A geotextile is defined as any permeable textile material that is used with foundation, soil, rock, earth, etc to increase stability and decrease wind and water erosion. A geotextile may be made of synthetic or natural fibers. In contrast, a geomembrane is a continuous membrane-type liner or barrier Geomembranes must have sufficiently low permeability to control migration of fluid in a constructed project, structure or system. A geotextile is designed to be permeable to allow the flow of fluids through it or in it, and a geomembrane is designed to restrict the fluid flow.

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1. Geotextile
2. INTRODUCTION  Geotextiles are permeable fabrics which, when used in association with soil, have the ability to separate, filter, reinforce, protect, or drain.  Typically made from polypropylene or polyester, geotextile fabrics come in three basic forms: • woven (looks like mail bag sacking) • needle punched (looks like felt) • heat bonded (looks like ironed felt).
3. FUNCTIONS OF GEOTEXTILES  Filtration  Drainage  Separation  Reinforcement  Sealing
4. FILTRATION The equilibrium geotextile to soil system that allows for adequate liquid flow with limited soil loss across the plane of geotextile over a service lifetime.
5. DRAINAGE/TRANSMISSIVITY Ability of thick nonwoven geotextile whose 3-dimensional structure provides an avenue for flow of water through the plane of the geotextile.
6. SEPARATION The introduction of a flexible porous textile placed between dissimilar materials so that the integrity and functioning of both the materials can remain intact or be improved.
7. REINFORCEMENT Geotextile acts as a reinforcing element in a soil mass or in combination with the soil to produce a composite that has improved strength and deformation properties.
8. SEALING • The classic application of a geoxtile as a liquid barrier is paved road rehabilitation. • It minimizes vertical flow of water into the pavement structure.
9. TYPES OF GEOTEXTILES Woven fabrics Non-woven fabrics Knitted fabrics
10. DESIGN PROPERTIES  Puncture Strength  Burst Strength  Dynamic Puncture  Permeability  Apparent Opening Size (AOS)  Grab Tensile Strength and Elongation
11. PUNCTURE STRENGTH  To measure puncture resistance  Stimulates puncture strength to static load of aggregates  Resistance to puncture measured in Newton
12.  Stimulates strength of geotextile to a continuous hydraulic load  Force causing rupture recorded in units of pounds per square inch or kilo Pascal. BURST STRENGTH
13. DYNAMIC PUNCTURE  To measure the strength of geotextile to falling objects.  Stimulates placement of aggregate over geotextile during installation stage.  Expressed in mm.
14. PERMEABILITY  Measures the rate at which liquids can pass through the geotextile  x=k/t x- geotextile permittivity (sec-1) k- geotextile permeability(cm/sec) t- geotextile thickness (mm)  Expressed in liters per square meters per second
15. APPARENT OPENING SIZE (AOS)  Reflects approximate largest opening dimension available through which the soil may pass.  Expressed in mm.
16. GRAB TENSILE STRENGTH AND ELONGATION  Measures tensile strength and elongation along the plane of the geotextile by loading it continually  Value of breaking load expressed in Newton and elongation at break in percent.
17. AREAS OF APPLICATION • Flexible paved road construction • Drainage applications • Pavement overlays
18. FLEXIBLE PAVED ROAD CONSTRUCTION Function of geotextiles: • service life of roads • load carrying capacity • rutting
19. RESEARCHES ON GEOTEXTILE For weak subgrades (CBR=2%)  Service life by a factor of 2.5-3.0  AASHTO structural number by 19% For moderate strength (CBR=4.2-4.5%)  Service life by a factor of 2.0-3.3  AASHTO structural number by 13-22%
20. AASHTO DESIGN METHOD Excellent drainage  SNeff  Drainage factor - 1.20 Poor drainage  SNeff  Drainage factor as 0.60
21. GEOTEXTILE REQUIREMENT Selection of geotextile  Depends on survivability  Governed by anticipated construction stresses
22. PAVEMENT OVERLAYS Benefits of using Fabric Interlayer  Waterproofing of the lower layers  Retarding reflection cracking in the overlay  Increase in structural stability  Absorption of stresses
23. CAPABILITIES OF PAVING FABRICS:-  Reduces permeability of a pavement  Reduces infiltration of moisture  Maintains the strength of subgrade, sub base and base course  Limiting damage due to saturated condition pore pressures
24. PROPERTIES OF PAVING FABRICS  Nonwoven fabrics from grades ranging from 135gm/m² to 200gm/m²  Lighter fabrics are moisture barriers  Heavier fabrics provides cushioning or stress-relieving membrane
25. INSTALLATION PROCEDURE • The surface is cleaned • Cracks are filled or repaired • Tack coat ranging from 1-1.35 l/m² of residual asphalt is evenly applied • The paving fabric is laid with minimum wrinkles • Finally hot mix overlay is placed
26. DRAINAGE • Drainage system should fulfill 2 criteria:- • Have maintained permeability  by providing relatively unimpeded flow of water • Filtration of base soil  by preventing the migration of soil fines into the drain
27. CONCLUSION  Geotextiles are an efficient effective and economic method of solving most of the geotechnical problems in roads.  The design engineer should be well aware of the possible problems and should use this relatively new tool for solving them.  For this he/she should understand properties and capabilities of the geotextile material.

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