geosynthetics- polymeric planar product

8/18/2019 Geosynthetics- polymeric planar product

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ABSTRACT

Geosynthetics are polymeric planar product used with soil, rock or any other geotechnically

related material as an integral part of a manmade project. A common generic name

geosynthetics is being used to refer the different materials. The function of geosynthetics is

separation, reinforcement, and drainage, moisture barriers etc.This paper outlines the use of

geosynthetics in highway engineering


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INTRODUCTION

Application area of geosynthetics range from ocean bed to roadbed ,from foundation

on soft soils to land slide control and from waste disposal sites to water reservoirs. These

have become an integral part of the solutions to many civil engineering problems. Most

common use of geosynthetics in highway engineering especially for road constructed in weak

sub grade where it increases stability and improves performance by separating the aggregatefrom the sub grade, in use of highway embankment construction where in marginal material

are used, in pavement edge drains, embankment slope protection and in hill slope protection

to control damage to the hill roads .In these situations inclusion of geosynthetics like

geotetiles or geogrid can lead to less deformation of road and can reduce the re!uired

thickness of the base material. Geosynthetics based solutions results in overall saving in cost

and natural materials leading to environmental and natural resources protection.

Geosynthetics can be used in temporary or permanent roads, new road construction,

rehabilitation of eisting roads etc. There are three levels at which geosynthetics can be

introduced

i. At the interface of sub"grade and sub"base

ii. At the interface of sub"base and base

iii. In the overlay

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The development of geosynthetics in past three to four decades has provided the

strategies for enhancing the overall performance of the paved roadways

The geosynthetic layer or geogrid layer ,installed at the subgrade level allows

construction e!uipment access to weak subgrade soil sites, and makes its possible to achieve

proper compaction of the first few lifts of granular soils. $uring the operating life the

geosyntheticlayer improves the overall performance of the paved roadway by performing its

drainage and filtration functions.

In case of marshy land or road built on lower embankment. the road undergoes

differential settlement depending on the depth of marine clay .In this case Geobo along with

geonet can be used.

Geosynthetics can be used effectively during the initial construction of a new road or

for providing remedial measures to a road subjected to distress.

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1.0 WHAT ARE GEOSYNTHETICS ?

Geosynthetics are defined as, civil engineering materials that are synthesi&ed for used

with geological material like soil, rock or any other geotechnical engineering related material

to improve or modify its behaviour.

2.0 VARIOUS PRODUCTS COVERED UNDER GEOSYNTHETICS

Geosynthetics are sub divided into two categories , based upon their method of

manufacture

'ynthetic fabrics

(atural fabrics

#.) '*(T+TI- A/0I-'

ollowing are the specific products in the synthetic fabric family .ach products has its

distinct application and benefits.

i. Geotetiles

ii. Geogrids

iii. Geomembranes

iv. Geocomposites

v. Geonets and other products,geomats,geomeshes,geowebs.

Geotextiles

These are permeable tetile materials and may be woven, non"woven or knitted

Wovens

As their name indicates, they are manufactured adopting techni!ue similar to weave

clothing tetiles. this type has the characteristic appearance of two sets of parallel threads or

yarns. the yarn running along the length is known as a warp and the one perpendicular to it is

known as waft.

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Non -Wovens

(on" woven geosynthetic can be manufactured from either short staple fibre or

continous filament yarn .the fibres can be bonded together by adopting thermal ,chemical or

mechanical techni!ues or a combination of techni!ues.the thermally bonded non"wovens arerelatively thin with a typical thickness of about 2.3 4 )mm .mechanically bonded non wovens

have a typical thickness in the range of # to 3mm. fig illustrates a thermally bonded non 4

woven geosynthetics.

The significant difference between wovens and non wovens is that the polymer

filaments are aligned in the direction of the warp and waft in the weaving process of the

wovens.

Knitted

5nitted geosynthetics are manufactured by knitting. In this process interlocking a

series of loops of yarn together is made. All of the knitted geosynthetics are formed by using

the knitting techni!ue in conjunction with some other method of geosynthetic manufacture,

such as weaving.

Geo!i"

It is a planar structure formed by a regular network of tensile elements with apertures of

sufficient si&e to allow interlocking with surrounding soil, rock or earth. they are also

characteri&ed by high dimensional stability, high strength and high tensile modulus at very

low elongation. They are two varieties, uniaially oriented6mon oriented and biaially

oriented6bioriented7, with enhanced strength in one or both the directions .They are primarily

used for soil reinforcement. ig shows the geogrids.

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ig. ) Geogrids

a7 8niaially oriented 6mono"oriented7 6b7 /iaially oriented 6bi"9riented7

Geo#e#$!%&es

Geomembranes are thin two dimensional sheets of materials with a very low

permeability. These are fleible materials and can be strengthened with a fabric or

film.geomembranes are only subject to a small amount of seepage as a result of permeation.

or all practical purposes they may be considered to be impermeable to both gases and fluids.

Thus they are suitable for forming waterproof or gas proof barriers between adjacent bodies

of soil or soil and fluids.

Geo'o#(osites

Geocomposites are produced from the combination of two or more geosynthetics.

The composites have better properties to meet the needs of a special application . for eample

a combination of woven and non woven geosynthetics are used for soil reinforcement or as

separator depending on which one is used as a prime constituent. Geocomposites are useful

as a separator in difficult and dynamic load conditions. $ifferent forms of geocomposites

are : non"woven sheet and net composites , woven sheet and net core composites , non"

woven and mat composites.

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2.2 NATURA) *ABRIC

Geomats and Geowebs

These may be course woven or joints obtained by partial melting made of strips,

rigid filaments or etracted strands. They are generally fleible and junctions of overlapping

strands not firmly connected. They can be synthetic or natural .These are also three"

dimensional mattresses dimensional commonly used in erosion control as well as staple

fibres, continuous filaments or micro grids used as admiture to strengthen soil. ig shows

the geomats.

ig.# Geomats 6a7 -oir matting 6b7


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=. -hlorinated polyethylene

Polyamide

There are two important types of poly amide.the first one is aliphatic polyamide

obtained by polymeri&ation of petroleum derivative. The other type is also an aliphatic

polyamide. it is obtained by the polymeri&ation of salt of adipic acid and

heamethylenediamine

polyester.

It is made by polymeri&ing ethylene glycol with dimethylterephthalate.all these

materials are derivatives of petroleum.

Polyethylene

The main group of polyethylene are

>$? 6low density polyethylene7

>>$? 6linear low density polyethylene7

+$? 6high density polyethylene7

Polypropylene

?olypropylene is a crystalline thermoplastic produced by polymeri&ing propylene

monomer in the presence of stereo specific catalyst system.they are mainly two types

homopolymers and copolymers

Polyvinylchloride

?olyvinyl chloride is mainly used in Geomembranes and as a thermoplastic coating

material .the basic raw material for the production of a pvc is vinylc-lo!i"e

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Ethylenecopolymer bitumen

thylene copolymer bitumen membranes have been used in civil engineering works

as sealing material. They are used as seal in connection with resistance with hydrocarbons,

acids and alkalies.

Chlorinated polyethylene

The properties of polyethylene depends on the !uality of the ? and the degree of

chlorination

Table ): -omparative properties of four polymers

polyester polyamide polypropylene polyethylene

strength + M > >

lastic modulus + M > >

'train at failure M M + +

creep > M + +

8nit weight + M > >

cost + M > >

8 light stabili&ed + M + +

unstabili&ed + M M >

Alkalies > + + +ungus,vermine M M M +

fuel M M > >

detergents + + + +

H:High M:Medium :o!

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.0 APP)ICATION IN HIGHWAY ENGINEERING

.1 se(%!%tio&

'eparation function refers to the separation of two dissimilar soils materials .The

primary geosynthetic function is to prevent intermiing of two different materials throughout

the design life of the structure. ehicle load application cause sub grade soils to migrate into

the aggregate base of the pavement section .-ontamination of the aggregate base by the

subgrade results in the reduction of the effective base thickness to less than that which was

part of the original design, resulting in decrease in the load carrying capability of the

aggregate base and a reduction in pavement life. Geotetiles prevent the sub"grade material

from migrating into the aggregate base, thus increasing pavement life. ig shows the

separation function of geosynthetics.

ig.% Se(%!%tio& function of geosynthetics

.2 *ilt!%tio&

The filtration function has two concurrent objectives. These are to retain the particles

of the filtered soil while permitting water to pass through the plane of the geotetiles from

the filtered soil .Application of this function includes highway edge drains, retaining wall

drainage system and land fill leachate collection system. The Geotetile and adjacent soil filter &one together control ultimate flow capacity of the

system. The Geotetile plays an important role in developing the filter &one, which most

significantly controls the water flow .The permittivity of a geotetile soil filter system

remains much higher than the permeability of the neighbourhood soil even after considerable

time.

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ig 1.iltration functions of Geosynthetics.

.+ D!%i&%e

Geotetiles have replaced grades soil fillers for drainage of virtually all including ground

water intercept 'ystems, pavements, building foundations dams and walls.

If the subgrade soil is subjected to persistent or even occasional wet conditions, the

geotetiles placed over it must be highly permeable to allow rapid drainage of water from the

loaded subgrade soil up into the free draining aggregate base .otherwise ,under the rapid

loading conditions from traffic ,water pressures in the soil can fail the subgrade by soil

li!uification.

Geotetiles provide this critical permeability as they filter or keep the fines from

migrating upward into the aggregate. Maintaining drainage of the aggregate base and

subgradesoil is very important to prevent accelerated failure of the support system

$rainage function of geotetiles

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. Rei&/o!'e#e&t

The strain or deformation in any direction could be controlled by introducing the

reinforcement 6geosynthetic7 by way of frictional forces acting against deformation .

Geotetiles are used in reinforcement through mechanisms of restraint or confinement,friction, membrane effect and local reinforcement. The reinforcement function of a

geotetiles comes into effect when the subgrade soil is weak. the reinforcement function

effective in stronger soils when designing for very heavy wheel loads.

ig.3 Tensioned Membrane function of geosynthetics.

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Table ) shows functions of geosynthetics

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PROPERTIES O* GEOSYNTHETICS

The properties of geosynthetics can be grouped under the following categories,

i. material and fibre properties

ii. geometrical aspects

iii. mechanical properties

iv. hydraulic properties

v. durability or chemical properties

Material and fibre properties

Temperature water content of the materials of geosynthetics are the two aspects

which affect the various properties of geosynthetics. The fibre used in the manufacture of

geosynthetics are built up from linear macromolecules, whose properties are based on the

bonding forces between the atoms and structure in which the macromolecules are arranged.

Geometrical aspects

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The choice of particular type and construction depends on the properties re!uired.

Eidth and length, thickness, mass per unit area and available prefabrication techni!ues all

play a role in the definite choice of geosynthetics and construction. $epending on the mass

per unit area the length vary from 32 to #22m.the thickness lies between 2.#to )2mm.the

mass per unit area of non"Eovens and woven are of the range )22to)222 gCm# and )22 to

#222gCm# respectively.

Mechanical properties

Mechanicalproperties are the load deformation characteristics of geosynthetics.

The mechanical properties of geosynthetics depends on the mechanical property of the fibre

structure, fibre material, the yarn structure and structure of the geosynthetics.the effective performance of geosynthetics in civil engineering applications, depends on the tensile stress"

strain characteristics of the soil geosynthetics interface friction behaviour.

The important mechanical properties are,

i. interface friction

ii. fatigue resistance

iii. creep resistance

iv. tear"strenght

v. abrasion resistance

vi. puncture strength

Hydraulic properties

Geosynthetics are used as filters in bank protection works, downward culverts and in bed

protection works along canals.geosynthetic used in road construction are installed in the

substructure or as a layer separating the substructure from the subsoil .in all these fields

geosynthetics must satisfy re!uirements for water permeability and soil tightness. it will

fulfill the two important conditions,

• It should provide ade!uate conductivity to allow the free flow of water out of the

surrounding soil into the drain.

• It should prevent particle movement from the parent soil into the drainage media.

Durability

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Abrasion resistance and ultra violet resistance are the other two factors which

affect the durability of geosynthetics.

"brasion resistance

Geosynthetic subjected to abrasion in many ways. Abrasion could occur as a

result of friction produced by movement of rock and soil against the surface of the

fabric such as wave action or the aggregate cover in fabric reinforcement application

such as roadways and railways.

#ltra $iolet %esistance

In order to minimi&e 8 degradation, geosynthetics in most applications is

embedded in soil. $uring the manufacturing process additives such as carbon black

or 8 stabili&er are added to increase their 8 resistance.

.0 HOW TO INSTA)) GEOTETI)ES?

The successful use of geotetiles in soil stabili&ation re!uires proper

installation. The four basic steps involved in placing of geotetiles.

'ubgrade preparation

Geotetiles placement

Aggregate placement

Aggregate compaction

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ig.; installation of geotetiles

-areful planning and preparation for each installation step speeds construction and

insures good performance and full benefit from non woven geotetiles. The site should first be cleared of all sharp objects, tree stumps and large stones.The aggregate selected should be

compactable and non moisture sensitive.

The geotetiles is laid in the direction of construction traffic. Geotetiles panels should

be overlapped both side to side and end to end from ).3feet to % feet, depending on the

subgrade strength.

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Adjacent fabric edges can be sewn in the field with a portable sewing machine

powered by a generator. Two laborers are easily handling a roll of non woven

geotetilefabric. 9n very soft subgrades ,the fabric layout and aggregate placement should be

begin on the firmst soil on the site perimeter , from there the fabric can be rolled onto softer

sections. Trucks back dump aggregate onto the fabric, tracked bulldo&er spread the

aggregate.

9ver very soft subgrade, care must be taken during aggregate placement to insure

the fabric is not moved out of position nor the subgrade overstressed. ehicle should not be

allowed to drive directly on the fabric. The surface is initially compacted by walking the

tracked bulldo&er back and forth over the aggregate while waiting for the net aggregate

load. inal compaction is achieved with a vibratory compactor.

inal pavement construction should be delayed as long as possible to monitor the

unpaved aggregate sectionFs performance. After these steps are completed, the road is ready

for use .stability will increase as traffic and the confining action of the fabric continue to

densify the aggregate and consolidate the subgrade.

3.0 GEOTETI)E WORTH THEIR COST IN AGGREGATE

Eith a good design and proper installation, more projects reali&e a %2 percent to 12 percent drop in re!uired aggregate thickness. This leads to drops in production costs because

the non"woven geotetiles only costs a fraction of that saved from the reduction in re!uired

aggregate. The geotetiles usually more than # inches to % inches of compacted, in place

aggregate , but can save several inches of aggregate. the separate function is more dramatic

over weak subgrade soils, but is economically practical in the long run to use even on more

competent sub grades.

Geotetiles are recommended for this separation function because of their low cost.

one etra benefit of using a geotetiles for separation is that almost all the aggregate over the

geotetiles can be reclaimed and reused.

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4.0 GEOSYNTHETICS IN ROAD CONSTRUCTON

Geosynthetics are being etensively used in road and airport fleible pavements and

overlays. In unpaved roads 6having no black top7 introducing a very thin non"woven

geotetiles is found to be advantage for soft sub grades primarily through separation and partially through reinforcement. In overlays introduction of geogrid effectively reduces

reflection cracking. Geogrids at the subgrade"subbase interface or at base"sub base interface

or at the base"surface course interface could also improve the pavement behaviour by

reducing cracking and rutting.A geomembrane ecapsulated layer can control moisture

migration in epansive soils. +eavy"duty geocomposites can be put to use in strategic

locations when heavy vehicles can directly move over them. Geosynthetics are thus a great

form for ease in construction over soft soils as well as for long 4term performance of road

pavements.

5.0 USE O* GEOTETI)ES IN ROAD ON SO*T SUBGRADES

>arge sections of our road network happen to be routed over areas containing soft

clays, alluvial soils organic soils and massive clays under waterlogged conditions. 0oad built

in such soft and epensive soil sub grades suffer from many problems and deteriorate early

investigations on the failure of such roads reveal that one of the major cause of failure could

be attributed to the presence of the fine grained soils intermi with aggregate base The

principal function of .

Geotetiles is to separate aggregate from the sub grade.This separation and

confinement plus additional strength gained by frictional interlock between the aggregate and

fabric, helps to reduce the stress on the subgrade, thereby increasing load bearing capacity of

structural section as well as sub grade layers. additional benefits are desired when the

geotetiles provides secondary functions of filtration and drainage, allowing ecess pore

water pressure to dissipate into side drains.

$uring the construction of the road pavement, the maimum drainage to the fabric

occurs due to construction stresses and not due to traffic loads. Therefore, the geotetiles

selected should meet the minimum physical standards the road performance observations

have also been ade!uate to establish that the geosynthetics are an effective substitute for

convensional blanket courses.

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Its use become very cost effective when good !uality sub base materials are not

available within economic lead, when -/0 of subgrade is low, when roads are water logged

and when the roads are to be constructed speedily and maintained.

/ased on field observations, it can be concluded that non woven geotetiles have got an

edge over the woven fabric due to their high percentage elongation as well as better filtration

characteristics. +owever, a woven geotetiles can also be used of the subgrade condition is

fairly dry and the fabric is able to withstand construction stresses. It is also recommended

that while using crushed stone metal for construction of pavements. A 3 to )2 cm thick

cushioning layer is provided over the geotetile layer, for better performance of the fabric

layer.

10.0 BENE*ITS

• 0educing the intensity of stress on the sub grade.

• ?reventing sub grade fines migrating up into the base.

• ?reventing contamination of base materials.

• 0educing the depth of ecavation re!uired for the removal of unsuitable sub grade

materials.

• 0educe the thickness of aggregate.

• 0educing differential settlement of the roadway.

• 0educing maintenance and etending the life of the pavement.

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11.0 CASE STUDY

in India the important highway projects being eecuted in the present time are the

Golden Huadrilateral connecting $elhi"Mumbai"-hennai"5olkatta"$elhi with atotal length

of 3@1; km, and (orth"'outh and ast"Eest corridors connecting 'rinagar to 5anyakumari

and 'ilcher to ?orbandar with a length of about =%22km.Geosynthetic layers are being used

in these projects at subgrade level. The subgrade has been provided a cross slope of #.3

prior to placement of the geotetile layer. The order of these layers starting from bottom is as

follows: granular sub base course"32cm thick, wet mi macadam"#3cm thick, dense

bituminous macadam")Bcmtk,and bituminous concrete"3 cm thick . A portion of the road

way was completed in ebruary #22% and opened for the traffic. Its performance been found

very satisfactory in the past 3 years.

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CONC)USION

/efore the geosynthetic can be put to effective use, their characteri&ation is of atmost

important. The use of geosynthetics in unpaved roads reduces the permanenet deformation

and increases the modulus of resilience significantly. Geogrid reinforcement results in

retardation of reflection cracks in overlays. Thus selection of the right geosynthetic in a

specific job should take into consideration the aggregate, sub"grade and epected loading.

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BIB)IOGRAPHY

). $r 'anjaykumar shukla, Jgeosynthetic at subgrade level in paved roadways

design practice and installationK, J-ivil ngineering and -onstructionK

March #22;

#. G.> 'ivakumar /abu, Jsoil reinforcement and geosyntheticsK

%. $r. ?. ?urushothamaraj, JGround improvement techni!uesK1. http:CCwww.geofabrics.com

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geosynthetics- polymeric planar product

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