About Geo Textiles

• Geotech segment comprises of technical textile products used in Geotechnical applications pertaining to soil, rock, earth etc.
• This class of product is loosely called Geotextiles.
• However Geotextiles particularly refers to permeable fabric or synthetic material, woven or non-woven, which can be used with geotechnical engineering material.
• The principal functions performed by Geotextiles are
  1. Confinement /separation,
  2. Reinforcement,
  3. Filtration and drainage, and
  4. Protection.
• Application areas include Civil Engineering
  1. Roads and pavements,
  2. Slope stabilization and embankment protection,
  3. Tunnels,
  4. Rail-track bed stabilization,
  5. Ground stabilization and drainage etc),
  6. Marine engineering (soil erosion control and embankment protection, breakwaters) and
  7. Environmental engineering (landfills and waste management).
• Other specialized Geotech products comprise
  1. Geogrids -- plastics filaments and tapes etc formed into a very open, grid like configuration having large apertures
  2. Geonets -- extruded polymer ribs set in net like fashion with small apertures),
  3. Geomembranes -- impermeable fabric as barrier and
  4. Geocomposites-- products using two or more Geotextiles e.g. Pre-fabricated Drains-PVD).

Product characteristics

• In general, the greater part of Geotextiles is manufactured from raw materials like polypropylene (PP), polyethylene or polyester which later formed into fabrics based on kind of practice.
• The mechanical and hydraulic properties vary widely depending on type of application designed for.
  1. Depending on type (woven/non-woven),
  2. Process (thermal bonded/resin bonded),
  3. Desired performance specifications (load bearing ability, tear resistance etc),
• Geotextiles can range from under 40 GSM to over 3000 GSM which mainly used in landfill end uses.
• Geogrids are usually knitted and PVC coated. Products are designed to be resistant to
  1. Mildew,
  2. Bacteria,
  3. Soil acids (pp) and
  4. Alkalis (pp, pes) and most chemicals.
• Apart from the above, Agro based Geotextiles (woven textiles based on Jute, Coir) are also a niche but growing segment. These have the advantage of being bio-degradable as well as being cheaper.

Application areas

• The principal functions performed by Geotextiles are
  1. Confinement /separation,
  2. Reinforcement,
  3. Filtration and drainage, and
  4. Protection.

• These functions can be described thus:

1. Separation:

• Separation provides a media between the aggregate and the subsoil which absorbs the load in the form of tension and prevents change in alignment of the aggregate.
• Geotextile economically helps the separation concept of keeping two dissimilar materials apart to maximize the physical attributes of each of those materials.
• The object of separation by geotextiles is to prevent a well defined material or rich material from penetrating the sub-grade or the poor soil.
• If the separating media of geotextiles is absent, the infiltration of the sub-grade decreases permeability of the aggregate to the point where it cannot adequately transport the water reaching it.
• Suitable geotextile fabric with good puncture/tear resistance when used as a separator media - eliminates the loss of costly aggregate material into subsoil, prevents upward pumping of subsoil, eliminates contamination and maintains porosity of different levels.
• For separation purposes, both woven / nonwoven geotextiles may be used.

2. Reinforcement:

• The purpose of geotextiles in the reinforcement function is to reinforce the weak sub-grade or subsoil.
• It helps to strengthen the soil surface and to increase the soils ability to stay put especially on the slopes. Due to this the slopes are stabilized either permanently or temporarily and creep stops or at least diminishes.
• Further, it helps in preventing water from permeating a slope and controlling the amount of infiltration that occurs during various rain events.
• Reinforcing aspect of geotextiles can be used for roads, temporary roads, pavements, air strips, stabilized road slopes, retaining walls, containment systems, controlling reflective cracking, fibre or fabric reinforced concrete etc.
• Asphalt impregnated geotextile is used as a paving fabric, relieving stress and acting as moisture barrier. For reinforcement synthetic woven fabric or spun-bond is preferred. Reinforcement is further enhanced by use of geo-grids or geo-nets.

3. Filtration:

• The purpose of geotextiles with reference to drainage and filtration is simply to retain soil while allowing the passage of water.
• When geotextiles are used as drains, the water flow is within the plane of the geotextile itself i.e., they have high lateral permeability.
• At the same time, geotextiles must possess adequate dimensional stability to retain their thickness under pressure.
• The life of pavement of highways/air fields etc is affected by the time for which the water remains under the structural section and its drainage system which is responsible for the removal of free water which is fed directly from the stone base course beneath the structure.
• Needle punched nonwoven is the preferred geotextile for such applications where primary requirement is filtration. Drainage: The use of geotextiles in drainage has made significant strides in changing the conventional procedure of using graded filters.
• Outstanding advantages of geotextiles in drainage are:
  1. It eliminates the filter sand with the dual media backfill.
  2. In some cases, it eliminates the need for perforated pipes.
  3. In situations where only sand backfill is available, it is possible to wrap the drainage pipe with fabric to act as a screening agent. The fabric, thereby, prevents the sand from entering perforation in the pipe.
  4. With Geotextiles, trench excavation is considerably reduced.
  5. Many times the use of geotextiles eliminates the need for trench shoring.
• Needle-punched nonwoven geotextile is preferred where drainage is the primary functional requirement.

4. Protection:

• Lining is used for cushioning and protection of membrane used for applications such as land fill and waste containment from puncture or training by sharp stone or stress.
• Geotextiles can also be impregnated with polymeric or mineral sealing materials such as bentonite clay to provide flexible barriers to mixture.
• Usually spun bond or needle-punched nonwovens are preferred for such applications.
• Each of these functions calls for highly specific textile performance characteristics. As the functional requirements are to be met over many years of the life of the civil construction, durability is often a very key requirement. Many applications require several of the above functions to be met simultaneously.
• Further, the cost of the geotechnical solution is also an important factor to be taken into account in evaluating solutions.

Segment of Geotech:

• The segments of geotech are:
  1. Geogrid,
  2. Geonet and
  3. Geomembrane
  4. Geo-composites
• These are as follows:

1. Geo-grids

• It stands for a speedily emerging division inside the geotextiles area.
• Geogrids not in traditional textile form, it is in polymeric structure form.
• They work as reinforcement materials.
• Coated polyester geogrids have been broadly useful in soil steadiness andgeotechnical reinforcement uses.
• The geogrids are manufactured by extruding high density polyethylene or polypropylene & normally this geogrids are single or multilayer materials.
• The consequential netconstruction possesses large gaps well-known as apertures that increase the interaction with thesoil or aggregate.
• These apertures may vary in size from 1 to even more than 10 cm.

2. Geonets

• They are generally manufactured by uninterrupted extrusion of matching sets of polymeric ribs at acute angles to one another.
• When the ribs are opened, relatively big apertures are formed into a netlike outline.
• Their outline work is mostly appropriate in the drainage region.
• Geo-nets are made of stacked, criss-crossing polymer strands that provide in-plane drainage.
• Nearly all geo-nets are made of polyethylene.
• The molten polymer is extruded through slits in counter-rotating dies, forming a matrix, or “net” of closely spaced “stacked” strands.
• Two layers of strands are called “bi-planar”.
• Three layers are called “tri-planar”.
• Geo-nets are the most recently introduced members of the geo-synthetic family.
• They are grid-like materials, however, distinct, from geo-grids by virtue of their function.
• They do have considerable strength but are used mostly for drainage purposes.

3. Geo-membranes

• They are impermeable membranes, used where the primary function is to have an impervious barrier for fluids.
• However, as the possibility of punctures or tears is high in many areas of use, it is common to protect these membranes by use of Geotextiles.
• Often the geotextiles also perform other functions besides protection of the membrane.
• Geomembranes are made from continuous polymeric sheets that are very flexible, but can also be made by impregnation of geotextile with asphalt or elastomeric sprays or bitumen composites. Geomembranes are used in applications such as liners for water canals, waste canals, solid-waste landfills, covers for solid-waste landfills, waterproofing within tunnels, to control odors in landfills, to prevent infiltration of water in sensitive areas, and beneath asphalt overlays as a waterproofing layer.

4. Geo-composites

• These consist of two or more geosynthetic products put together to increase the combinations ability to optimally address the specific application (say filtration/ reinforcement etc) at minimum cost.
• The best facial appearances of diverse materials are combined in such as way that the benefit/cost ratio is maximized.
• An example of this is known as wick drains in the U.S. and prefabricated vertical drains, in Europe.
• These consist of a 100 mm wide by 5 mm thick polymer cores, for conducting water, with a geotextile acting as a filter and separator socked around the core.

Raw materials used:

• Geotextiles are manufactured from polypropylene, polyester or polyethylene which can be either woven or non-woven.

Technology used:

• Manufacturing process for Woven products includes Weaving / Knitting and Coating (PVC).
• Products can be –
  1. Woven multi-filament,
  2. Woven slit-film monofilament and
  3. Woven slit-film multifilament.
• The non-woven Geotextiles can be made from heat bonding or needle-punching.
• Geogrids are knitted, while Geonets and Geomembranes are extruded from HDPE.