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 antistripping 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: 1
Properties CBR value
Values 4.3%
2
Max.dry density
3
Optimum moisture
1517 kg/m3 20%
content 4
Liquid limit
36%
5
Plastic limit
26%
6
Plasticity index
10
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
1
CBR value
2
Max.dry density
3
Optimum moisture
Values 4.3% 1517 kg/m3 20%
content 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.
The percentage of lime and fly ash for stabilization is determined from the unconfined compression test. The test results are shown.
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 index
Native soil
36
26
10
Lime:3 days
25
15
10
7 days
23
18
10
14 days
22
20
5
Flyash:3 days
35
19
16
7 days
35
23
12
14 days
35
26
9
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
1
18
1490
2
20
1517
3
22
1467
4
24
1427
Moisture-density relationship for clay-flyash mixtures 3 days curing Water
Dry density
content 17.1
7 days curing Water
Dry density
content 1370
14.8
14 days curing Water
Dry density
content 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
Moisture-density relationship of clay-lime mixtures 3 days curing Water
Dry density
content
7 days curing Water
Dry density
content
14 days curing Water
Dry density
content
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
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
Normal stress (kg/cm2)
3 days curing
7 days curing
14 days curing
Shear stress (kg/cm2)
Shear stress (kg/cm2)
Shear stress (kg/cm2)
Native soil 0.5
0.497
1
0.789
1.5
0.99
Lime: 0.5
0.569
.72
0.99
1
.897
1.074
1.24
1.5
1.2
1.33
1.45
Fly ash:
0.5
0.569
0.581
0.695
1
0.91
0.998
1.01
1.5
1.07
1.264
1.314
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:
Penetration (mm)
Load (kg)
0 0.5 1 1.5 2
38.16
2.5
59.36
3
69.536
4
82.256
5
86.496 CBR:Load –penetration graph for clay-
7.5
107.696 flyash mixtures:
10
117.872 Load(kg) 124.656
Penetration(mm) 12.5
3 days curing
7 days curing
0
0
0
0
0.5
4.01
5.55
7.93
1
9.35
13.86
25.99
1.5
22.54
25.99
33.92
2
40.98
53.01
63.98
2.5
62.77
71.85
84.82
3
76.89
90.92
97.92
4
89.99
97.96
117.84
5
95.99
104
122.95
7.5
115.98
129.03
153.97
10
126.73
141.93
164.78
12.5
132.89
152.94
185.72
CBR test values for clay-lime mixture Load(kg) Penetration(mm) 3 days curing
7 days curing
0
0
0
0
0.5
4.24
6.98
9.36
1
10.35
15.65
21.28
1.5
25.88
28.99
34.76
2
46.92
54.74
65.96
2.5
73.689
79.05
87.99
3
89.82
95.77
100.01
4
95
99.95
119.76
5
97.51
109.59
124.82
7.5
125.62
134.98
154.87
10
131.06
149.65
170.21
12.5
140.69
156.32
190.97
CHAPTER 5
CONCLUSION
