Geosynthetics in Flexible Pavements and Carbon Foot Print Analysisand Carbon Foot Print Analysis

Prof. K. RajagopalDepartment of Civil EngineeringDepartment of Civil Engineering, IIT Madras, Chennai, India 600036

f fThis work was part of M.Tech. projects of AvinashUnni, S. Chandramouli, K. Iniyan & Lt.Col. Tushar VigThanks are also d e to Prof A Veeraraga an and DrThanks are also due to Prof. A. Veeraragavan and Dr.Sivakumar Palaniappan

Outline• Field and Laboratory tests performed to

th i fl f ll lassess the influence of geocell layer• Equivalent modulus of the geocell layer q g y

evaluated• Influence on pavement thickness• Influence on pavement thickness

evaluated through stress analysis programsprograms

• Carbon foot print analysis of construction activities

Back ground (GEOCELL)g ( )• Expandable 3-d permeable,

h b b t thoneycomb or web structure,made of strips of polymerIn ented b the US arm corps• Invented by the US army corpsof engineers in the 1970’s toconstruct temporary roads for3D Cellular confinement system        construct temporary roads forheavy military vehicles overweak soils

(GEOCELL)

• Extensively used by US Armyduring the Gulf war for effective

fmoving of militaryvehicles/trucks over the desertsandO iginall de eloped b US sand.Originally developed by US

Army Corps of Engineers (1979)

Simultaneous Mechanisms in 3 DimensionsDimensions

a) Unreinforced soil subjected to shear  a. When pressure is applied on unreinforced weak soils, failure occurs immediately due to lateral flow of soil

b. When surface soil is confined by geocells,b. When surface soil is confined by geocells, failure mechanism is suppressed from formation.

S f t f d tb) Pushing decrease by confinement c. Surface pressures are transferred to deeper strata due to interaction.

c) Lateral stress on cell due to stress with in the cell Ofer and Rajagopal (2008)

Simultaneous Mechanisms in 3 Dimensions

c) Hoop stress development

The three dimensional structure confinesthe infill soil, limiting lateral deformation.Lateral expansion of the infill is restricted by

d) Passive resistance of neighbouring cells

high hoop stress.

) g ge) Interface friction force developed along the cell walls.

Because of all the above phenomena, the pressure transmitted to thefoundation soil reduces.

Trial Construction on an Expansive Clay soil

Trial road section with geocell reinforcement builtgeocell reinforcement built over a length of 200 m

Subgrade Soil at Site

CBR 4%Swell index 150%Swell index 150%Liquid Limit 60%Plastic Limit 25%Plastic Limit 25%

Shrinkage limit 8%

Geocell Reinforced Flexible Pavements

GEOCELL Reinforced Road construction at Govind Dairy Factory

Preparation of ground Stapling to join different geocells

Stretching of the geocell layer

Filling of stone aggregate in geocell Compaction by vibro-roller

Observations on the performance

R i f d tiUnreinforced section Reinforced sectionUnreinforced section

Reinforced section could maintain good level surface

Unreinforced section showed excessive surface depressionsexcessive surface depressions

Road surface was quite uneven Frequent repairs by dumping large Frequent repairs by dumping large

stones

Set Up for Laboratory Model TestsSet Up for Laboratory Model Tests

Soft clay bed prepared in the laboratory

Pressure‐Settlement

Pressure KPa

0

1

0 2 4 6 8 10 12

1

2

tlemen

t cm

3

4

Sett

4

5

6

The Avinash Unni Project Review150 Geocell Sand 150 Geocell GSB 100 Geocell GSB 50 Geocell GSB 100 WMM 50 Geocell Sand 50 Geocell Sand 2

Measured Pressures below geocell layer

The Avinash Unni Project Review

The Avinash Unni Project Review

Laboratory Model Tests

650 mm thick GSB base GSB + Geocell layer filled with sand or GSB

LABORATORY Model TESTS

100 ll d100 mm geocell with sand fill layer 100 mm geocell+sand

100 mm geocell+GSB 150 mm geocell+GSB

Typical results from Plate Load Tests

0 1000 2000 3000

pressure (kPa)

‐10

0

‐30

‐20

m)

‐50

‐40

men

t (m

100 mm Geocell+GSB

‐70

‐60

settl

em

100 ll d

100 mm Geocell+GSB

‐90

‐80100 mm geocell + sand

GSB alone‐100

GSB alone

Analysis of pressure-settlement data

1) KENPAVE (Elastic layer analysis):• Back calculation of modulus of geocell layer based on fieldBack calculation of modulus of geocell layer based on field

plate load test results• Calculation of modulus values of 50 mm,100 mm,150 mm

geocells layers with different in fills based on lab test results• Optimization done by calculating damage ratio and design

liflife

2) PLAXIS 2D Analyses2) PLAXIS 2D Analyses

• Back calculation of modulus of geocell layered pavement section

• Calculation of modulus values of 50 mm,100 mm,150 mm ll l ith diff t i fillgeocells layers with different in fills

Analysis of the Plate Load Test Datay

• E Value for subgrade (CBR 4%)• E- Value for subgrade (CBR 4%) = 10*4 =40 MPa

• E-Value for stabilized subgrade (CBR 6%) g ( )= 17.6*6^0.64 = 55.40 MPa

• E-value for GSB (225 mm thick) = 55400*0 2*225^0 45= 126 8 MPa= 55400*0.2*225^0.45= 126.8 MPa

• E-value for GSB (75mm thick) = 55400*0.2*75^0.45 = 77.3 MPa

• E-value for GSB (150 mm thick) = 55400*0.2*150^0.45 = 105.63 MPa

E l f GSB (400 thi k)• E- value for GSB (400mm thick) = 55400*0.2*400^0.45 = 164.2 MPa

Geocell Reinforced Flexible Pavements

Modulus Improvement FactorsModulus Improvement FactorsType of study MIFType of study MIFField tests 2.75 (150 mm geocell)Laboratory tests 2 92 (150 mm geocell)Laboratory tests 2.92 (150 mm geocell)

2.84 (50 & 100 mm geocell)

Pavement sections were designed using this revised modulus values and different subgrade CBR values

Geocell Reinforced Flexible Pavements

Pavement Thicknesses for 150 msa & 2% CBR

CombinationsIRC-

unreinforcedGeocell at Subgrade

Geocell in base and subgrade

BC 50 mm 50mm 50 mm

DBM 215 mm 185 mm 170 mmDBM 215 mm 185 mm 170 mm

WMM 250 mm 0Geocell with GSB-200

mm

GSB 460 mm 500 mm 100 mm200mm Geocell with soil infill on 200mm Geocell with soil

sub-grade 500 mm300mm

subgrade layerinfill on 300mm subgrade layer

cost (Rs.) / m2 2,635 2,490 2,450

Total thickness 975 mm 735 mm 520 mmDesign Life 16 years 20 years 20 yearsDesign Life 16 years 20 years 20 years

Geocell Reinforced Flexible Pavements

Geocell reinforced dirt track being constructed in a desert

Geocell Reinforced Flexible Pavements 21

Geocell reinforced dirt track being constructed in a desert area

Desert sand being filled in the geocell pockets

Mini-bucket wheel excavator for filling sand in geocell pockets

Heavy army trucks moving easily on the geocell track

Soil details

(Ref: http://maps.google.co.in)

CBR 3%

( p // p g g )

Plasticity index 45%

Swell index 140

Shrinkage limit 8%Shrinkage limit 8%

Section adopted at construction siteSection adopted at construction site

Max damage ratio 0.865

Field Plate Load TestField Plate Load TestTh f ll i t i d f d ti thThe following apparatus were required for conducting the test:

• Circular steel plate of 300 mm diameter and 30 mmCircular steel plate of 300 mm diameter and 30 mm thickness

• Hydraulic jack of capacity 300 kNy j p y• Supporting steel beam of length 5 m• Dial gauges having accuracy of 0.01 mm• Plumb bob• Spirit level• Short steel supporting members• Loaded truck

Compacted SubgradeCompacted Subgrade

1 Test set up Over Subgrade1. Test set up Over Subgrade

Test Result (Subgrade)

Pressure settlement curve for subgrade data

00 500 1000 1500 2000 2500 3000

Pressure (Kpa)

5

10

men

t (m

m)

Test 1Test 2

15

Sett

lem

20

25

2. Plate load test over Granular Subbase

3 Geogrid Reinforcement3. Geogrid Reinforcement

Subbase

Installing flexible and rigid geogridover subgrade

Compaction using rollerCompaction using roller

Set up Over Sub Base (Reinforced with flexible and rigid geogrid)

Pressure Settlement CurvePressure Settlement Curve

00 500 1000 1500 2000 2500 3000

Pressure (Kpa)

0

2

4)

PLAIN GSB Test 1

A GS 26

8

ent (

mm

) PLAIN GSB Test 2

GSB (with flexible GR) Test 1

GSB (with flexible GR) Test 210

12

14

Sett

lem

e

GSB (with rigid GR) Test 1

GSB (with rigid GR) Test 2

14

16

18

Field Density TestsField Density Tests

Field Density TestsField Density Tests

Fi ld d it t t d t d th• Field density tests were conducted over the subgrade and over the GSB (with and without reinforcement)reinforcement)

• Sand replacement method was performed as per• Sand replacement method was performed as per IS2720 PART-28

• For the same compaction efforts, the sub‐base layer compacted over geogrid layer achievedlayer compacted over geogrid layer achieved higher dry density

Data AnalysisData Analysis

KENPAVE (Elastic layered analysis software):

• Back calculation of modulus of Geogridreinforced pavement based on field plate load test results

• Optimization done by calculating damage ratio and design life

Data InputsData  Inputs

Th f ll i t i d f l iThe following parameters required for analysis

• Thickness of layers

• Elastic Modulus

• Poisson's ratio

• Stress and contact area

STEP 1STEP 1

• As per IRC-37 the following formulas used for calculation of modulus of pavement layersp y

Calculation of ModulusCalculation of Modulus

• The applied load in the field test = 150 kNcorresponding settlement=10.47mmp g

Th di f h l 150• The contact radius of the test plate = 150 mm

• Modulus of the Sub base layer was obtained by t i l d d b t hi thtrial and error procedure by matching the measured settlement of 10.47 mm

KENPAVE RESULTKENPAVE RESULTS N E V l f U i f d V ti l Di l tS No E-Value of Unreinforced

layer (MPa)

Vertical Displacement

(mm)

1 65.11 12.49

2 100 10 782 100 10.78

3 105 10.55

4 107 10.47

5 110 10.35

Snapshot from KENPAVESnapshot from KENPAVE

IMPROVEMENT FACTORIMPROVEMENT FACTORI F E ( i f d) / E ( i f d)Improvement Factor = EBC (reinforced) / EBC (unreinforced)

Where E (reinforced) the mod l s of the reinforced base andWhere EBC (reinforced) = the modulus of the reinforced base and EBC (unreinforced) = the modulus of the unreinforced base

• The average value of the plate settlement at an applied load of 150 kN for the flexible reinforcement was 8.06 mm

• Considered the contact radius = 150 mm

• Contact pressure = load/area =150/area of plate = 2140 kPa

Flexible Geogrid ReinforcementFlexible Geogrid ReinforcementImprovement E-Value (Flexible Settlement (mm) p

Factor

(

Geogrid)

MPa

( )

on surface under

150 kN loadMPa 150 kN load

1 107 10 471 107 10.47

1.1 117.7 10.06

1.25 133.75 9.55

1.5 160.5 8.88

1.75 187.25 8.37

1.9 203.3 8.11

1.95 208.65 8.05

Rigid Geogrid ReinforcementRigid Geogrid ReinforcementI t E V l (Fl ibl G id) S ttl t ( )Improvement

Factor

E-Value (Flexible Geogrid)

MPa

Settlement (mm) on

surface under 15T load

1 107 10 471 107 10.47

1.25 133.75 9.55

1 5 160 5 8 881.5 160.5 8.88

1.75 187.25 8.37

2 214 0 7 952 214.0 7.95

2.25 240.75 7.61

2.3 246.1 7.55

The average value of the plate settlement at an applied load of 150 kN for theThe average value of the plate settlement at an applied load of 150 kN for the flexible reinforcement was 7.55 mm.

Layer OptimizationLayer Optimization

id i f d l id d d• Geogrid reinforced layers were considered and the thickness of the various alternate sections were analysed

• Damage ratio should not exceed the designed unreinforced section @ siteunreinforced section @ site

• Most economic and feasible section should be selected

Damage RatioDamage Ratio

Where

Nn

Di

if

Where,

Df is the damage factor, 

N i

f g ,

ni is the actual number of vehicle movements of the ith load dgroup and 

N is the maximum(allowable) number of vehicle movementsNi is the maximum(allowable) number of vehicle movements the structure can support for the ith load group.

Data Inputs

BC DBM WMM GSB

Poisson’s ratio 0.35 0.35 0.4 0.4

Flexible GG 2500 2500 88.94 208.65Flexible GG

reinforced section

E value (MPa)

2500 2500 88.94 208.65

E value (MPa)

Rigid GG reinforced 2500 2500 88.94 246.1

section

E value (MPa)

Cracking ModelCracking Model Th f il it i f ki i i b• The failure criteria for cracking is given by

Nf = f1 (Єr)-f2 (E1)-f

3WhereWhere,

Nf = allowable number of load repetition to preventNf = allowable number of load repetition to prevent fatigue crackingεt =tensile strain at the bottom of asphalt layerεt e s e s e bo o o sp yeE1=Elastic modulus of asphalt layerf1, f 2, f3 are constants1, 2, 3

Here f1 = 0.08060, f2 = 3.89, f3 = 0.8541 2 3

Rutting ModelRutting Model

f (Є ) fNd =f4 (Єc)-f5

Where,Nd = allowable number of load repetition to limitNd allowable number of load repetition to limit permanent deformationε = compressive strain on top of sub gradeεc = compressive strain on top of sub gradef4 and f5 are constants

Here, f4 = 4.1656x10-8, f5 = 4.5337

Optimised sections for different damage ratios (Flexible geogrid)

Optimised sections for different damage ratios (Rigid geogrid)

Reinforced Pavement SectionReinforced Pavement Section

EMISSION CALCULATION

Sustainable ConstructionSustainable ConstructionKey themes of sustainable construction practicesKey themes of sustainable construction practices

• Minimise the energy use in the all phases (production, construction, i d d f lif h )operation and end‐of‐life phases)

• Reduce environmental impacts during the life cycle

• Preserve and enhance bio‐diversity

• Conserve water and land resources

Ad t i ti t i l• Adopt innovative materials

• Reduce  the generation of wastes at all level

Green house gas emissionsGreen house gas emissions

h i h• The primary greenhouse gases are water vapour, carbon dioxide, methane, nitrous oxide, and ozone

• Greenhouse gases usually affect the temperature of the earthtemperature of the earth

• Anthropogenic activities lead to the increase in green house gases 

Need for AssessmentNeed for Assessment

M j it f t di i l f d• Majority of studies mainly focussed upon improving the energy efficiency of structures during the operational phaseduring the operational phase

• The environmental performance of onsite• The environmental performance of onsite construction processes is not currently being measured (Palaniappan et al. 2009)measured (Palaniappan et al. 2009)

• Quantification of carbon emissions from roadQuantification of carbon emissions from road projects is not followed yet

Site layoutSite layout

Ref: http://maps.google.co.in

Material Collection detailsMaterial Collection details

Logistics AssessmentLogistics AssessmentTh t l di id d i t b d• The pavement layers are divided into subgrade, Granular Sub base (GSB), Wet Mix Macadam (WMM) and Hot Mix Asphalt (HMA)p ( )

• Study included y

1. Raw material transportation to the yard, 2. Extraction3. Processing of raw materials4 Onsite operation4. Onsite operation

Data Collection StrategyData Collection Strategy

T l l h 28 kTotal length = 28 kmNo of Chainages = 14 h i k1 chainage = 2 kmPilot Study @ Chainage 34

Data collected for

Material Processing Transportation Onsite Operations

1. Material Transportation

Fuel Consumption details (Transportation)

Total fuel consumption for transportation

T l f l i (Li )

1524111 60 000

1,80,000

Total fuel consumption (Litres)

152411

1259801,20,000

1,40,000

1,60,000

in Litres)

Total fuel consumption (L)

7267480,000

1,00,000

e (Diesel 

36526

20 000

40,000

60,000

Fuel usag

0

20,000

Subgrade GSB WMM HMA

F

2 Material Processing2. Material ProcessingGSB WMM Pl t ( ill t )GSB

Crushing of 50 m3 GSB

(litres)250

WMM Plant (pug mill type)

(Runs using DIESEL GENERATOR)

Processing of 25 m3 WMM 360Crushing of 1 m3 GSB

(litres)5

Total quantity (m3) 28000

( litres) 360

Processing of 1 m3 WMM( litres) 14.4

Total quantity (m ) 28000Fuel consumption (litres) 140000

Total quantity (m3) 56000Fuel consumption (litres) 806400

HMA PLANT

Processing of 10 m3 HMA( litres) 340

Processing of 1 m3 HMA( litres) 34

Total quantity (m3) 19600

Fuel consumption (litres) 666400

Total fuel consumption for material processing

50 %60

Material Processing‐ Fuel Consumption

50 %

41.3 %40

50

ption

20

30

l con

sum

8.6 %10

20

Fue

0GSB WMM HMA

Pavement Layer

3. ON-SITE OPERATION

h d i l d h• The processed materials are transported to the required site location and will be dumped

• The materials will be spread properly using p p p y gmachineries or labours and compacted well to reach the desired density

• Compaction is one of the critical processes in theCompaction is one of the critical processes in the onsite operations (involvement of machineries)

Onsite operation GSB LayerOnsite operation‐ GSB Layer

GSB placement and compaction

F lDuration

f N fTotal

ki F l

Equipment

Fuel efficiency

(LPH)

for chainage 34

(hrs)

No of chainage

s

working time (hrs)

Fuel use (diesel in

litres)B k h 5 660 9240 46200Back hoe 5 660

14

9240 46200Tractor dozer

(D155A) 27 770 10780 291060

d (GD623A1) 11 880 12320 135520grader (GD623A1) 11 880 12320 135520Roller (l&t CASE

459) 4.5 530 7420 33390

Total 506170

Total fuel Consumption- Onsite operationsO it ti

506170

6,00,000Onsite operation

382620

506170

2995303826204,00,000

5,00,000

Fuel261870 299530

2,00,000

3,00,000Fuel

consumption (Litres)

1,00,000

2,00,000

0Subgrade GSB WMM HMA Excavation

Pavement Layer

Total fuel consumptionTotal fuel consumptionT t l f l ti

Transportation

Total fuel consumption

12%

Raw material processing

Onsite activities43%

processing45%

CO Emissions for unreinforced sectionCO2   Emissions for unreinforced sectionTotal consumption from transportation (L) 393597.95

Total consumption from processing(L) 1612800

Total consumption from onsite activities(L) 1557330.32Emission factor (US EPA)(kg of CO2)Emission factor (US EPA)(kg of CO2)

One litre diesel = 2.664 kg CO2 2.664CO2

emission CO2

emission (Kg) (MT)

Transportation 1048544.9 1048.54

Processing 4296499.2 4296.50

Onsite 4148728.16 4148.73Total (for 28

km) 9493.77Total (per

k ) 339 0km) 339.0

Emission for Reinforced SectionEmission for Reinforced Section

• The optimised section designed using the flexible and the rigid geogrid reinforcement g g ghas been taken

• The emissions were calculated for both flexible geogrid reinforced and rigid geogridflexible geogrid reinforced and rigid geogridreinforced pavement section

CO Emissions for reinforced sectionCO2   Emissions for reinforced section

Emissions ComparisonEmissions ComparisonCO i i l K (MT)

339350

400CO2 emission per lane Km (MT)

266 263250

300

350

150

200

50CO2 emission

(MT)

50

100

0Unreinforced section Flexible Geogrid

reinforcementRigid Geogrid reinforcement

Economic AnalysisEconomic Analysis

h l i h b l l d f h• The layer wise cost has been calculated for the designed section without including the profit margin

• The same has been extended to reinforced sectionsection 

• Reduction in construction duration in case of reinforced section is assessed

Cost of different sectionsActual section

Layer Quantity per Unit rate Cost

Flexible Geogrid

Layer Quantity per sq.mUnit rate

(Rs.)Cost

(Rs. per sq.m.)Layer sq.m (m3) (Rs.) (Rs. per sq.m)

Subgrade 0.5 375 187.5

GSB 0.2 1170 234

y Q y p q ( ) ( p q )

Subgrade 0.5 m3 375 187.5GSB 0.15 m3 1170 175.5WMM 0 2 m3 1445 289

WMM 0.4 1445 578

HMA 0.14 9498 1329.72

Sum 2329.22

WMM 0.2 m 1445 289HMA 0.14 m3 9498 1329.72Geogrid 1 No 130 130

Sum 2111.72Miscellaneous 116.4

Total 2445.7Miscellaneous 105.5

Total 2217.3

Rigid Geogridi

Layer Quantity per sq.m (m3)Unit rate (Rs.)

Cost(Rs. per sq.m.)

Subgrade 0.5 m3 375 187.53GSB 0.15 m3 1170 140.4

WMM 0.2 m3 1445 289HMA 0.14 m3 9498 1329.72

Geogrid 1 No 160 160Sum 2106.62

Miscellaneous 105.3Total 2211.9

Schedule analysisSchedule analysis

h b li h d l f hi j i• The baseline schedule of this project is analysed and the time duration for completing each activity is taken for the study (reinforced and unreinforced)

• Duration of the roadwork activities has been• Duration of the roadwork activities has been reduced drastically from the original 883 days to 669 days in case of geogrid reinforcedto 669 days in case of geogrid reinforced pavements

Summary of Resultsy

NATIONAL HIGHWAYNATIONAL HIGHWAYNATIONAL HIGHWAY NATIONAL HIGHWAY 

DEVELOPMENT DEVELOPMENT 

PROJECTPROJECT

Conclusions• The geocell layer increases the structural stiffness• The geocell layer increases the structural stiffness• Thickness of granular layers reduces by as much as

50%50%. • Total cost of the pavement system per unit area is lower

even with the use of expensive geocell layereven with the use of expensive geocell layer.• The long term performance and service life are

increasedincreased• Geocell layer near the surface leads to be best

fperformance.• In case of extremely soft subgrades, additional geocell

l ld b l d t b d l llayer could be placed at subgrade level.• The reduction in thickness of the base layers leads to

f t t ti d l b f t i tfaster construction and lower carbon foot print.Geocell Reinforced Flexible Pavements