Functions of Geotextiles in Civil Engineeing

Geotextiles, a newly emerging field in the civil engineering and other fields, offer great potential in varied areas of applications globally. Geotextiles play a significant part in modern pavement design and maintenance techniques. The growth in their use worldwide for transportation applications in particular, has been nothing short of phenomenal. Geotextiles are ideal materials for infrastructural works such as roads, harbors and many others. They have a bright future, thanks to their multifunctional characteristics. The paper provides an overview of various natural as well as synthetic textile fibres used for application as geotextiles

Functions of Geotextiles:
Every textile product applied under the soil is a geotextile. The products are used for reinforcement of streets, embankments, ponds, pipelines, and similar applications. Depending on the required function, they are used in open-mesh versions, such as a woven or, rarely, warp-knitted structure, or with a closed fabric surface, such as a non-woven. The mode of operation of a geotextile in any application is defined by six discrete functions: separation, filtration, drainage, reinforcement, sealing and protection. Depending on the application the geotextile performs one or more of these functions simultaneously.

Separation is defined as, “The introduction of a flexible porous textile placed between dissimilar materials so that the integrity and the functioning of both the materials can remain intact or be improved”. In transportation applications separation refers to the geotextile’s role in preventing 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. The effect of separation is illustrated in below.  
Geotextile in separation
 They are used in all classes of roads and similar civil foundation as the base of construction on contaminated layer is the single most cause of premature failure. The use of separator prevents pumping effect created by dynamic load and also helps the passage of water while retaining soil particles. In theses types of geotextiles, thickness and permeability are most important characteristic properties. 
Some of the applications areas are:
  1. Between subgrade and stone base in unpaved and paved roads and airfields
  2. Between subgrade in railroads
  3. Between land fills and stone base courses
  4. Between geomembranes and sand drainage layers
  5. Beneath sidewalks slabs
  6. Beneath curb areas
  7. Beneath parking lots
  8. Beneath sport and athletic fields
It is defined as “the equilibrium geotextile-to-soil system that allows for adequate liquid flow with limited soil loss across the plane of the geotextile over a service lifetime compatible with the application under consideration”. In filtration, fabrics can be either woven or non-woven, to permit the passage of water while retaining soil particles. Porosity and permeability are the major properties of geotextiles which involves in filtration action. Application helps the replacement of graded aggregate filters by a geotextiles warping. These applications are also suitable for both horizontal and vertical drains. A common application illustrating the filtration function is the use of a geotextile in a pavement edge drain, as shown in below.
Geotextile in filtration
Drainage (Transmissivity):
This refers to the ability of thick nonwoven geotextile whose three-dimensional structure provides an avenue for flow of water through the plane of the geotextile. Figure 6 also illustrates the transmissivity function of geotextile. Here the geotextile promotes a lateral flow thereby dissipating the kinetic energy of the capillary rise of ground water.

This is the synergistic improvement in the total system strength created by the introduction of a geotextile into a soil and developed primarily through the following three mechanisms:
  1. Lateral restraint through interfacial friction between geotextile and soil/aggregate
  2. Forcing the potential bearing surface failure plane to develop at alternate higher shear strength surface
  3. Membrane type of support of the wheel loads.
In this method, the structural stability of the soil is greatly improved by the tensile strength of the geosynthetic material. This concept is similar to that of reinforcing concrete with steel. Since concrete is weak in tension, reinforcing steel is used to strengthen it. Geosynthetic materials function in a similar manner as the reinforcing steel by providing strength that helps to hold the soil in place. Reinforcement provided by geotextiles or geogrids allow embankments and roads to be built over very weak soils and allows for steeper embankments to be built.

Sealing Function:
A non-woven geotextile performs this function when impregnated with asphalt or other polymeric mixes rendering it relatively impermeable to both cross-plane and in-plane flow. The classic application of a geotextile as a liquid barrier is paved road rehabilitation, as shown in below. Here the non-woven geotextile is placed on the existing pavement surface following the application of an asphalt tack coat. The geotextile absorbs asphalt to become a waterproofing membrane minimizing vertical flow of water into the pavement structure. 
Geotextile in sealing function

About the Editor-in-Chief:

Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.

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