or less single size granular material to transport water is increasingly seen as a technically and commercially viable alternative to the conventional systems. Geotextiles perform the filtering mechanism for drainages in earth dams, in roads and highways, in reservoirs, behind retaining walls, deep drainage trenches, and agriculture.
5. River, Canals and Coastal Works
Geotextiles protect river banks from erosion due to currents or lapping. When used in conjunction with natural or artificial enrockments, they act as a filter.