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.
28. THANK YOU
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