Textiles in Civil Engineering (Geotextile)

Granch Berhe2015

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Definition The word ‘Geotextiles’ is a combination of two words. The word ‘Geo’ comes from the Greek word, meaning ‘Earth’, and textiles

“permeable textiles used in conjunction with soil, foundation, rock, earth or any geotechnical engineering-related material”

“Any permeable textile material used for filtration, drainage, separation, reinforcement and stabilisation purposes as an integral part of civil engineering structures of earth, rock or other constructional materials”

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History Geotextiles can be made from either natural or synthetic fibres

The exploitation of the use of natural fibres in construction can be traced back to the fifth and fourth millennia BC as described in the Bible (Exodus chapter 5, verse 6–9)

Babylonians 3000 years ago constructed this Ziggurat using reeds in the form of woven mats and plaited ropes as reinforcements

The Great Wall of China, completed circa 200 BC, utilised tamarisk branches to reinforce mixtures of clay and gravel 3

Any permeable textile natural or synthetic, used with foundation soil, rock, earth, or any other geotechnical engineering related material.

What is a Geotextile?

Geosynthetics are manufactured (not naturally occurring) materials that are used to withstand and/or enhance the forces of the in-place earth.

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Method of production Process Form of fibre Polymer

PP/PE bi-componentContinuous filament PP

Heat-bondedStaple fibre

PPPP/PE mix

NonwovensPP

PETStaple fibre HDPE

Needle-punchedContinuous filament PP

PET

Nonwoven Geotextiles

Needle Punched nonwoven Thermally bonded nonwoven5

Non woven

• More than 75% of the market utilises geotextiles made from various nonwoven fabrics, chiefly staple-fibre needlepunched and continuous-filament spunbonded nonwovens.

• Nonwoven materials are normally 25–30% cheaper than woven materials

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Method of production Process Form of fibre Polymer

Slit-flat tape PP (HDPE)Wide loom (beam) Fibrillated yarn PP

Wide loom (creel) Multi-filament yarn PET (PA)Woven

<3.8m loom (beam) Medium mono filament with yarn PP

HDPEPA

Woven Geotextiles

film tape extruded tape PET multifilamentMonofil7

Woven • They have a surprisingly wide range of applications and

they are used in lighter weight form as soil separators, filters and erosion control textiles.

• In heavy weights, they are used for soil reinforcement in steep embankments and vertical soil walls; the heavier weight products also tend to be used for the support of embankments built over soft soils

• Advantage - stress can be absorbed by the warp and weft yarns and hence by fibres, without much mechanical elongation

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Method of production Process Form of fibre Polymer

Stitched-bonded Nonwoven base with multi-filament stitch yarn

PP or PET nonwoven PET stitching

Knitted Weft insertion filament yarn PET

Warp knitted Multi-filament yarn PET

Knitted Geotextiles

Knitted base Upper surface 9

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The mode of operation of a geotextile in any application can be defined by the following functions:

Functions of Geotextile :

Separator Reinforcement Drainage

Filter Energy absorberContainer

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Functions of geotextiles

Filtration – liching of water Drainage - collects and redirects liquid or gas

Separation – layer between fine soil and coarse material

Reinforcement - when the stability of the weak subgrade or soil is complemented by higher tensile strength of fabric.

Container - when it holds or protects the materials such as sand, rocks, fresh concrete12

Applications 1. River bank protection.2. Seabed protection.3. Sea coastal protection.4. Coastal protection/sea defences.5. Drainage.6. Perpendicular versus in-plane water flow applications.7. Reservoirs and lakes.8. Concrete mattresses.9. Vertical screens.10. Geobags.

11. Reclaimed land.12. Anchoring.13. Paved and unpaved road subgrade separation.14. Embankments.15. Reinforced earth.16. Reflective cracking.17. Railways.18. Landfills.19. Slit fences.

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Applications of Geotextile :

Reservoirs, damsReservoirs, dams

Liquid wasteLiquid waste Solid wasteSolid waste

RoadsRoads RailroadsRailroads

Erosion protectionErosion protection

Retaining wallsRetaining walls

Drainage systemsDrainage systems

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1. Physical properties:a) specific gravityb) weightc) thicknessd) stiffnesse) density .

2. Mechanical properties:a) tenacityb) tensile strengthc) bursting strengthd) drapabilitye) compatibilityf) flexibilityg) tearing strengthh) frictional resistance

3. Hydraulic properties:a) porosityb) permeabilityc) permittivityd) transitivitye) turbidity /soil retentionf) filtration length etc. 16

4. Degradation properties:a) biodegradationb) hydrolytic degradationc) photo degradationd) chemical degradatione) mechanical degradationf) other degradation occurring due to attack ofrodent, termite etc.

5. Endurance properties:a) elongationb) abrasion resistancec) clogging length and flow etc.

Performance Requirements of Geotextile

Properties • mechanical responses,

– ability of a textile to perform work in a stressed environment and its ability to resist damage in an arduous environment

– The ability to perform work is fundamentally governed by the stiffness of the textile in tension and its ability to resist creep failure under any given load condition

• filtration ability – function is to hold intact a freshly prepared soil surface, so that water may

exude from the soil surface and through the textile without breaking down that surface

• chemical resistance– use of textiles in contact with highly acidic peat soils, where in tropical

countries, pH values down to 2 have been encountered– Industrialised countries– Ultraviolet light

They are all developed from the combination of the physical form of the polymer fibres, their textile construction and the polymer chemical characteristics

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Fibers usedNatural fibres offer high strength, high modulus, low breaking extension and low elasticity.

Some of the plant fibres that can be used in geotextile manufacture are jute, sisal, flax, hemp, abaca, ramie and coir

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Advantages of natural fibers

• low cost, • robustness, • strength/durability, • availability, • good drapeability • biodegradability/

environment friendly

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Synthetic • Synthetic fibres are the main raw materials for

the manufacture of all types of geotextiles– polypropylene, polyester, polyamide and polyethylene

• polyester widely used– exhibits superior creep resistance and tenacity values – is almost inevitably used when high strengths are

required– applications where the geotextile is subjected to high

stresses and elevated temperatures– susceptibility to hydrolytic degradation in soils

exceeding pH 10.

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• PP– low cost, acceptable tensile properties and

chemical inertness– disadvantages of polypropylene are its sensitivity

to ultraviolet (UV) radiation and high temperature and poor creep and mineral oil resistance

• PA– cost and overall performance render it inferior to

polyester.

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Limitations of synthetic

• Synthetic geotextiles can cost over 10 times as much per unit area as natural ones

• non-biodegradable and may cause soil pollution

• The material composition of geotextiles determines their longevity in the field: natural products last about two to five years, whereas synthetic products last >25 years

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• Erosion control geotextiles are made from natural (jute, coir, sisal, cereal straw and palm leaves) or synthetic (nylon, polypropylene, polyester and polyethylene) materials

• Geotextiles are used for separation of two distinct ground layers, slope stabilization, vegetation management and soil erosion control.

• Geotextiles are widely used to control on-site and off-site soil erosion of human-disturbed lands

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PET Vs PP in Geotextile Applications

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Property PET PP

g/cm3 1.38 0.91- 0.93

Melting Point 265 165

Strain 10 -15 > 100 %

Creep < 2% 5%

Modulus (Gpa) 10 2.8

Breaking Elongation 20-50 % 40 -70 %

Breaking Tenacity (gm/d)

9 6

UV Resistant High Susceptible

Polar solvents Degrade Resistant

pH > 9.5 Hydrolysis

3 -13

Moisture Regain 0.4 0

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Polypropylene Polymer has distinct advantages 1. Resistant to chemical attack2. Stable to pH between 3 and 133. Non-biodegradable4. Resistant to soil-bound chemicals, landfill leaches, mildew and

insects.5. Lightest fibre

Polyethylene Terephthalate (PET) Polymer has :1. Superior Breaking Tenacity (Strength)2. Superior creep characteristics required in some critical

reinforcement materials.

PET must not be used in contact with soils with pH >9.5 For PET made Geotextiles hydrolytic resistance is required to be

observed. For Geotextile application in case of PP Oxidative resistance is

required to be observed.

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Temperature resistancePET is winning with a melting point of 265oC versus the 165oC of PP. This means that for applications which need temperature resistance e.g. resistance to reflective cracking in roads, PET is preferable. Creep PET by far the best choice. Chemical resistance Generally PP is better. PP is preferred for landfills. Alkali resistanceAgain PP is the better choice e.g. in touch with fresh concrete. UV resistance This is a PET domain. PP geotextiles should be improved with carbon black for a better behavior to UV.

Technical Requirement for use in subsurface drains

• Breaking load not less than 10 kN/m • Minimum Failure strain of 10%• Apparent opening size 0.22mm – 0.43 as soil properties• Allow water flow @ not less than 10lit/sqm/sec• Minimum puncture resistance of 200 N• Minimum tear resistance of 150N

PET is Preferable Than PP

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Technical Requirement for use in Highway Pavement

• Minimum Tensile strength 36.3 Kg• Elongation 50%• Asphalt Retention 10 kg/10sqm• Melting Point 150C• Surface Texture- heat Bonded on one side only

PP is Preferable Than PET

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Technical Requirement for use in Protection Works

• Aperture : Rectangular, square or oval • Colour : Black• Strength : Min 10kN/m• Elongation: Max 15%• Life : Min 8 years

PET is Preferable Than PP

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Silt Fence• Prevents storm water from transporting sediment off-site

• Alternate for hay bales• Low elongation (stretch)

important for more support • Filtration and tensile

strength properties most important

• Commonly light weight woven (higher strength) geotextiles

PET is Preferable Than PP

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Roadway Separation / Stabilization

• Prevents subgrade from intermixing with base course

• Alternate to undercutting

• Low elongation for higher modulus

PET is Preferable Than PP

PP is Preferable Than PET if pH is >9.533

PET is Preferable Than PP34

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Geotextiles in Drainage

Geotextile around pipe

Geotextile lining trench

Lining pipes not preferred method

PP is Preferable Than PET

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Filtration

w/ geotextile

w/o geotextile - loss of fines

PP is Preferable Than PET

Avoid granular material penetration Puncture resistance

PP is Preferable Than PET

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Thank You!

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