Geotextile - Types, Advantages and Functions in Civil Enginnering

Geotextiles are permeable or porous fabrics, made from synthetic materials that are used in association with soil, have the ability to separate, filter, reinforced, and drain.

 As per ASTM, geotextiles are permeable sheets of synthetic fiber like polyester, polypropylene, nylon, viscose, etc. Geotextile fabrics come in three basic forms: woven (resembling mail bag sacking), needle punched(resembling felt), or heat bonded(resembling ironed felt). Geotextiles are available in thickness varying from 10 to 300 miles(1 mil=1/100 inch=0.254mm)and in widths up to 10 m and in rolls length up to 600 m. The permeabilities  of geotextiles sheets are comparable in the range from coarse gravel to fine sand.

Geotextile can be made of a wide variety of natural shavings etc. and synthetic materials and can be woven, made up to monofilament, multifilament on tapes, or non woven i.e., mechanically bonded (needle punched), heat bonded or resin bonded. They may also be knitted sometimes.

What is geotextile in civil engineering?

Geotextiles are very useful material in civil engineering works. Geotextiles are used in the construction of roads, highways, railways, airports, bridges, and tunnels.

Types of Geo Textile

Geotextiles are used in both large scale civil engineering projects and small. The geotextile is further prepared in three different categories –

1. 1)  Woven Fabrics

2. 2)  Non-woven Fabrics

3. 3)  Knitted Fabrics

Woven Fabrics – 

The most commonly found geotextiles are the woven which are similar to weaving usual clothing textiles. They are high tensile strength and load capacity hence used when you need something very sturdy & durable. Woven fabrics are often created on a loom, and made of many threads woven on a warp and weft.

 

WOVEN FABRICS

Non-woven Fabrics –

Non-woven geotextiles are made of 100% staple polyester and polypropylene needle punched filter fabric. The bonding of fibers is done using thermal, chemical, or mechanical techniques or a combination of techniques. They have excellent water flow rates and drainage for the filtration of soil fines but they have a shorter life than woven geotextiles.

NON-WOVEN FABRICS

Knitted fabrics – 

The knitting process consists of interconnecting loops of yarn on powered automated machines. Knitted geotextiles are a subset of woven geotextiles and are mostly as filters on pipes as in two-stage filter applications.

Apart from these three geotextiles, other geosynthetics used are geonets, geogrids, geocells, geomembranes, geocomposites, etc.

 

KNITTED FABRIC

Advantages of geotextiles:-

The biodegradable nature of natural fibers have restricted their use to some specific applications whereas synthetic materials have made their way for wide applications. Another advantage of using these fibers for geotextiles are related to their ability to be engineered chemically, physically and mechanically to suit particular geotechnical engineering applications.

Functions of Geotextiles:-

The functions of geotextiles can be broadly divided into two heads – 

                         1) Hydraulic functions

•       Fluid transmission or drainage

•       Filtration

                        2) Mechanic functions

•      Separation

•       Protection

•       Reinforcement.

USE OF GEOTEXTILES IN EARTHEN DAM CONSTRUCTION

In earthen dams, the upstream and downstream slopes are prone to erosion. Hence geotextiles can be effectively and conveniently used as filter media in erosion control of earthen dam slopes.

In earthen dams, geotextiles can be used in many important positions for filtration, drainage and erosion control functions such as the follows:

• Erosion control or slope protection function.

• Filtration and drainage material for seepage control system

• Filtration and separation function.

• Filter wraps around PVC, perforated rigid pipes.

USE OF GEOTEXTILES IN ROAD WORKS

In many places in India, the high water table of the subgrade is a constant concern to read engineers. Geotextiles in the subgrade-subbase interface of a road can effectively deal with this problem.

Provision of geotextiles in road works may serve three functions:

Separator function

Drainage function

Reinforcement function

The function of geotextile as a separator in road work

Geotextile materials provide separation, which preserves the integrity and extends the life of the road surface layer. Roadway pavements are basically structures for taking high contact pressures from the vehicle tries and reducing these pressures through the depth of the pavement to a level that can be supported by the underlying soil/sub-grade.

If geotextile is not provided at the interface between sub-grade and the aggregate base, the vehicle pressure, over time, causes sub-grade soils to migrate into the aggregate base of the pavement section.

Geotextiles also function as filters and separators which –

1) Prevent the interpenetration of the natural soil and aggregates.

2) Fully preserves the properties of road-making materials,

3) Allows vehicles to circulate on the foundation course while working is in progress and protects the foundation course from contamination.

Drainage function of geotextile in road work

Also, using geotextiles to its drainages function, geotextile road edge drains can be laid to provide drainage of roads and hence improving them.

Lastly, when a road embankment is to be constructed on compressible soil, the consolidation of the sub-grade soil, over a period of time will cause cracks and pot in the road surface. To avoid this, usually the procedure is to provide sand drains that accelerate the consolidation process prior to road surfacing. The action can be more effectively achieved by the provision of geotextiles to provide vertical and horizontal drainage systems.

Reinforcement function of geotextile in road embankments

The geotextile layers are placed across the potential rotational failure plane to carry the tensile forces that cannot be carried by an unreinforced soil mass of the embankment.

 

USE OF GEOTEXTILES IN RAILWAYS WORKS

Geotextiles can be used in railways works to provide the following:

•  Separation function

• Reinforcement function

• Water drainage function                            

Separation Function –

In track foundation, geotextiles separate ballast and subgrade at the interface and prevents intermixing of the two materials under dynamic loads.

Geotextile also checks mud pumping and prevents ballast fouling and thus extends deep screening cycle by several years.

Reinforcement Function –

Geotextile provides reinforcement, through both tensioned membrane and ‘tensile member’ functions.

Drainage Function –

Geotextiles provide surface and subsurface drainage by wicking action under train loads, whereby water is squeezed and conveyed laterally out of track foundation. This action dries the subgrade, which in turn enhancing the soil supporting strength.

USE OF GEOTEXTILES IN EROSION CONTROL

Geotextiles can be used in erosion control to provide the following:

Soil slope retention – Geotextile on a bare slope decreases water runoff velocity until seed germination can occur. Acting in place of much and tack coat, the geotextile has far better uniformly and tensile strength.

Slope protection under liner – Stone rip rap, a common method of slope protection, should never be laid on a base slope. Geotextile laid on the soil under the rip rap can successfully substitute for expensive soil filters for illustration.

Grout filled mattresses – A mattress of controlled thickness results from two geotextiles separated by a drop stitch and pumped full of cement grout. The shape follows the ground surface contours and when properly toed in the bottom and anchored at the top, provide excellently erosion protection.

 

USE OF GEOTEXTILES IN BEARING CAPACITY IMPROVEMENT

Model studies by several investigations have clearly indicated the advantages and possibilities for improvement in bearing capacity and stiffness of the load settlement behavior by reinforcing the foundation soil. The reinforced soil technique concept is essentially based on the mobilization of the interfacial shearing resistance between the soil and reinforcement which in turn restrains the lateral deformation of the soil. Thus the effect of the reinforcement is to check the lateral flow of soil beneath the footing by introducing lateral confinement.

 

How to place of Geotextiles?

The following points are important:-

1) The ground surface that receives the geotextiles should be prepared for a relatively smooth condition, free of obstruction, depression, and debris.

2) Geotextiles used along channels should be with the machine direction of the material parallel to the channel.

3) If additional sheets are required to reach the top of the channel, the upslope sheet should overlap the downslope sheet.

4) Geotextiles used for 2 to 1 slope or greater should be placed with the machine direction of the geotextile sheets perpendicular to the top of the slope.

5) If successive sheets are required, they should be overlapped so that the upstream sheet is placed over the downstream sheet.

 

Some other information:-

1) Adjacent pieces of geotextiles may be joined by sewing or overlapping, though in most cases overlapping is preferred. When geotextile sheets are overlapped, they must be pinned.

2) The minimum overlap should be 450 mm. When the geotextiles are placed underwater, the minimum overlap should be 900 mm.

3) Geotextiles should be protected from direct sunlight, ultraviolet rays, water, debris. Any of these affect the strength, toughness, and permeability of geotextiles.