ABSTRACT

Soil is the basic foundation for any civil engineering structures.It is required to

bear the loads without failure.In some places, soil may be weak which cannot resist

the oncoming loads.In such cases,soil stabilization is needeed.Numerous methods

are available in the literature for soil stabilization.But sometimes,some of the

methods like chemical stabilization,lime stabilization etc. adversly affects the

chemical composition of the soil.

In this study,fly ash and lime were mixed with clay soil to investigate the relative

strength gain in terms of unconfined compression,bearing capacity and

compaction.The effect of fly ash and lime on the geotechnical characteristics of

clay-fly ash and clay-lime mixtures was investigated by conductiung standard

Proctor compaction tests,unconfined compression tests,CBR tests and permeability

test.The tests were performed as per Indian Standard specifications.

The following materials were used for preparing the samples:

Clayey soil

Fly ash

Lime

The soft clay used for these experiments was brought from a site,near

Kumarakom.The physical properties of the soil were determined as per IS

specifications.

Fly ash for the study was brought from Hindustan Newsprints,Piravam.it is finely

divided residue resulting from the combustion of ground or powdered coal from

electric generating plants. It has high water absorption capacity.

Lime for the study is locally available.it imparts much strength to the soil by

pozzolanic reaction which is explained later in the report.

In this test programme,without additives clay was tested to find the optimum

moisture content ,CBR value ,plasticity index and unconfined compression

strength.Fly ash and lime were added in varying percentages and that fraction for

which maximum strength is obtained was found out.The mixture is cured for 3,7

and 14 days.

CHAPTER 1

INTRODUCTION

General

Transport in the Republic of India is an important part of the nation's economy.

Roads are the vital lifelines of the economy making possible trade and commerce.  

They are the most preferred modes of transportation and considered as one of the

cost effective modes. An efficient and well-established network of roads is desired

for promoting trade and commerce in any country and also fulfills the needs of a

sound transportation system for sustained economic development. To provide

mobility and accessibility, all weather roads should connect every nook and corner

of the country. To sustain both static and dynamic load, the pavement should be

designed and constructed with utmost care. The performance of the pavement

depends on the quality of materials used in road construction.

Sub grade is the in situ material upon which the pavement structure is placed.

Although there is a tendency to look at pavement performance in terms of

pavement structures and mix design alone, the subgrade soils can often be the

overriding factor in pavement performance. The construction cost of the pavements

will be considerably decreased if locally available low cost materials are used for

construction of lower layer of pavements such as subgrade, sub base etc.If the

stability of local soils is not adequate for supporting the loads, suitable methods to

enhance the properties of soil need to be adopted. Soil stabilization is one such

method. Stabilizing the subgrade with an appropriate chemical stabilizer (such as

Quicklime, Portland cement, Fly Ash orComposites) increases subgrade stiffness

and reduces expansion tendencies, it performs as a foundation (able to support and

distribute loads under saturated conditions). This report contains a summary of the

performance of lime and fly ash used with clay.

Fly ashes are finely divided residue resulting from the combustion of ground or

powdered coal from electric generating plants.

Lime is another additive used, which is locally available, to improve subgrade

characteristics. It is obtained by heating limestone at elevated temperatures.

SCOPE OF THE PROJECT

The soil used in the study is natural clay brought from Kumarakom.Pavement

subgrade over there is composed of clayey soil whose bearing capacity is

extremely low.Due to this reason ,the roads require periodic maintenance to take

up repeated application of wheel loads.This proves to be costly ,and at the same

time, conditions of raods during monsoon seasons is extremely poor.Therefore, a

thought on how to enhance the stability of roads by chaper means demands

appraisal.

Soil stabilization can be done using different additives ,but use of fly ash which is

a waste material from thermal power plants,at the same time difficult-to-dispose

material will be much significant.

OBJECTIVES OF THE PROJECT

The major objectives of the project are:

1. To explore the possibility of using flyash in road construction programme.

2. To study the effect of lime and flyash on proctor’s density and OMC of

clayey soil.

3. To study the effect of lime and flyash on the consistency limits of clayey

soil.

4. To study the changes in CBR of soil by the addition of lime and fly ash

5. To study the effect of curing period on the properties of clayey soil.

CHAPTER 2

LITERATURE REVIEW

General

Stabilization is the process ofblending and mixing materials with a soil to

improve certain properties of the soil. The process may include the blending of

soils to achieve adesired gradation or the mixing of commerciallyavailable

additives that may alter the gradation, texture or plasticity, or act as a binder for

cementationof the soil.

The process of reducing plasticity and improving the texture of a soil is called soil

modification. Monovalent cations such as sodium and potassium are commonly

found in expansive clay soil and these cations can be exchanged with cations of

higher valenciessuch as calcium which are found in lime and flyash. This ion

exchange process takes place almost rapidly, within a few hours. The calcium

cations replace the sodium cations around the clay particles, decreasing the size of

bound water layer, and enable the clay particle to flocculate. The flocculation

creates a reduction in plasticity, an increase in shear strength of clayey soil and

improvement in texture from a cohesive material to a more granular, sand-like soil.

The change in the structure causes a decrease in the moisture sensitivity and

increase the workability and constructability of soil. Soil stabilization includes the

effects from modification with a significant additional strength.

Soil structure

The clay particles in the soil structure are arranged in sheet like structures

composed of silica tetrahedral and alumina octahedra. The sheets form many

different combinations, but there are three main types of formations .the first is

kaolinite,which consists of alternating silica and alumina sheets bonded together.

This form of clay structure is very stable and does not swell appreciably when

wetted .the next form is montmorillonite, which is composed of two layers of silica

and one alumina sheet creating aweak bond between the layers. This weak bonding

between the layers allows water and other cations to enter between the

layers,resulting in swelling in the clay particle. The last type is illite, which is very

similar to montmorillonite ,but has potassium ions between each layer which help

bond the layers together. Inter layer bonding illite is therefore stronger than for

montmorillonite,but weaker than kaolinite.

Clay particles are small in size but have alarge to mass ratio,resulting in alarger

surface area available for interaction with water and cations.the clay particles have

negatively charged surfaces that attract cations and polar molecules,including

water forming a boundwater layer around the negatively charged clay particles.

The amount of water surrounding the clay particles is related to the amount of

water that is available for the clay particle to take in and release. This moisture

change around the clay particles causes expansion and swelling pressures within

clays that are confined .

Uses of stabilization

Pavement design isbased on the premise that minimum specifiedstructural quality

will be achieved for each layerof material in the pavement system. Each layermust

resist shearing, avoid excessive deflectionsthat cause fatigue cracking within the

layer or inoverlying layers, and prevent excessive permanentdeformation through

densification. As the qualityof a soil layer is increased, the ability of that layerto

distribute the load over a greater area isgenerally increased so that a reduction in

therequired thickness of the soil and surface layersmay be permitted.

Quality improvement.

The most common improvementsachieved through stabilization includebetter soil

gradation, reduction of plasticity indexor swelling potential, and increases in

durabilityand strength. In wet weather, stabilizationmay also be used to provide a

working platformfor construction operations. These types of soilquality

improvement are referred to as soil modification.

Thickness reduction.

The strength and stiffnessof a soil layer can be improved through theuse of

additives to permit a reduction in designthickness of the stabilized material

compared withan unstabilized or unbound material.

STABILIZATION TECHNIQUES

Stabitization with portland cement

Portland cement can be used either to modify or improve the quality of the soil into

a cemented mass with increased strength and durability. The amount of cement

used will depend upon whether the soil is to be modified or stabilized.

Cement stabilization is most commonly used for stabilizing silt, sandy soils with

small quantities of silt or clayey fractions stabilization of soil with cement has been

extensively used in road construction. Mixing the pulverized soil and compact the

mix to attain a strong material does this stabilization. The material thus obtained by

mixing soil and cement is known as ‘soil cement’. The soil content becomes a hard

and durable structural material as the cement hydrates and develops strength. The

cementing action is believed to be the result of chemical reaction of cement with

the siliceous soil during hydration.

Stabilization with bitumen

Stabilization of soils and aggregates with asphalt differs greatly from cementand

lime stabilization. The basic mechanism involved in asphalt stabilization of fine

grained soils is a water proofing phenomenon. Soil particles soil agglomerates are

coated with asphalt that prevents or slows the penetration of water, which could

normally result in a decrease in soil strength. In addition, asphalt stabilization can

improve durability characteristics by making the soil resistant to the detrimental

effects of water such as volume. In non-cohesive material such as sand and gravel,

crushed gravel, and crushed stone, two basic mechanisms are active: water

proofing and adhesion. The asphalt coating on the cohesion less materials provides

a membrane, which prevents or hinders the penetration of water and thereby

reduces the tendency of the material to lose strength in the presence of water. The

second mechanism has been identified as adhesion. The aggregate particle adheres

to the asphalt and the asphalt acts as a binder or cement. The cementing effect thus

increases the shear strength by increasing adhesion. Criteria for design of

bituminous stabilized soils and aggregates are based almost entirely on stability

and gradation requirements. Freeze-thaw and wet durability test are not applicable

for asphalt-stabilized mixtures.

Stbilization with lime-cement and lime-bitumen

The advantages in using combination stabilizers are that one of the stabilizers in

the combination compensates for the lack of effectiveness of the other in treating a

particular aspect or characteristics of a given soil. For instance in clay areas devoid

of base material, lime have been used jointly with other stabilizers notably Portland

cement or asphalt, to provide acceptable base courses. Since Portland cement or

asphalt cannot be mixed successively with plastic clays, the lime is incorporated

into the soil to make it friable, thereby permitting the cement or asphalt to be

adequately mixed. While such stabilization might be more costly than the

conventional single stabilizer methods, it may still prove to be economical in areas

where base aggregate costs are high. Two combination stabilizers are considered in

this section.

1. lime-cement

2. lime-asphalt

Lime-cement

Lime can be used as an initial additive with Portland cement or the primary

stabilizer. The main purpose of lime is to improve workability characteristics

mainly by reducing the plasticity of soil. The design approach is to add enough

lime to improve workability and to reduce the plasticity index to acceptable levels.

The design lime content is the minimum that achieves desired results.

Lime-asphalt

Lime can be used as an initial additive with asphalt as the primary stabilizer. The

main purpose of lime is to improve workability characteristics and to act as an anti-

stripping agent. In the latter capacity, the lime acts to neutralize acidic chemicals in

the soil or aggregate, which tend to interfere with bonding of the asphalt.

Generally, about 1-2 percent lime is all that is needed for this objective.

Stabilazation by geo-textiles and fabrics

Introducing geo-textiles and fabrics that are made of synthetic materials, such as

polyethylene, polyester, and nylon, can stabilize the soil. The geo-textile sheets are

manufactured in different thickness ranging from 10 to 300 mils (1mil=0.254mm).

The width of sheet can be upto 10m. These are available in rolls of length upto

about 600m.

Geotextiles are permeable. Their permeability is compared to that of fine sand to

course sand and they are strong and durable.

STABILIZATION WITH LIME

Lime stabilization is done by adding lime to soil. This is useful for the stabilization

of clayey soil. When lime reacts with soil there is exchange of cations in the

adsorbed water layer and a decrease in the plasticity of the soil occurs. The

resultant material is more friable than the orginal clay, and is more suitable as

subgrade.

Lime is produced by burning of limestone in kiln. The quality of lime obtained

depends on the parent material and the production process. And there are basically

5 types of limes

1. High calcium, quick lime (CaO)

2. Hydrated high calcium lime [Ca(OH)2]

3. Dolomitic lime [CaO+MgO]

4. Normal, hydrated Dolomitic lime [Ca(OH)2+MgO]

5. Pressure, hydrated dolomitic lime[Ca(OH)2+MgO2]

The two primary types of lime used in construction today are quick lime(calcium

oxide) and hydrated lime (calcium hydroxide).Heating limestone at elevated

temperatures produce quick lime and addition of water to quick lime produces

hydrated lime.

Equation shows the reaction that occurs when limestone is heated to produce quick

lime with carbon dioxide produced as by-product.

CaCO3+heat CaO+CO2

Addition of water to quick lime produces hydrated lime along with heat as

byproduct:

CaO+H2O Ca (OH)2+Heat

For stabilization with lime,soil conditions and mineralological properties have a

significant effect on the long term strength gain.

Mechanism

For soil stabilization with lime, soil conditions and mineralogical properties have a

significant effect on the long-term strength gain. A pozzolanic reaction between

silica and alumina in the clay particles and calcium from the lime can form a

cemented structure that increases the strength of the stabilized soil. Residual

calcium must remain in the system to combine with the available silica or alumina

to keep the pH high enough to maintain the pozzolanic reaction. Soil that should be

considered for lime treatment include soils with a PI that exceeds 10 and have

more than 25 percent passing the #200 sieve.

In lime stabilization the liquid limit of soil generally decreases but the plastic limit

increases. Thus the plasticity index of the soil decreases. The strength of the lime

stabilized soil is generally improved. It is partly due to the decrease in the plastic

properties of the soil and partly due to the formation of cementing material.

Increase in the unconfined compressive strength is as high as 60 times. The

modulus of elasticity of the soil also increases substantially.

Addition of lime causes a high concentration of calcium ions in double layer. It

causes a decrease in the tendency of attraction of water. Consequently, the

resistance of soil to water absorption, capillary rise and volume changes on wetting

or drying is substantially increased. The lime-stabilized bases or sub bases form a

water resistant barrier which stops penetration of rain water. There is an increase in

optimum water content and a reduction in maximum density. In swampy areas

where the water content is above the optimum, application of lime to soilhelps in

drying of soil.

Cyclic freezing and thawing can causes a temporary loss of strength, but because

of subsequent healing action, there is no loss of strength in long run.

Construction methods used in lime stabilization are similar to those used in cement

stabilization. However , the following points are to be noted.

1. As the reaction in the case of lime is low,there is no maximum time limit

between the addition of lime to the soil and the completion of

compaction. However ,care should be taken to avoid carbonation of lime

in the process.

2. Lime may be added in the form of slurry instead of dry powder.

3. A rest period of 1 to 4 days is generally required for spreading lime over

heavy clay before final mixing is done. This facilitates proper mixing of

lime and soil.

4. The soil-lime is compacted to the required maximum dry density.

After compaction, the surface is kept moist for 7 days and then covered with a

suitable wearing coat. Sometimes, the wearing coat is applied soon after the

compaction to help hold the moisture.

STABILIZATION WITH FLYASH

Class C flyash is an industrial byproduct generated at coal fired electricity

generating power plants that contains silica,alumina and calcium based

minerals.Upon exposure to water,these calcium compounds hydrate and produce

cementitious products similar to the products formed during the hydration of

Portland cement.The rate of hydration for flyash is much more rapid than Portland

cement.It is therefore more desirable to mix and compact flyash as quickly as

practical.

The hydration property depends on coal source, boiler design and the type of ash

collection system.The coal source governs the amount and type of organic matter

present in it. Eastern coal source contain small amount of calcium. This class F

flyash does not exhibitself-cementing characteristics. Western coals contain higher

amount of calcium (about 20%-35%) and are classified as class C flyash.

The amount of calcium oxide in flyash is lower than that of lime and much of it is

combined with silicates and aluminates, so flyash has less effect on plasticity than

lime.

Boiler design and operation depends on the rate at which the hydration occurs.

During combustion the inorganic matter is fused consequently rapid cooling of

fused particles occur. So the flyash particles are non crystalline in nature.

Compaction time after mixing is critical to achieve maximum density and strength.

When compaction is delayed hydration products begin to bond with loose particles

and disruption of these aggregation is required to densify the material. So a portion

of compactive energy isutilized in overcoming cementation and maximum

densities are reduced.

In fly ash the high loss on ignition is due to the presence of unburnt carbon. The

combined amount of silica alumina and iron oxide (84.6%) indicate its suitability

as a pozzolanicmaterial.fly ash is no-plastic in nature.its moisture condition does

not predominantly affect the dry density. The fly ash has high angle of internal

friction.

The grain size distribution of is shown if fig 2. Fly ash is a fine grained

material .about 86% of the sample passes through 75 micron sieve indicating that

fly ash is essentially a silt size material.

CHAPTER 3

EXPERIMENTAL PROGRAMME

INTRODUCTION

In this chapter, a brief review of various experiments conducted using clay and the

same stabilized with lime and flyash are explained.

MATERIALS USED

1. Clayey soil

Soil is brought from a paddy field in kumarakom.Soil over thereis highly

plastic clay. Therefore the strength of pavement subgrade needs to be

ascertained to withstand the compressive loadunder traffic.

Properties of clay usedin the study:

Sl No: Properties Values

1 CBR value 4.3%

2 Max.dry density 1517 kg/m3

3 Optimum moisture

content

20%

4 Liquid limit 36%

5 Plastic limit 26%

6 Plasticity index 10

0.001 0.01 0.10

20

40

60

80

100

120

Particle size distribution for clayey soil

per

cen

tage

pas

sin

g (%

)

2.Additives

Theadditives used for stabilization and modification include lime and flyash.

The soils weremixed with each of these additives for which there were

reasonable expectations of improved engineering properties. The amount of

additive used was determined based on testing the strength for addition of

varying percentages and selecting the one with greatest strength. The lime

percentage was fixed at 10% and flyash 14%.

Physical properties and chemical composition of flyash

Physical properties

Specific gravity 2.27

Loss on ignition 11.8%

Chemical composition

Silica (SiO2) 58.3%

Alumina (Al2O3)+Iron oxide (Fe2O3) 26.3%

Calcium oxide (CaO) 2.2%

Magnesium oxide (MgO) 0.3%

LAB TESTING

The various tests conducted on the sample are the following:

1.Atterberg limits

2. Specific gravity

3. Direct shear test

4. Proctor compaction test

5. CBR test

6. Unconfined compression test(UCS)

Firstly the above tests were conducted on plane clay sample to determine its

properties.UCS test is conducted to evaluate it strength. Thereafter, certain

percentages of lime and flyash are added to the clay sample to stabilize it. And the

percentages of the above additives which produce the optimum strength to the soil

are chosen by conducting UCS test on them.

Soil preparation

The soil was collected from site in large sacks. It is brought to the lab and is dried

in oven for 24 hours in large pans. This soil due to loss of water formed big lumps

which is broken to smaller pieces or even fine powder and is sieved according to

the needs of different experiments.

Compaction test

Compaction is the densification of soil by reduction of air voids. The purpose of a

laboratory compaction test is to determine, the quantity of water to be added for

field compaction of soil and resultant density expected. When water is added to

dry fine grained soil, the soil absorbs water. Addition of more water helps in

sliding of particles over each other. This assists the process of compaction. Up to a

certain point, additional water helps in reduction of air voids,but after a relatively

high degree of saturation is reached, the water occupies the space ,which could be

filled with soil particles, and the amount of entrapped air remains essentially

constant.Therfore,there is an optimum amount of water for a given soil and

compaction process, which give rise to maximum dry density.

Compaction of clay,clay-lime and clay-flyash mixtures were carried out

using standard proctor test with three layers on each 25 blows. Samples for

conducting compaction tests were prepared using moulds of dimensions 10 cm

diameter and 15 cm height. In this study, lime is added for about 10% and cured

for 3, 7, and 14 days. Also,flyash is added for about 14% and is cured for 3,7 and

14 days. The values of optimum moisture content and maximum dry density are

obtained in a plot of dry density versus moisture content.

Unconfined compression test

This test is conducted on undisturbed or remoulded cohesive soils that are

normally saturated.This test may be considered as a special case of triaxial

compression test when the confining pressure is zero and the axial compressive

stress only is applied to the cylindrical specimen. The stress may be applied and

the deformation and load readings are noted until the specimen fails. The area of

cross section of specimen for various strains may be corrected assuming that the

volume of the specimen remains constant and it remains cylindrical. The

following equations were used:

Axial strain (ε) =∆L/L0

L0=initial length of sample (cm)

Corrected area of cross section (A) =A0/1-ε

A0=initial area of cross section of the sample (cm2)

Axial stress (qu) =P/A (kg/cm2)

P=axial load (kg)

Graphs are plotted between axial strain(ε) Vs axial stress(qu),% of flyash

and lime Vs axial stress and curing period VS axial stress. The maximum value of

axial stress is the unconfined compressive strength of soil sample.

Samples for conducting unconfined compression test were prepared using

moulds of dimensions 10cm diameter, 20cm height. Soil sample without additives

were tested to find out the optimum moisture content based on compressive stress.

In this study flyash is added in 12% and 14% and lime 5% and 10% respectively.

The stress is applied and the deformation and load readings are noted until

the specimen fails. The maximum axial strain is noted.

California bearing strength

Califonia state highway department developed the California bearing ratio

test ,(CBR)test in 1938 for evaluating soil subgrade and base course materials for

flexible pavements. Just after World War 2,the U.S corps of Engineers adopted

the CBR test for use in designing base courses for airfield pavements.

California bearing ratio(CBR) is the ratio of force per unit area required to

penetrate a soil mass with a standard circular piston at the rate of 1.25 mm/min to

that required for corresponding penetration in the standard material. Load that has

been obtained from the test in crushed stone(Standard material) is called standard

load. The standard material is said to have a CBR value of 100%.Smooth curves

are plotted between penetration (mm) Vs load (kg).The curve in most cases is

concave upwards in the initial portions.A correction is applied by drawing a

tangent to the curve at the point of greatest slope from the corrected load

penetration graph obtained the loads at 2.5mm and 5mm penetration. The standard

loads for these penetrations can be taken from he table below:

Standard loads for CBR tests

Penetration depth (mm) Standard load (kg) Unit load (kg/cm2)

2.5 1370 70

5.0 2055 105

7.5 2630 134

10 3180 162

12.5 3600 183

CBR value= (Test load/Standard load) X100

Samples for conducting CBR tests were prepared using moulds of

dimensions 15cm diameter and 17.5cm height. The weight of soil used is 5kg

passing through 20mm sieve. The samples were prepared at OMC and varying

lime and flyash.In this study, lime is added at 10% and fly ash at 14%.

Direct shear test

The shear strength of a soil is its maximum resistance to shear stresses just before

the failure. Shear failure of a soil mass occurs when the shear stresses induced due

to the applied compressive loads exceed the shear strength of the soil. Failure in

soil occurs by relative movements of the particles and not by breaking of particles.

Shear strength is the principal engineering property which controls the stability of

the soil mass under loads. Shear strength determines bearing capacity of soils,

stability of slopes of soils, earth pressure against retaining structure etc.

Direct shear test is conducted on a soil specimen in a shear box which can split into

two equal halves and is covered with porous grid plates on either sides. Normal

load is applied for a constant stress and shear load is applied at a constant rate of

0.02 mm/minute. The test is repeated for different stress and failure stress is noted.

A failure envelope is obtained by plotting shear stress with different normal stress

and is joined to form a straight line from which angle of shear resistance and

cohesion is obtained.

Specific gravity

The specific gravity of solid particles is defined as the ratio of the mass of a given

volume of solids to the mess of an equal volume of water at 40C. Specific gravity

of normal soils is between 2.65 to 2.80. Specific gravity of soil mass indicates the

average value of all the solid particles present in the soil mass. Also it is an

important parameter used for the determination of void ratio and particle size.

Consistency limits

The consistency of fine grained soil is the physical state in which it exists. It is

used to denote the degree of firmness of soil. The water content at which soil

changes from one state to another is known as consistency limits.

A soil containing high water is in the liquid state. It has no shear resistance

and can flow like liquid. Therefore the shear strength is equal to zero. As the water

content is reduced, the soil becomes stiffer and starts developing resistance to shear

deformation. The water content at which soil changes from liquid state to plastic

state is known as liquid limit. The liquid limit is find out by Casagrande’s liquid

limit device. The number of blows of this device is find out at different water

content. Flow curve is plot with number of blows on x axis and water content on y

axis. The water content corresponding to 25 blows is the liquid limit.

Plastic limit is the water content below which the soil stop behaving as a plastic

material. It begins to crumble when rolled into a thread of soil of 3mm diameter.

At this water content , the soil loses its plasticity and passes to the semi-solid state.

The shear strength at the plastic limit ,is about 100 times that at the liquid limit.

CHAPTER 4

RESULTS AND DISCUSSIONS

The following chapter covers the results of the testing programmes. The

results that are presented include soil properties admixture percentages and the

various testing results for the soil additive combinations .

Native soil properties and admixture percentages

Soil chacterstics were determined using atterberg limits ,hydrometer

analysis, specific gravity, standard proctor compaction and unconfined

compression tests. The test results is shown the table

Sl No: Properties Values

1 CBR value 4.3%

2 Max.dry density 1517 kg/m3

3 Optimum moisture

content

20%

4 Liquid limit 36%

5 Plastic limit 26%

6 Plasticity index 10

The grain size dirtribution curve for the soil used is shown in figure.

0.001 0.01 0.10

20

40

60

80

100

120

Particle size distribution for clayey soil

per

cen

tage

pas

sin

g (%

)

The percentage of lime and fly ash for stabilization is determined from the

unconfined compression test. The test results are shown.

400

1950

2250

18001950

native soil lime 5% lime 10% fly ash 12% flyash 14%

The native soil has an unconfined compression of 400kpa. This increased by the

addition of lime and fly ash. The maximum strength is obtained by the addition of

10% lime and 14% fly ash.

Atterberg limits

The atterberg limit test results with various soil additive combination at different curing period are presented in the table and graphs showing variation of atterberg limits with curing period is plotted for different soil-additive combination.

Atterberg test results on clay-flyash-lime mixture

Curing period Liquid limit Plastic limit Plasticity indexNative soil 36 26 10

Lime:3 days 25 15 107 days 23 18 1014 days 22 20 5

Flyash:3 days 35 19 167 days 35 23 1214 days 35 26 9

2 4 6 8 10 12 14 160

5

10

15

20

25

30

liquid limit

plastic limit

plastcity index

curing period (days)

wat

er c

onte

nt

(%)

clay-lime mixture

2 4 6 8 10 12 14 160

5

10

15

20

25

30

35

40

liquid limit

plastic limit

plasticity index

wat

er c

onte

nt

(%)

clay-fly ash mixture

The native liquid limit and plasticity index of the soil were 36 and 10. The PI

values were reduced when they are mixed with small amout of lime and became

nonplastic with the addition of more lime.For clay-lime mixture, the 3 day liquid

limit is 25, it reducese to 23 for 7days and it becomes 22 at 14days. The plastic

limit is increases from 15 at 3day to 20 at 14 days.As the liquid limit decreases and

plastic limit increases the plasticity index decreases from 10 to 5 with curing

period.

For fly ash had more limited effect on the plasticity ofthese soils.The liquid limit

remains constant with curing period for the fly ash-clay mixture.The plastic limit

increases from 19 at 3day to 26 at 14days, as a liquid limit remains constant and

plastic limit increases, the plasticity index values decreases from 16 at 3days to 9 at

14 days.

MAXIMUM DENSITY AND OPTIMUM MOISTURE CONTENT

Optimum moisture content and maximum density for native soil and each of the

soil additive combination at different curing period is presented in the table and the

variation of maximum density and optimum moisture content is plotted

Sl no: Water content Dry density

118 1490

220 1517

322 1467

424 1427

Moisture-density relationship for clay-flyash mixtures

3 days curing 7 days curing 14 days curing

Water

content

Dry density Water

content

Dry density Water

content

Dry density

17.1 1370 14.8 1260 13.3 900

17.6 1420 15.3 1300 14 1130

18.9 1490 16 1350 14.9 1000

20.1 1380 17.2 1310 15.6 870

20.5 1360 18 1250 15.9 900

0 5 10 15 20 25 30 35 400

500

1000

1500

2000

2500

native soilflyash 3daysflyash 7daysflyash14daysZAV

water content(%)

dry

dens

ity(k

g/cm

3)

moisture-density relationship for flyash clay mixture

Moisture-density relationship of clay-lime mixtures

3 days curing 7 days curing 14 days curing

Water

content

Dry density Water

content

Dry density Water

content

Dry density

22 450 24 390 24 150

23 590 25 410 26 200

24 645 26 445 28 235

25 555 27 390 30 200

26 490 28 300 32 159

0 5 10 15 20 25 30 35 400

500

1000

1500

2000

2500

native soillime 3 dayslime 7 dayslime 14 daysZAV

water content(%)

moisture-density relationship for lime-clay mixture

The maximum density and optimum moisture content for the native soil are

1517 kg/m3 and 20%. When mixed with fly ash the optimum moisture content

and the maximum density is decreased.The maximum density is 1490 kg/m3 at an

optimum moisture content of 18.9 % at 3 days.It is reduces to 1000kg/m3 at an

optimum content of 14.9% in 14 days. So both the maximum density and

optimum moisture content decreases for fly ash-clay mixture.

When mixed with lime, the optimim moisture content is increased and the

maximum dry density is decreased.The maximum density is 645 kg/m at an

optimum moisture content of 24% in 3 days.In 7days the maximum density is

445 kg/m3 at an optimum moisture content of 26%.The maximum density is

decreased to 235 kg/m3 and optimum moisture content increased to 28%.

DIRECT SHEAR TEST-FLYASH

3 days curing

7 days curing

14 days curing

Normal stress (kg/cm2)

Shear stress (kg/cm2)

Shear stress (kg/cm2)

Shear stress (kg/cm2)

Native soil0.5 0.4971 0.7891.5 0.99Lime:0.5 0.569 .72 0.991 .897 1.074 1.241.5 1.2 1.33 1.45Fly ash:0.5 0.569 0.581 0.6951 0.91 0.998 1.011.5 1.07 1.264 1.314

0.4 0.6 0.8 1 1.2 1.4 1.60

0.2

0.4

0.6

0.8

1

1.2

1.4

3 days curing7 days curing14 days curingNative soil

shea

r str

ess

(kg/

cm2 )

direct shear test: fly ash

0.4 0.6 0.8 1 1.2 1.4 1.60

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

3 days curing

7 days curing

14 days curing

Native soil

normal stress (kg/cm2)

shea

r st

ress

(k

g/cm

2)

The direct shear stresses of native soil for normal stress 0.5 kg/cm2 is

0.497kg/cm2.When mixed with fly ash the direct shear stress increases to 0.569 for

3days curing, 0.581 for 7days curing and 0.695 kg/cm2 for 14days curing.

When mixed with lime, the direct shear stress increases to 0.569 for 3days

curing, 0.72 for 7days curing and 0.99kg/cm2 for 14 days curing.

CALIFORNIA BEARING RATIO TEST

Load penetration graph for native soil is given below:

CBR:Load –penetration graph for clay-flyash mixtures:

Penetration (mm) Load (kg)

0 00.5 3.391 8.48

1.5 21.22 38.16

2.5 59.363 69.5364 82.2565 86.496

7.5 107.69610 117.872

12.5 124.656

Penetration(mm)

Load(kg)

3 days curing 7 days curing 14 days curing

0 0 0 0

0.54.01 5.55 7.93

19.35 13.86 25.99

1.522.54 25.99 33.92

240.98 53.01 63.98

2.562.77 71.85 84.82

376.89 90.92 97.92

489.99 97.96 117.84

595.99 104 122.95

7.5115.98 129.03 153.97

10126.73 141.93 164.78

12.5132.89 152.94 185.72

0 2 4 6 8 10 12 140

20

40

60

80

100

120

140

160

180

200

clay-fly ash mixture

3 days curing7 days curing14 days curingnative soil

penetration (mm)

load

(k

g)

CBR test values for clay-lime mixture

Penetration(mm)

Load(kg)

3 days curing 7 days curing 14 days curing

00 0 0

0.54.24 6.98 9.36

110.35 15.65 21.28

1.525.88 28.99 34.76

246.92 54.74 65.96

2.573.689 79.05 87.99

389.82 95.77 100.01

495 99.95 119.76

597.51 109.59 124.82

7.5125.62 134.98 154.87

10131.06 149.65 170.21

12.5140.69 156.32 190.97

0 2 4 6 8 10 12 140

50

100

150

200

250

3 days curing7 days curing14 days curingnative soil

penetration (mm)

load

(k

g)

clay-lime mixture

CHAPTER 5

CONCLUSION