Lab Scale Studies on Pore Clogging Nature of Flyash Mixed Soil With Various

8/8/2019 Lab Scale Studies on Pore Clogging Nature of Flyash Mixed Soil With Various

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INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING

Volume 1, No 1, 2010

Copyright 2010 All rights reserved Integrated Publishing services

Research Article ISSN 0976 4399

50

Lab Scale Studies on Pore Clogging Nature of Flyash Mixed Soil With Various

Geotextiles- A Study on Soils from Dindigul District

R.Gobinath1, K.Rajeshkumar2N.Mahendran3

1- Lecturer 2- Lecturer 3- Professor and Head

Department of Civil Engineering,PSNA College of Engineering and Technology, Dindigul

Email: [email protected]

ABSTRACT

Geotextiles are increasingly being used in transportation applications due their ease of

construction and economy over traditional methods. Geotextiles are often used in embankmentconstructions their two most important roles being the reinforcement of the foundation and

separation of the embankment fill from the foundation soil. In addition to these roles, geotextiles provide lateral drainage of percolation water and prevent the build-up of excess pore water

pressure. The current design of GC drains and geotextile drains is primarily dependent on theirflow rate capacities. However, the hydraulic compatibility of a geotextile with the contact soil is

an important issue and should be considered in design procedures. This compatibility is usuallyanalyzed through laboratory soil filtration tests. The first main requirement for ensuring this

hydraulic compatibility is that the drain should not be clogged throughout the life of the structure.The second requirement is that the soil piped through the geotextile should be minimal, so that

the internal stability and modulus of the soil are not adversely affected. reported excessive

clogging of GC drains in two different projects. The drain was completely clogged due toaccumulation of soil fines at the surface and inside the geotextile (blinding and clogging

phenomenon, respectively), resulting in excess pore water pressure build-up under the pavement.

Similar problems, excessive clogging of geotextile component of GC drains with fine-grainedsoils, were also reported by. These failures indicate that the hydraulic compatibility of contact

soil with the geotextile component of a drain is an important issue, requiring considerationduring pavement drainage system design. The problem of fine particle clogging becomes more

cumbersome when industrial by-products are in contact with geotextiles in pavement drainagesystems. The nature of these geomaterials is different than regular soils, often consisting of

significant amounts of fines. The existing geotextile selection criteria may not be directlyapplicable to these materials and, in most cases, their filtration or drainage performance with

geotextiles should be investigated by conducting laboratory tests. In this study Geosyntheticswas tested with varying fly ash content with soil samples taken from Dindigul district and their

hydraulic conductivity is measured to check the viability of using Geosynthetics for highwaysproject carrying clayey soils.

Keywords: Geotextiles, Fly ash, Clogging, Pore size distribution.


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1 Introduction

Geotextiles are increasingly being used in transportation applications due their ease of

construction and economy over traditional methods. Geotextiles are often used in embankmentconstructions their two most important roles being the reinforcement of the foundation and

separation of the embankment fill from the foundation soil. In addition to these roles, geotextiles provide lateral drainage of percolation water and prevent the build-up of excess pore water

pressure. Pavement subsurface and highway edge drainage systems are other application areas inwhich geocomposite (GC) drains are commonly employed. GC drains are composed of a geonet

sandwiched between two geotextile layers, and have been cost effective alternatives overtraditional drainage systems for the last two decades

The current design of GC drains and geotextile drains is primarily dependent on their

flow rate capacities. However, the hydraulic compatibility of a geotextile with the contact soil isan important issue and should be considered in design procedures. This compatibility is usually

analyzed through laboratory soil filtration tests. The first main requirement for ensuring thishydraulic compatibility is that the drain should not be clogged throughout the life of the structure.

The second requirement is that the soil piped through the geotextile should be minimal,

so that the internal stability and modulus of the soil are not adversely affected. reported excessiveclogging of GC drains in two different projects. The drain was completely clogged due to

accumulation of soil fines at the surface and inside the geotextile (blinding and cloggingphenomenon, respectively), resulting in excess pore water pressure build-up under the pavement.

Similar problems, excessive clogging of geotextile component of GC drains with fine-grainedsoils, were also reported by. These failures indicate that the hydraulic compatibility of contact

soil with the geotextile component of a drain is an important issue, requiring considerationduring pavement drainage system design.

The problem of fine particle clogging becomes more cumbersome when industrial by-

products are in contact with geotextiles in pavement drainage systems. The nature of thesegeomaterials is different than regular soils, often consisting of significant amounts of fines. The

existing geotextile selection criteria may not be directly applicable to these materials and, inmost cases, their filtration or drainage performance with geotextiles should be investigated by

conducting laboratory tests.

Fly ash is one of these industrial by-products, and has increasingly being used in

transportation applications as fill materials or grout mixes for highway embankments, as well as

grout mixes for road bases .Beneficial reuse of fly ash in pavement bases has gained wideacceptance due to its abundance. For instance, 3.5 million tons of fly ash was used in pavement

construction in the U.S in 1996.

In spite of ongoing efforts to use fly ash in highway construction, limited information isavailable about its hydraulic compatibility with geotextiles. Clogging of a geotextile drain by fly

ash particles may cause significant reduction in permeability, thus reducing the flow capacity of


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the drain. Even though, the fly ash is mixed with other aggregates (e.g sand), reduction of thepermeability will be caused as a result of movement of fly ash particles through the drain.

Therefore, the fly ash should be hydraulically compatible with the adjacent geotextile. In

order to respo0nd to this need, a series of laboratory gradient ratio tests were conducted toinvestigate the clogging behavior of various geotextiles with fly ash. The retention performance

of these geotextiles was also investigated by analyzing the results obtained from the gradientratio tests.

2 Properties of Geotextiles

2.1 Physical Properties

a) Mass/ Unit Area

The mass per unit area is determined by cutting from a roll a minimum of 10 specimens,

each at least 100 mm square, and then weighing the specimens on an accurate balance. Thissimple test is frequently used for quality control and can help identify the material. It is an

important property to measure as fabric cost is directly related to mass/ unit area.

b) Nominal Thickness/ Dimensions

The nominal thickness is determined by placing a sample of the geotextile on a planereference plate and applying a pressure of 2 kN/m

2through a circular pressure plate with a cross-

sectional area of 2500mm2. A vernier gauge measures the distance between the reference plate

and pressure plate. The test is useful for quality control and classification of geotextiles.

c) Apparent Pore Size Distribution by Dry Sieving

The pore size distribution of the fabric is determined by sieving dry spherical solid glass

beads for a specified time at a specified frequency of vibration and then measuring the amountretained by the fabric sample. The test is carried out on a range of sizes of glass beads. The

apparent pore size distribution is presented on a graph using scales compatible with soil gradingcurves. In addition, the apparent opening size (090) is determined, this being the pore size at

which 90% of the glass beads are retained on and within the fabric. This test providesinformation on the pore size distribution which is an important parameter to be used in assessing

a geotextiles soil filtration capability

d) Percent Open Area Determination for Woven Geotextiles

A small section of the fabric is held within a standard slide cover, inserted into a projector and the magnified image traced on to a sheet of paper. Using a planimeter, the

magnified open spaces can be measured and expressed as a percentage of whole area. The test is primarily applicable to monofilament woven fabrics. The test provides information on pore size

openings which is important in assessing a geotextiles soil filtration capability.


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2.2 Mechanical Properties

a) Tensile Properties Using a Wide Width Strip

A specimen of the geotextile, at least 200 mm wide, is clamped within the compressive

jaws of a tensile testing machine which is capable of applying the load at a constant rate of strain.During loading, a load strain curve is plotted and, from this, the maximum load, breaking load

and the secant modulus at any specified strain may be determined.

The tensile strength of geotextiles and related materials is a very important property asvirtually all applications rely on it either as the primary or secondary function. This test is useful

for quality control and can also be used for design purposes.

b) Puncture Strength of Geotextiles

A specimen of the fabric is clamped, without tension, over an empty cylinder, and a solidsteel rod is pushed through the fabric. A load indicator attached to the rod measures the force

required to cause rupture. A CBR(soil) testing apparatus may be modified for this purpose. Thisis a common test used for quality control. The results of this test can also be used to assess the

fabrics resistance to aggregate penetration, particularly in separation applications.

c) Soil Fabric Friction Tests

The test is useful for quality control and may be used to compare different geotextiles. Itis not a suitable test for assessing the parameters to be used for the analysis for reinforced soil.

For reinforced soil applications the proposed fill material should be used in the test.

2.3 Hydraulic Properties

a) Water Permeability of Geotextiles Permittivity Method

This test measures the quantity of water which can pass through a geotextile (normal tothe plane) in an isolated condition. The permeability may be measured either in a constant head

or falling head test, although constant head testing is more common due to the high flow ratesthrough geotextiles. Since there are geotextiles of various thicknesses available it is better to

evaluate them in terms of permittivity, which relates the quantity of water passing through a

geotextile under a given head over a particular cross sectional area.

This test is useful in classifying geotextiles and for comparing the in-isolation water

permeability of geotextiles. However, in drainage and filtration applications, the influence of in-soil confinement should be establishment prior to selection a geotextile.


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b) Constant Head Hydraulic Transmissivity

This method may be used to estimate the in-plane permeability of a geotextile or acomposite drain. The sample is confined, at varying normal stresses, and the flow under a

constant head is measured.

This test is useful for classifying geotextiles and geocomposite drains and will provideinformation to allow comparisons of in-plane permeability to be made. However, in drainage

application, the influence of in-soil confinement should be established.

c) International Testing Standards for Geotextiles

British Standards (BS), European Norm (EN), International Standards Organisation (ISO)and American Society of Testing Materials (ASTM) all provide testing methods for geotextiles

and related products. Some of these test methods with respect to the tests discussed in the previous section are given for reference as follows. (cross references for different standards are

given in the bracket).

3 Fly Ash

Around 110 million tones of fly ash get accumulated every year at the thermal powerstations in India. Internationally fly ash is considered as a byproduct which can be used for many

applications. Fly Ash Missions was initiated in 1994 to promote gainful and environmentfriendly utilization of the material. One of the areas identified for its bulk utilization was in

construction of roads and embankments. Central Road Research Institute (CRRI), New Delhi,chosen as the Nodal Agency for this activity, has undertaken many demonstration projects.

Some of these are jointly with Fly Ash Mission (Presently Fly Ash Utilisation Programme). As aresult of experience gained through these projects, specifications for construction of road

embankments and guidelines for use of fly ash for rural roads were compiled and have since been published by the Indian Roads Congress. Fly ash utilization in the country rose from 3 per

cent (of 40 million tonnes) of fly ash produced annually in 1990s to about 32 per cent (of 110million tones) of fly ash generated annually now. Out of this total utilization, about 22 per cent,

amounting to 7.75 million tones, was used in the area of roads and embankments last year.

3.1 Advantages of Flyash

3.1.1 Advantages of using fly ash for road construction

Fly ash is a lightweight material, as compared to commonly used fill material(local soils), therefore, causes lesser settlements. It is especially attractive for

embankment construction over weak subgrade such as alluvial clay or silt whereexcessive weight could cause failure.

Fly ash embankments can be compacted over a wide range of moisture content,and therefore, results in less variation in density with changes in moisture content.Easy to handle and compact because the material is light and there are no large


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lumps to be broken down. Can be compacted using either vibratory or staticrollers.

High permeability ensures free and efficient drainage. After rainfall, water gets

drained out freely ensuring better workability than soil. Work on fly ash fills/embankments can be restarted within a few hours after rainfall, while in case of

soil it requires much longer period.

Considerable low compressibility results in negligible subsequent settlementwithin the fill.

Conserves good earth, which is precious topsoil, thereby protecting theenvironment.

Higher value of California Bearing Ratio as compared to soil provides for a more

efficient design of road pavement.

Pozzolanic hardening property imparts additional strength to the road pavements/embankments and decreases the post construction horizontal pressure on

retaining walls.

Amenable to stabilization with lime and cement.

Can replace a part of cement and sand in concrete pavements thus making themmore economical than roads constructed using conventional materials.

Fly ash admixed concrete can be prepared with zero slump making it amenablefor use as roller compacted concrete.

Considering all these advantages, it is extremely essential to promote use of flyash for construction of roads and embankments.

3.1.2 Economy in use of fly ash

Use of fly ash in road works results in reduction in construction cost by about 10 to 20per cent. Typically cost of borrow soil varies from about Rs. 100 to 200 per cubic meter. Fly ashis available free of cost at the power plant and hence only transportation cost, laying and rolling

cost are there in case of fly ash. Hence, when fly ash is used as a fill material, the economyachieved is directly related to transportation cost of fly ash. If the lead distance is less,

considerable savings in construction cost can be achieved. Similarly, the use of fly ash in pavement construction results in significant savings due to savings in cost of road aggregates. If

environmental degradation costs due to use of precious top soil and aggregates from borrowareas quarry sources and loss of fertile agricultural land due to ash deposition etc. the actual

savings achieved will be much higher and fly ash use will be justified even for lead distances upto say 100 km.

3.1.3 Environmental Impact of Fly ash Use

Utilization of fly ash will not only minimize the disposal problem but will also help in

utilizing precious land in a better way. Construction of road embankments using fly ash, involvesencapsulation of fly ash in earthen core or with RCC facing panels. Since there is no seepage of

rain water into the fly ash core, leaching of heavy metals is also prevented. When fly ash is usedin concrete, it chemically reacts with cement and reduces any leaching effect. Even when it is


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used in stabilization work, a similar chemical reaction takes place which binds fly ash particles.Hence chances of pollution due to use of fly ash in road works are negligible.

3.1.4 Characterisation of Fly Ash

Engineering and chemical properties of Indian ashes of various power plants tested at

CRRI have been found to be favourable to construction or roads and embankments. Properties offly ash from different power plants vary and therefore it is recommended that characterization of

ash proposed to be used should be conducted to establish the design parameters. The propertiesof ash depend primarily on type of coal and its pulverization, burning rate and temperature,

method of collection, etc. The significant properties of fly ash that must be considered when it isused for construction of road embankments are gradation, compaction characteristics, shear

strength, compressibility and permeability properties.

Individual fly ash particles are spherical in shape, generally solid, though some timeshollow. Fly ash possesses a silty texture and its specific gravity would be in the range of 2.2 to

2.4, which is less than natural soils. Fly ash is a non-plastic material. Typical propertie3s ofIndian fly ash compared to different types of soil are given in the following table:

Table 1.1 : Characterization of fly ash compared to other soil

Parameter Gravel Sand Silt Clay Fly ash

Specific gravity 2.65-2.67 2.65-2.67 2.67-2.70 2.70-2.80 1.90-2.55

Plasticity Index NP NP 1%-17% >17% NP

Maximum Dry Density

(g/cc)

1.76-2.27 1.76-1.84 1.52-2.08 1.44-1.84 0.9-1.60

Optimum Moisture

Content (%)

7-18 9-15 10-20 15-30 18-38

Cohesion (kN/m2) 0 0 6 >6 Negligible

Angle of InternalFriction (f)

35o -50 o 27.5o - 45o 27o - 35o 0o - 6o 30o - 40o

Coefficient ofConsolidation Cv

(cm2/sec)

- - 5 x 10-3 0.001 2x10

-41.75x10-5

2.01x10-

3

Compression Index - 0.01 0.05 0.05 0.15 0.21 2.6 0.05 0.4

Permeability (cm/sec) 1 10-1 10-3 10-5 10-7 10-7 & less 8x10-6

7x10-4

Coefficient of

Uniformity

>4 >6 - - 3.1 10.7


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3.1 Objectives

To determine the hydraulic characteristic features of reinforced soil behaving with fly ash

and geotextile. So far the soil stress has been analyzed in order to perform hydraulic property wehad ensure had two tests,

a. Long term flow test

b. Gradient ratio test

3.2 Materials Used

1) Sand2) Fly ash

3) Geotextiles

3.3 Methods

3.3.1 Long term flow test

Filtration was developed by Ecole Polytechnique of Montreal (EPM) in which flow rateof soil geotextile system is measured at a constant head. The US corps of Engineers established a

direct measure of geotextile clogging potential with a gradient ratio apparatus.

This long term filtration determines the long term flow as described by EPM. Soil can becompacted to a specified density in this apparatus with a proctor hammer to represent the field

density.

Takes long time to establish transition time to stable or clogged flow

Potential for bacterial clogging

Deaired/ deionized water needed

3.3.2 Gradient Ratio Test

Geotextiles are increasingly being used as a filter layer in place of graded filter in a

variety of civil engineering situations. They retain erodible soil particles and provide sufficienthydraulic conductivity to permit the free low of water. It is estimated that the hydraulic

properties of geotextiles along differ markedly from that of soil-geotextile system, the hydraulic behavior of combined soil geotextile influence the filtration ability of the geotextile in the long

term flow situation, the flow rate of the soil geotextile system decreases as the pores ofgeotextiles get clogged. It is therefore, imperative that the clogging resistance of geotextiles be

evaluated to ensure adequate long term filtration performance. Two type of resisting viz.filtration test and gradient ratio test are presently being used.


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The US corps of engineers established a direct measure of geotextiles clogging potentialwith a gradient ratio apparatus.

The gradient ratio is defined as the hydraulic gradient through the geotextiles plus 25 mm

of the soil divided by the hydraulic gradient through the adjacent 50 mm of the soil.

The gradient ratio test specified by the US corps of engineers. Soil can be compacted to aspecified density in this apparatus with a protector hammer to represent the field density.

3.3.3 Mix Proportion of SamplesTABLE 2.1: Sand Vs Fly Ash proportion

SAND IN % FLY ASH IN %

100 0

80 20

60 40

40 60

20 80

0 100

3.3.4 Apparatus Setup

Soil Geotextile permeameter equipped with support stand, soil-geotextilesupport screen, piping barriers (caulk), claming brackets, and plastic tubing.

Use of 100mm and 150mm dia permeameter is described

Two constant water head devices, one mounted on a jack stand (adjustable) andone stationary

Need of soil leveling device

Manometer Board, of parallel glass tubes and measuring rulers

Two soil support screens. Of approximately 5mm mesh ahs been used

Soil support cloth, of 150m (No.100) mesh, or equivalent geotextile

Use of thermometer (0 to 5010C)

Graduated Cylinder, 1001cm3

capacity

Stop Watch


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Balance, or scale of at least 2-kg capacity and accurate to =1g

Carbon Dioxide, (CO2), gas supply and regulator

Geotextile

Water Recirculation System

Water Dearing System, with a capacity of approximately 1700 L/day (500gal/day)

Algae Inhibitor, or micro screen

150m Mesh Screen, (No.100), or equivalent geotextile for manometer ports

Soil Sample Splitter (optional)

Pan, for drying soil

4 Test Procedure

4.1 Long Term Flow Test

1. Cut a geotextile specimen of 116mm diameter

2. Saturate geotextile specimen by soaking in distilled water for 24 hours3. Place cylindrical metallic mould on metallic base and attach it with metallic collar

4. Compact soil in three layers with proctor hammer to give specified density (soilcompaction behaviour is predetermined)

5. Remove the collar and level off the surface6. Weigh the cylindrical mould and compacted soil

7. Determine soil moisture content8. Place the saturated geotextile specimen on the cylindrical metallic base which is

filled with water. Close the outlet tube

9. Place O-rings10. Place the cylindrical metallic mould with compacted soil over geotextile specimen

and the cylindrical metallic base carefully and clamp with nuts and bolts.

Geotextile specimen should be stretched or slacked11. Place the cylindrical PVC pipe over the cylindrical metallic mould

12. Pour water slowly op top of the soil specimen till a constant head is attained.Connected the inlet of the cylindrical PVC pipe to water reservoir

13. Saturate the soil specimen till all the pezionmetric heads show constancy14. To start filtration test, open outlet, measure the flow rate with measuring cylinder

15. Measure flow rate at 15 min, 30 min, 60 min, 2 hrs, 4 hrs, 8 hrs etc..,

4.2 Gradient Ratio Test

1. Cut a geotextile specimen of 116mm diameter2. Saturate geotextile specimen by soaking in distilled water for 24 hours

3. Place cylindrical metallic mould on metallic base and attach it with metallic collar4. Compact soil in three layers with proctor hammer to give specified density (soil

compaction behaviour is predetermined)5. Remove the collar and level off the surface


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6. Weigh the cylindrical mould and compacted soil7. Determine soil moisture content

8. Place the saturated geotextile specimen on the cylindrical metallic base which isfilled with water. Close the outlet tube

9. Place O-rings10. Place the cylindrical metallic mould with compacted soil over geotextile specimen

and the cylindrical metallic base carefully and clamp with nuts and bolts.Geotextile specimen should be stretched or slacked.

11. Place the cylindrical PVC pipe over the cylindrical metallic mould12. Pour water slowly on top of the soil specimen till a constant head is attained.

Connected the inlet of the cylindrical PVC pipe to water reservoir.13. Saturate the soil specimen till all the peziometric heads show constancy

14. To start filtration test, open outlet. Measure the flow rate with measuring cylinder15. Read peizometric levels H1, H2 and H3 till a stabilized flow rate attained.

5 Results and Discussion

5.1 Long Term Flow Test

SPECIFICATION :SPECIMEN : GeotextileSAND : 20%

FLY ASH : 80%SPCIMEN DIA : 116mm

MOULD OFCOMPACTION SOIL: 101.6mm dia X 114.3mm dia

HEAD OF WATER : 375mm

Table 2.1 Table showing flow rate through soil mixed with flyash in varying proportion

Sand 20%Fly ash 80%

Sand 60%Fly ash 40%

Sand 80%Fly ash 20%

Sand 100%Fly ash 0%

Sand 0%Fly ash 100%

Time

inhrs

(t)

Collecting

Waterin ml

(V)

FlowRate

inml/m

in(Q)

Collecting

Waterin mi

(V)

FlowRate

inml/m

in(Q)

Collecting

Waterin mi

(V)

FlowRate

inml/m

in(Q)

Collecting

Waterin mi

(V)

FlowRate

inml/m

in(Q)

Collecting

Waterin mi

(V)

FlowRate

inml/m

in(Q)

.25 50 3.33 60 4 100 6.67 8850 570 40 2.67

.5 80 2.66 100 3.33 200 6.67 17250 575 70 2.33

1 150 2.50 170 2.83 380 6.33 33750 562.5 120 2

2 250 2.08 320 2.67 740 6.16 60100 500.8

3

230 1.91

3 340 1.88 420 2.33 1060 5.89 84950 471.94

320 1.78

4 430 1.79 550 2.92 1280 5.33 105600 440 420 1.75

5 510 1.70 650 2.16 1450 4.83 125850 419.5 500 1.67

6 580 1.61 750 2.08 1610 4.47 143500 398.6 580 1.61


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1

5.2 Gradient Ratio Test

SPECIFICATION:SPECIMEN : GeotextileSAND : 20%

FLYASH : 80%SPECIMEN DIA : 116mm

MOULD OFCOMPACTION SOIL: 101.6mm dia X 114.3mm dia

HEAD OF WATER : 375mm

Table 2.2Table showing gradient ratio through soil mixed with flyash in varying

proportion

Sand 20%

Fly ash 80%

Sand 40%

Fly ash 60%

Sand 60%

Fly ash 40%

Sand 80%

Fly ash 20%

Sand 100%

Fly ash 0%

Sand 0%

Fly ash 100%

PIEZOMETRIC LEVELSIN cm






Ti

meinhr

s(t)

H

1

H

2

H

3

GRADIENT

RATIOGR=(H2-

H1)/[(H3-H2)/2]

H

1

H

2

H

3

GRADIENT

RATIOGR=(H2-

H1)/[(H3-H2)/2]

H

1

H

2

H

3

GRADIENT

RATIOGR=(H2-

H1)/[(H3-H2)/2]

H1

H

1

H

2

H

3

GRADIENT

RATIOGR=(H2-

H1)/[(H3-H2)/2]

H

1

H

2

H

3

GRADIENT

RATIOGR=(H2-

H1)/[(H3-H2)/2]

H

1

H

2

H

3

GRADIENT

RATIOGR=(H2-

H1)/[(H3-H2)/2]

0.2

5

9.7

36

46

.8

4.87 25

.5

36

.8

46

.3

2.37 12

39

.8

42

.5

20.59

14

18

29

0.72 27

.3

36

.4

13

.4

-0.79

9 24

49

.7

1.16

0.5

10

36

.2

47

4.85 26

37

46

.5

2.31 12

40

.2

44

.5

13.11

17

.6

22

34

0.73 28

38

14

.5

-0.85

11

.3

26

.8

50

.4

1.31

1 11.

3

36

.5

47

.2

4.71 26

.1

37

.3

46

.5

2.43 13

.2

39

.2

46

7.64 22

.2

31

.4

44

.6

1.39 27

.7

37

.4

17

-0.95

14

31

.4

50

.7

1.80

2 12.

4

36

.9

47

.5

4.62 26

.2

37

.3

46

.2

2.49 14

.8

39

.5

46

.8

6.76 25

.5

35

47

1.58 27

.6

38

.7

20

.3

-1.20

17

34

.6

50

.9

2.15

3 1

4.

5

3

7

4

7

.9

4.12 2

6

.2

3

7

.3

4

6

.1

2.52 1

8

.2

4

0

4

6

.8

6.41 2

5

.8

3

5

.3

4

7

1.62 2

7

.6

3

8

.7

2

2

.8

-

1.39

1

9

3

7

5

1

2.57

4 1

7

3

7.3

4

7.4

4.02 2

5.3

3

7

4

5.2

2.85 2

1.2

4

0.2

4

7.1

5.50 2

5.5

3

6

4

4.6

2.44 2

7.6

3

8.7

2

4.5

-

1.56

2

0.6

3

8.3

5

1

2.78

5 1

9.4

3

7.8

4

7

4.00 2

5.1

3

7

4

5

2.97 2

2.2

4

0.4

4

7.4

5.20 2

6

3

7.4

4

6.6

2.47 2

6.8

3

7.4

2

6.7

-

1.98

2

2

3

7.4

5

1

2.26

6 21.

37

46

3.57 24

36

45

2.92 22

40

47

5.15 26

36

47

1.96 25

36

28

-2.88

22

37

51

2.02


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5 .6

.6

.8

.8

.4

.7

.8

.8

.8

.3

.7

.8

.8

The studies were conducted with soils available in the stretch of Palani to Dindigul which

contains mostly black cotton soil, red soil, a small amount of murum in certain areas. The soilsample is prepared as well graded with sieves, the thickness of the soil sample used for the studyis as per ASTM standards.

6 Conclusion

1. The flow rate for pure sand is very high and is equal to 570ml/min. When flyashis mixed, even for 20% fly ash, which is the least proportion tried in the project,

the maximum flow rate at the beginning is only 6ml/min. This is a huge reductionin the flow rate. Hence addition of fly ash with sand reduces the flow rate largely

and brings the flow rate to 1/100th

of the flow are for pure sand.2. Percentage reduction in the flow rate for pure sand after 6 hours is about 30%. But

for fly ash mixes, the maximum reduction % is 52 and that is for 80% fly ash. Forentire replacement of sand with fly ash, the % reduction in flow rate is only 40%.

Hence the grain size distributions of fly ash and sand are such a way that there ismaximum reduction in flow rate at 80% replacement.

3. Flow rate is decreasing continuously with time for all mixes. At the initial stages,(i.e) upto t = 1 hour, the reduction in flow rate is fast. After t = 1 hr, the reduction

is less and the slope of the curve becomes gentle. Then the curve becomes almostflat showing steady unclogged flow.

4. As the % of replacement increases, the flow rate also decreases. When comparedto the flow rate for pure sand, the effect of % of flyash on flow rate seems to

insignificant. Even then relatively, the flow rate reduces as the flyash content

increases.5. The preferable ratio of flyash is 20% from Gradient ratio point of view. Gradient

ratio for this mix is the least among all the mixes.

6. There is no significant change in the gradient ratio with time for various mixes.7. Generally as an average, the gradient ratio increases with time. This means

resistance to flow increases with time.8. As the % of flyash increases beyond 20%, the flow rate decreases more

9. At all the time intervals, for 40% flyash mix, the values of gradient ratio are highindicating more resistance to flow. Further analysis on the grain size distributions

of flyash and sand is to be made to understand this behavior. For other mixesexcept 40% flyash mix, the difference in gradient ratio is less.

7. References

1. R M Koerner. Designing with Geosynthetics. 4th edition, Prentice-Hall Inc, 1999.2. Swami Saran. Reinforced soil and its applications IBH publications, 2004.

3. Mitchell, J.K. (1976). Fundamentals of Soil Behaviour, John Wiley and Sons, NewYork.

4. IS: 2720 (Part 4) 1985, Methods of Test for Soils Part - 4 Grain Size Analysis, BIS,New Delhi, India.


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5. L.Manjesh, (2006) Studies on the Performance of Fly-Ash Stabilized Soils underFatigue Loading. A thesis submitted to Bangalore University for Degree of Doctor

of Philosophy in Civil engineering.6. Palit, K. Sudhakar Reddy and Pandey, B.B., Development of a Test Set-Up for

the Evaluation of Pavement materials under Repeated Load Conditions Technical PapersPublished in 62nd Session at Kochi.

7. Pavate T.V and Vishwesswaraiya T.G (1972), Stabilization of Lateritic soils,Proceedings of the symposium on strength and deformation behavior of soils,

vol.1. Bangalore, India.8. A.A.AlRawas, A.W.Hago, H.ASarmi(2005), Effect of lime, cement and Sarooj

(artificial pozzolana) on the swelling potential of an expansive soil from Oman.Building and Environment,vol 40, pp. 68 1687.

9. G.Rajasekaran, S.Narasimha Rao, (1996), Lime stabilization technique for theimprovement of marine clay, Soils and Foundations vol 37, pp 94104.

10. S.Narasimha Rao, G.Rajasekaran, (1996), Reaction products formed in lime-stabilizedmarine clays, Journal of Geotechnial Engineering, ASCE 122, pp 329336.

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