geosynthetics and reinforced soil … and reinforced soil structures ... different types of fibres...
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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: [email protected]
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.