GEOSYNTHETICS AND GEOSYNTHETICS AND REINFORCED SOIL STRUCTURES

SUSTAINABLE INFRASTRUCTURE SUSTAINABLE INFRASTRUCTURE DEVELOPMENT & NATURAL

GEOSYNTETICSGEOSYNTETICS

Dr. K. Rajagopal, ProfessorProfessorDept. of Civil EngineeringIIT Madras, Chennai, Indiae-mail: gopalkr@iitm.ac.in

What is sustainabilityLiteral meaning – future generations

should be able to do what we are doingshould be able to do what we are doing today i.e. they should have access to similar natural resources clean air cleansimilar natural resources, clean air, clean water, etc.

This term may also include the aspectsThis term may also include the aspects related to the economic opportunities for rural or tribal peoplerural or tribal people

Geosynthetics & Sustainability

Geosynthetics can help in all aspects of sustainabilitysustainability

Reduces the requirement of natural construction i l lik ilmaterials like aggregate, soil, etc.

Promotes the use of locally available soils

Carbon foot‐print of most highway projects can be reduced by use of geosyntheticsy g y

Natural geosynthetics help in rural employment

Functions of a geotextile layer below road base

Advantage with hi k ithick coir geotextile layer

Letter Symbols for

Different Functions of Geosynthetics

B Barrier (fluid)D DrainageE Surficial Erosion ControlF FiltrationP Protection (of geomembranes)R ReinforcementS Separation

Flexible Break water unit made of  beach sand filled bags in rope net gabionssand filled bags in rope net gabions

Environmental Sustainability of Natural hGeosynthetics

One Hectare of jute plants can absorb about 15 metric tons of CO2 from atmosphere and release 11 metric tons of O2 into the atmosphere during their 100 days of growth

Coir fibres are derived from the husk of t f it b tti tlcoconut fruit by retting process – mostly

performed by semi-skilled manual labour

How long do the natural geosynthetics last in soil?soil?

•4 to 6 years depending on soil environment and type of material (coir jute hessian etc )of material (coir, jute, hessian, etc.)

How long do you need them in soil?g y

•Depends on application

Examples of Limited need

Soil erosion problems: Need protection for 1 or 2 seasonsSoil erosion problems: Need protection for 1 or 2 seasons until vegetation takes root

P lid ti b f 12 t 18 thPre‐consolidation: may be for 12 to 18 months

Different Types of FibresNatural fibres can be of vegetable, animal or mineral origin.

• Vegetable fibres extracted from the fruits of the• Vegetable fibres extracted from the fruits of the plant, are light and hairy (coir, cotton). 

• Bast fibres are found in the stems of the plantBast fibres are found in the stems of the plant providing the plant its strength. Usually they run across the entire length of the stem and are therefore quite long (hemp jutetherefore quite long (hemp, jute, . 

• Leaf fibres extracted from the leaves (pineapple, banana, Palmyra, Sisal)  are generally rather , y , ) g yrough and sturdy .  

Other Types of fibresOther Types of fibres

• Mineral fibres (aspestos)Mineral fibres (aspestos)

• Animal fibres (wool, silk)

Coir Fibre

• Fruit fibre separated from coconut duringFruit fibre separated from coconut during defibreing

• Fibre is extracted from cocunut husk either by• Fibre is extracted from cocunut husk either by retting or by mechanical crushing and decorticatingdecorticating

• Coir fibre has length of 5 to 30 cm and di f 0 2 0 8diameter of 0.2 to 0.8 mm

Indian coir industryIndian coir industry

• Area under cultivation 5,100,000 hectares

• Annual production 12, 600 million nuts (largest in the world)( g )

• Utilization of husk is around 35%

• Production of coir fibre 369 400 MT• Production of coir fibre 369,400 MT

• Employs nearly 590,000 workers (80% are )women)

• Coir is exported to more than 80 countries

Basic composition of Lignocellulosic Fibres

Production of Coir fibre from coconut fruitcoconut fruit

Sarma (2011)

Coir rope nets and textiles

Spinning and weaving to produce coir ropes and netsSpinning and weaving to produce coir ropes and nets

I di l d l dIndigenously developed needle punch machine for coir geotextiles

Sarma (2011)

PVDs made of coir & JuteCoir rope serves as the wick or the drainage mediumCoir or Jute geotextile for the filter surrounding the drain

PVD made of coir

Different coir products

Sarma (2011)( )

Cocologs for erosion controlg

Sarma (2011)Sarma (2011)

Permeable form work for concretePermeable form work for concrete

Enables proper distribution of moisture to fresh concrete during curing processconcrete during curing process

Sarma (2011)

Water absorption capacity of some natural materialsmaterials

Coir: up to almost 100% with 24 hourCoir: up to almost 100% with 24 hourimmersion in water

Jute: 12 to 14%Jute: 12 to 14%

This property helps them provide moisture forThis property helps them provide moisture for the growth of plants in erosion control applicationsapplications

Typical erosion on steep slopesyp p p

Coir mat used for vegetation growth to prevent surface erosion

Large landfill in India lined with coir t t t fi i hmat to promote green finish

Surface characteristics of Natural GeosyntheticsSurface characteristics of Natural Geosynthetics

Very rough compared to the synthetic geosynthetics

Excellent surface interaction with surrounding soils

Higher mobilisation of reinforcement force at lower strains

TEST PROGRAMME

l

gravel

S i 1 Series 2

clay clay

Series - 1 Series - 2

R i f t

clay

gravel Reinforcement layers

clay

Series - 3 Series - 4

y y

Ramakrishna (1997), Rajagopal and Ramakrishna (1998)

60Natural geotextile

40

Polymer coated geotextile

40

)

20

(

20

00 10 20 30 40 50

strain (%)Ramakrishna (1997), Rajagopal and Ramakrishna (1998)

F ti t th f i t tilFatigue strength of coir geotextileRamakrishna (1997)

0 100 200 300 400 500 600ate p essu e ( a)

0H 150H = 150 mm

40

)

80

(

120

Series - 1

Series - 2120Series - 3

Series - 4160

Series 4

comparison of performance of various systemsRamakrishna (1997), Rajagopal and Ramakrishna (1998)

0 100 200 300 400p p ( )

0

plate pressure (kPa)

40

80

()

120

clay soil

120

h=100 150 200 250 300 350

160Figure ?. Pressure-settlement response of unreinforced systemPressure‐settlement data of unreinforced systems

Ramakrishna (1997), Rajagopal and Ramakrishna (1998)

0 100 200 300 400 500 600

0

plate pressure (kPa)

40

80

()

120

clay soil

120

h=100 150 200 250 300 350

160

Figure ?. Pressure-settlement response with reinforcement layer at base of aggregate layerData from Series‐III Tests

Ramakrishna (1997), Rajagopal and Ramakrishna (1998)

0 200 400 600 800 1000 1200

0

plate pressure (kPa)

40

80

()

120

clay120

h=100 150 250200 300 350

160

Figure ?. Pressure-settlement response with reinforcement layers at base and mid-depth Test data from Series – 4 tests

Ramakrishna (1997), Rajagopal and Ramakrishna (1998)

RESULTS

Ultimate pressure on clay bed = 20 kPaUltimate pressure on clay bed = 20 kPa

Ultimate pressures (kPa) from plate load testsUltimate pressures (kPa) from plate load testsThickness of

l

unreinforced subbase layer

one layer of reinforcement

two layers oreinforcement

gravel layer (h) 100 mm 100 120 400100 mm 150 200 250

100 200 240 300

120220 250 360

400550 750 900250

300 350

300 370 400

360440 500

9001000 1150350 400 500 1150

Ramakrishna (1997), Rajagopal and Ramakrishna (1998)

Ramakrishna (1997), Rajagopal and Ramakrishna (1998)

SOME OBSERVATIONS

•Coir geotextile at base of gravel layer did not g g yimprove the performance much. Reason is low friction between coir and soft clayy

•However, this base layer will act as a good separator and filter layer in the long runseparator and filter layer in the long run.

•Additional coir geotextile at mid‐depth of gravel resulted in significant improvement. Good interface friction between coir and gravel and hence strength of geotextile is mobilised

Rao and Sreedhar (2012) on the use of coirRao and Sreedhar (2012) on the use of coir geotextiles along with fly ash for pavements

modulus friction factorPolymeric geotextile 52 (kN/m) 0.94

Coir geotextile 16 1.07

Test set-up Rao and Sreedhar (2012)

Bearing Capacity Improvement Ratio at settlement g p y pequal to 5% footing width Rao and Sreedhar (2012)

Bearing capacity improvement ratio at ultimate stateBearing capacity improvement ratio at ultimate stateRao and Sreedhar (2012)

Properties Jute Polyester Polypropylene Specific

Comparison between Jute and other synthetics

Specific gravity 1.48 1.38 0.91

Tenacity, g/d 3 to 5 2 to 9.2 2. to 5.5 B kiBreaking strain % 0.8 to 2 7 to 37 17

Elastic 75 to 85 57 to 99 75 to 95recovery, % 75 to 85 57 to 99 75 to 95

Moisture regain At 12 5 toregain, At 65% R.H. and 27˚C

12.5 to 13.8 0.4 0.01

Effect of heat Does not Sticks at Softens at 143˚Effect of heat Does not melt up to 180˚C

Sticks at 180˚C

Softens at 143 -154˚C

 Sanyal (2011)

Jute FibresJute Fibres

• Fineness and spinnabilitye ess a d sp ab ty• High initial strength• Consistency in tenacityConsistency in tenacity• High rigidity• Good roughnessGood roughness• Low elongation at break• Excellent drapabilityExcellent drapability• Mulch & creating of congenial mico‐climate for plant growthplant growth

Vegetation growth on a highway slope treated with g g g y pjute geotextile

Sanyal (2011)

Sanyal (2011)

Stone column encased in bamboo grid

Dutta et al. (2012)

Bamboo geogrid

100

120/m

)

60

80

forc

e (kN

/

20

40

Tens

ile f

o

0

20

0 0 02 0 04 0 06 0 08 0 1 0 120 0.02 0.04 0.06 0.08 0.1 0.12Strain

Load-strain properties of bamboo gridLoad-strain properties of bamboo grid

Dutta et al. (2012)

0 50 100 150 200 250 300Pressure (kPa)

0

10

2020

30

40ent (

mm)

50

60Settl

eme

70

80

9090only clay

ordinary stone column

Full length polyester geogrid encasement

Full length bamboo encasement Dutta et al. (2012)

0 50 100 150 200 250 300

Pressure (kPa)

0

10

20

30

t (m

m)

40

50

Settl

emen

t

60

70

S

80bamboo encasement of 2 D lengthbamboo encasement of 3.5 D lengthfull length bamboo encasementfull length bamboo encasement

Dutta et al. (2012)

CONCLUSIONS

Geosynthetics can help in sustainability in several ways.

Natural geosynthetics can play an important role in engineered structures.

Moisture holding capacity and surface roughness of natural geosynthetics are highly beneficial properties for g y g y p psuccessful applications.

Natural Geosynthetics can be applied in erosion controlNatural Geosynthetics can be applied in erosion control, drainage, PVDs, etc. Their limited strength can be used in non-critical applications such as in low volume rural roads, pre-consolidation and erosion control works.