Stabilization of Black Cotton Soil

A PROJECT REPORT ON

STABILIZATION OF BLACK COTTON SOIL (SUBGRADE SOIL) USING LIME AND FLY ASH SUBMITTED BY SOMDATT DAHIYA 09EELCE055 IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE DEGREE OF BACHELOR OF TECHNOLOGY IN CIVIL ENGINEERING OF GOVT. ENGINEERING COLLEGE, BHARATPUR, RAJASTHAN UNDER THE GUIDANCE OF Dr. BISWJIT ACHARYA

DEPARTMENT OF CIVIL ENGINEERING GOVT. ENGINEERING COLLEGE, BHARATPUR, RAJASTHAN 2012-2013

Stabilization of black cotton soil using lime and fly ash

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CERTIFICATE This is to certify that, the project entitled STABILIZATION OF BLACK COTTON SOIL (SUBGRADE SOIL) USING LIME AND FLY ASH Submitted by Mr. SOMDATT DAHIYA Is a record of his own work carried out by him in partial fulfillment for the award of BACHELOR OF TECHNOLOGY IN CIVIL ENGINEERING Govt. engineering college, Bharatpur, rajasthan Under my guidance during the academic year 2012-2013 Date : Place:BHARATPUR

Dr. Biswajit Acharya

Er. Amit Daiya

(ProjectGuide)

(H.O.D)

DEPARTMENT OF CIVIL ENGINEERING GOVT. ENGINEERING COLLEGE, BHARATPUR 2012-2013 GEC BHARATPUR

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Acknowledgement When we take a glance over our journey throughout the year, few respectful and friendly faces and encouragement come across our mind. What we remember the most is the immense help, guidance and teachings of our project guide Dr. Biswajit Acharya without whom working in this project would have been walking on an unknown path. He who has taken sincere efforts to lead us, he who taught us how to plan, work and analyze and he who made us discover our hidden qualities will be always remembered by us for the teachings and principles he taught us during the project course. We would like to thank him for being such an excellent teacher, a perfect guide, a strict disciplinarian, an indefatigable leader and a true friend. We are grateful to Er. Priyanka Gupta for their timely and valuable guidance. We are grateful for the guidance and kind support of our H.O.D, Er. Amit Daiya. We would like to extend our gratitude towards the supporting staff for being very helpful. We are very grateful to those who in the form of books had conveyed guidance in this project work. At last, we would like to thank our friends and family for their support and encouragement throughout the year.

Mr. SOMDATT DAHIYA B.Tech. civil

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Abstract From the recent past years people are facing the problems on construction of road on black cotton soil. In construction of roads on BC soils, the behavior of soils with respect to water poses a big problem. The soil undergoes high swelling shrinkage and has poor subgrade strength. Stabilization of sub grade soil helps to achieve required strength of subgrade, eliminate the associated problems and this reduces the thickness of pavement. Our project aims to stabilize black cotton soil using fly ash and lime mixture; thus the project work includes finding optimum proportion of soil, fly ash, lime mixture which is acceptable, applicable and economical.

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INDEX

CHAPTER CHAPTER NAME NO.

1.

INTRODUCTION

CONTENTS

1.1 Introduction of the project

PAGE NO.

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2.1 black cotton soil 2.2 problems associated with black cotton soil 2.3 stabilization of soil 2.

LITERATURE REVIEW

2.4 lime stabilization 11 2.5 fly ash stabilization 2.6 lime + different materials for stabilization 2.7 lime + fly ash stabilization 2.8 Materials and their types

3.

OBJECTIVES OF THE PROJECT

3.1 objectives of the project

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4.1 properties of local soil METHODOLOGY 4.2 preparation of samples for tests 4.

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4.3 curing of samples 4.4 testing of samples

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5.1 Preliminary observations and readings 5.1.1 Properties of black cotton soil 5.1.2 Unconfined compressive strength tests results of different proportions 5.1.3 Effect on strength when fly ash is varied keeping lime constant 5.1.4 Effect on strength when lime is varied keeping fly ash constant 5.1.5 Effect of curing time on the strength of the sub grade 5.1.6 Discussions about the preliminary reading 5.2 Final Observation and readings

5.

RESULTS AND DISCUSSIONS

5.2.1 Variation in compressive strength with variation in fly ash (explained using bar chart)

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5.2.2 Variation in compressive strength with variation in lime (explained using bar chart) 5.2.3 Variation in compressive strength with variation in fly ash (explained using line graphs) 5.2.4 Variation in compressive strength with variation in lime (explained using line graphs) 5.2.5Discussions about the final readings obtained: 5.2.6Properties of black cotton with12% lime and 30% fly ash

soil

5.5.7 Comparison between black cotton soil with no stabilizer and black cotton soil added with 12% lime and 30% fly ash GEC BHARATPUR

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6.1 Explanation of the derivation of formula 6.

APPLICATION FORMULA

7.

CONCLUSIONS

6.2 Step wise procedure for calculating the percentage of lime and fly ash required for stabilization of any black cotton

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7.1 conclusion 72 7.2 future scope of project 8.1 Books 8.

REFERENCES

75 8.2 Technical research papers

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Chapter 1 INTRODUCTION

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INTRODUCTION Road needs good quality paving material having adequate strength and durability characteristics. Subgrade soil is an integral part of the road pavement from beneath. The subgrade soil and its properties are important in the design of pavement structure. The main function of the subgrade is to give support to the pavement. And for this, the subgrade should possess sufficient stability under adverse climate and loading condition. In developing countries like India the biggest handicap to provide a complete network of road system is its limited financial availability to build road by the conventional methods. The soils of north india are residual, derived from the underlying basalts. In the semi-dry plateau, the regular (black-cotton soil) is clayey, rich in iron, but poor in nitrogen and organic matter; it is moisture-retentive.

Therefore, there is a need to resort to one of the suitable methods of low cost road construction. Under this circumstance use of locally available material after suitable treatment is only solution to meet the growth demand of road constructions. The construction cost can be considerably decreased by selecting local materials including local soils for the construction of the lower layers of the pavement. If the stability of the local soil is not adequate for supporting wheel loads, the properties can be improved by soil stabilization techniques. The principle of soil stabilized road construction involves the effective utilization of local soil and other suitable stabilizing agent. Therefore the first and foremost task is to characterize the locally available soil and after proper assessment, suitable treatment is to be provided, if required. Soil stabilization is any process which improves the physical properties of a soil, such as increasing the shear strength, bearing capacity and the resistance to erosion, dust formation, or frost heaving. The stabilization methods used are divided into mechanical, chemical, and electrochemical methods. Mechanical methods are those in which the compaction

or

bulk

density

is

increased

by

dynamic

or

vibro-

compaction. Electrochemical methods of stabilization involve the reduction of water content by electro-osmosis. Chemical stabilization is one of the effective stabilization techniques.

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Chapter 2 LITERATURE REVIEW

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2.1 Black cotton soil Black cotton soils are inorganic clays of medium to high compressibility and form a major soil group in Maharashtra. They are characterized by high shrinkage and swelling properties. Because of its high swelling and shrinkage characteristics, the Black cotton soil has been a challenge to the highway engineers. The Black cotton soil is very hard when dry, but loses its strength completely when in wet condition. It is observed that on drying, the black cotton soil develops cracks of varying depth. As a result of wetting and drying process, vertical movement takes place in the soil mass. All these movements lead to failure of pavement, in the form of settlement, heavy depression, cracking and unevenness.

The roads laid on Black cotton soil (BC soil) bases develop undulations at the road surface due to loss of strength of the sub grade through softening during monsoon. Around 40 to 60% of the Black cotton soil (BC soil) has a size less than 0.001 mm. At the liquid limit, the volume change is of the order of 200 to 300% and results in swelling pressure as high as 8 kg/cm2/ to 10 kg/cm2. As such Black cotton soil (BC soil) has very low bearing capacity and high swelling and shrinkage characteristics. Due to its peculiar characteristics, it forms a very poor foundation material for road construction. Soaked laboratory CBR values of Black Cotton soils are generally found in the range of 2 to 4%. Due to very low CBR values of Black cotton soil (BC soil), excessive pavement thickness is required for designing for flexible pavement.

Prof. katti has studied 13 black cotton soils, most of them from Maharashtra state. The studies conducted on these soils were consistency, density, swelling pressure, consolidation, shear, permeability, thixotropic property and effect of inorganic chemicals etc.

2.2 Problems associated with black cotton soil as subgrade There are two major problems associated with black cotton soil viz problems arising due to water saturation and design problems in black cotton soil. They are described below. A) Problems Arising out of Water Saturation GEC BHARATPUR

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It is a well-known fact that water is the worst enemy of road pavement, particularly in expansive soil areas. Water penetrates into the road pavement from three sides viz. top surface, side berms and from sub grade due to capillary action. It has been found during handling of various road investigation project assignments for assessing causes of road failures that water has got easy access into the pavement. It saturates the sub grade soil and thus lowers its bearing capacity, ultimately resulting in heavy depressions and settlement. In the base course layers comprising of Water Bound Macadam (WBM), water lubricates the binding material and makes the mechanical interlock unstable. In the top bituminous surfacing, raveling, stripping and cracking develop due to water stagnation and its seepage into these layers.

B) Design Problems in Black cotton soils

In India, CBR method developed in USA is generally used for the design of crust thickness. This method stipulates that while determining the CBR values in the laboratory and in the field, a surcharge weight of 15 kg and 5 kg per 62 mm and 25 mm thickness respectively should be used to counteract the swelling pressure of Black cotton soils (BC soils). BC soils produce swelling pressure in the range of 20-80 tons/m2 and swelling in the range of 10-20%.Therefore, CBR values obtained are not rational and scientific modification is required for determining CBR values of expansive soil. Having heavy-duty traffic of 4500 commercial vehicles per day as generally found on our National Highways and taking CBR value of 2%, total crust thickness of flexible pavement works out to 830 mm which is practically an impossible preposition. It is felt that CBR design curves require modification for expansive soils. If heavy traffic intensity of 4500 commercial vehicles per day is assumed, crust thickness of rigid pavement works out approximately 300-320 mm, which is about one third of thickness needed for flexible pavement.

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2.3 Stabilization of subgrade soil Soil stabilization is any process which improves the physical properties of a soil, such as increasing the shear strength, bearing capacity and the resistance to erosion, dust formation, or frost heaving. The stabilization methods used are divided into mechanical, chemical, and electrochemical methods. Mechanical methods are those in which the compaction

or

bulk

density

is

increased

by

dynamic

or

vibro-

compaction. Electrochemical methods of stabilization involve the reduction of water content by electro-osmosis. Chemical stabilization is one of the effective stabilization techniques. 2.4 Lime stabilization Several investigations were done to evaluate the soil stabilization process using lime [either CaO or Ca(OH)2]. Lime stabilization involves the formation of strong bonds between the clay minerals and other soil particles and is therefore ineffective in granular soils. Three processes appear to be operative: (1) rapid replacement of exchangeable cations by calcium with increased interparticle bonding and a more flocculated fabric; (2) slower attack on the edges of the clay minerals by alkaline solutions in which the solubility of silicon is increased, with the possible formation of new silicates similar to those in cement; and (3) crystallization of calcite to form additional interparticle bridges. Prof katti studied the effect of lime on unconfined compressive strength of 13 black cotton soils and found that the optimum lime content for various soils fell in the range of 4 to 10 % and appeared to shift to higher percentages with an increase in curing time. A 2 to 4 % addition of lime produced little gain in strength over time. According to Dr. K. R. Arora, the amount of lime required for stabilization varies between 2 to 10 % of the soil. He has stated the following amount as a rough guide (i) 2 to 5 % for clay gravel material having less than 50% of silt clay fraction (ii) 5 to 10% for soil with more than 50% of silt – clay fraction (iii)For soil having particle size intermediate between (i) and (ii) above, the quantity of lime required is between 3 to 7% (iv) About 10 % for heavy clays used as bases and sub bases.

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2.4.1 Qubain et al. (2000) incorporated the benefits of sub-grade lime stabilization, for the first time, into the design of a major interstate highway pavement in Pennsylvania. The project comprised widening and complete reconstruction of 21 Km of the Pennsylvania turnpike in somerset-county. Field explorations indicated that the sub-grade is fairly homogeneous and consists primarily of medium to stiff clayey soils. To safeguard against potential softening due to rain, lime modification has been traditionally utilized as a construction expedience for highway project with clayey sub-grade. Lime improves the strength of clay by three mechanisms: hydration, flocculation, and cementation. The first and second mechanisms occur almost immediately upon introducing the lime, while the third is a prolonged effect. Qubain et al. investigated the first and second mechanisms. Laboratory tests were performed to accurately capture the immediate benefits of lime stabilization for design. Both treated and natural clayey samples were subjected to resilient modulus and California bearing ratio testing. To prevent cementation, the limetreated specimens were not allowed to cure. Nevertheless, they showed significant increase in strength, which, when incorporated into design, reduced the pavement thickness and resulted in substantial savings.

2.4.2 Weber (2001) investigated the effect of both curing (storage) and degree of compaction on the loss loam stabilized using different additives. He obtained the best results under condition of moisture atmosphere storage. At the water storage condition, the tempering of the stabilized specimens delayed due to the changing of pH-value in the pores water. The reactivity of lime stabilized specimens was continuing under this water storage condition. He noticed that the variation of compaction degree of the stabilized specimens affected on the behavior of the stabilized specimens and the compaction at the highest densities lead to brittle failure behavior.

2.4.3 Ismail (2004) studied materials and soils derived from the Feuerletten (Keuper) and Amaltheenton (Jura) formations along the new Nuernberg-Ingolstadt railway line (Germany). His work included petrological, mineralogical studies and scanning electron microscope analysis. Ismail treated and stabilized these materials related to road construction using lime (10%), cement (10%), and lime/cement (2.5%/7.5%). He determined consistency GEC BHARATPUR

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limits, compaction properties, and shear- and uniaxial-strength. Ismail concluded that by increasing the optimum moisture content (%) of the treated soils mixtures, the maximum dry density decreased. The cohesion and the friction angle of the improved materials increased for all the treated mixtures. In case of the lime-treated materials, the cohesion decreased by curing time. For Feuerletten materials, uniaxial strength increased strongly using lime and cement together. For Amaltheenton, uniaxial strength increased strongly with cement alone. He also noticed that the loss of weight during freezing and thawing test was low and depended on the material type.

2.4.4 Ampera & Aydogmust (2005) treated Chemnitz clayey soil [according to American Association of State Highway and Transportation Officials (AASHTO)] using lime (2, 4, and 6%) and cement (3, 6, and 9%). They conducted compaction, unconfined compressive strength, and direct shear tests on untreated and treated specimens. They concluded that the strength of cement treated soil was generally greater than the strength of lime treated soil. They also reported that lime stabilization is more suitable for the clayey soils. The relationships determined from direct shear tests were similar to those determined from unconfined compressive strength tests. Thus, the results of shear strength tests showed a similar trend to that of the unconfined compressive strength tests. 2.4.5 Venkata Swamy, B studied on Stabilisation of Black Cotton Soil by Lime Piles. Lime stabilization of clays in field is achieved by shallow mixing of lime and soil or by deep stabilization technique. Shallow stabilization involves scarifying the soil to the required depth and lime in powder or slurry form is spread and mixed with the soil using a rotovator. The use of lime as deep stabilizer has been mainly restricted to improve the engineering behaviour of soft clays Deep stabilization using lime can be divided in three main groups: lime columns, lime piles and lime slurry injection. 2.5 Fly ash stabilization Various studies were carried out in several countries like USA, Japan, India, etc to verify the soil stabilization process using fly ash either class F or class C and other off specification= types of fly ash. Some Fly ash by itself has cementatious value but in the presence of moisture it reacts chemically and forms cementatious compounds and attributes to the improvement of strength and compressibility characteristics of soils. It GEC BHARATPUR

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has a long history of use as an engineering material and has been successfully employed in geotechnical applications.

2.5.1Edil et al. (2002) conducted a field evaluation of several alternatives for construction over soft sub-grade soils. The field evaluation was performed along a 1.4 Km segment of Wisconsin state highway 60 and consisted of several test sections. By products such as fly ash, bottom ash, foundry slag, and foundry sand were used. A class C fly ash was used for one test section. Unconfined compression testing showed that 10% fly ash was sufficient to provide the strength necessary for the construction on the sub-grade. Data were obtained before and after fly ash placement by testing undisturbed samples in the laboratory and by using a soil stiffness gauge (SSG) and a dynamic cone penetrometer (DCP) in the field. Unconfined compressive strength, soil stiffness, and dynamic cone penetration of the native soil before fly ash placement ranged between 100 - 150 KPa, 4 8 MN/m², and 30 -90 mm/blow, respectively. After fly ash addition, the unconfined compressive strength reached as high as 540 KPa, the stiffness ranged from 10 to 18 MN/m2, and the Dynamic Penetration Index (DPI) was less variable and ranged between 10 and 20 mm/blow. CBR of 32% was reported for the stabilized sub-grade, which is rated as “good” for sub-base highway construction. CBR of the untreated sub-grade was 3%, which is rated as “very poor”.

2.5.2 Acosta et al. (2002) estimate the self-cementing fly ashes as a sub-grade stabilizer for Wisconsin soils. A laboratory-testing program was conducted to evaluate the mechanical properties of fly ash alone, and also to evaluate how different fly ashes can improve the engineering properties of a range of soft sub-grade soil from different parts of Wisconsin. Seven soils and four fly ashes were considered for the study. Soil samples were prepared with different fly ash contents (i.e., 0, 10, 18, and 30%), and compacted at different soil water contents (optimum water content, 7% wet of optimum water content “approximate natural water content of the soil”, and a very wet conditions “9 to 18% wet of optimum water content”). Three types of tests were performed: California bearing ratio test, resilient modulus test, and unconfined compressive strength test. The soils selected represented poor sub-grade conditions with CBR ranging between 0 and 5 in their natural GEC BHARATPUR

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condition. A substantial increase in the CBR was achieved when soils were mixed with fly ash. Specimens prepared with 18% fly ash content and compacted at the optimum water content show the best improvement, with CBR ranging from 20 to 56. Specimens prepared with 18% fly ash and compacted at 7% wet of optimum water content showed significant improvement compared to the untreated soils, with CBR ranging from 15 to 31 (approximately an average CBR gain of 8 times). On the other hand, less improvement was noticed when the specimens were prepared with 18% fly ash and compacted in very wet condition (CBR ranging from 8 to 15). Soil-fly ash mixtures prepared with 18% fly ash content and compacted at 7% wet of optimum water content had similar or higher modulus than untreated specimens compacted at optimum water content. Resilient modulus of specimens compacted in significantly wet conditions, in general, had lower module compared to the specimen compacted at optimum water content. The resilient modulus increased with increasing the curing time. The resilient modulus of specimens prepared at 18% fly ash content and compacted at 7% wet of optimum water content was 10 to 40% higher after 28 days of curing, relative to that at 14 days of curing. Unconfined compressive strength of the soilfly ash mixtures increased with increasing fly ash content. Soil-fly ash specimens prepared with 10 and 18% fly ash content and compacted 7% wet of optimum water content had unconfined compressive strength that were 3 and 4 times higher than the original untreated soil specimen compacted at 7% wet of optimum water content. CBR and resilient modulus data was used for a flexible pavement design. Data developed from stabilized soils showed that a reduction of approximately 40% in the base thickness could be achieved when 18% fly ash is used to stabilize a soft subgrade. 2.5.3 Şenol et al. (2002) studied the use of self-cementing class C fly ash for the stabilization of soft sub-grade of a city street in cross plains, Wisconsin, USA. Both strength and modulus based approaches were applied to estimate the optimum mix design and to determine the thickness of the stabilized layer. Stabilized soil samples were prepared by mixing fly ash at three different contents (12, 16, and 20%) with varying water contents. The samples were subjected to unconfined compression test after 7 days of curing to develop water content strength relationship. The study showed that the engineering properties, such as unconfined compressive strength, CBR, and resilient GEC BHARATPUR

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modulus increase substantially after fly ash stabilization. The stabilization process is construction sensitive and requires strict control of moisture content. The impact of compaction delay that commonly occurs in field construction, was evaluated, one set of the samples was compacted just after mixing with water, while the other set after two hours. The results showed that the strength loss due to compaction delay is significant and, therefore, must be considered in design and construction. CBR and resilient modulus tests were conducted and used to determine the thickness of the stabilized layer in pavement design.

2.5.4 Thomas & White (2003) used self-cementing fly ashes (from eight different fly ash sources) to treat and stabilize five different soil types (ranging from ML to CH) in Iowa for road construction applications. They investigated various geotechnical properties (under different curing-conditions) such as compaction, qu-value, wet/dry and freeze/thaw durability, curing time effect, and others. They reported that Iowa selfcementing fly ashes can be an effective means of stabilizing Iowa soil. Unconfined compressive strength, strength gain, and CBR-value of stabilized soils increased especially with curing time. Soil-fly ash mixtures cured under freezing condition and soaked in water slaked and were unable to be tested for strength. They also noticed that stabilized paleosol exhibited an increase in the freeze/thaw durability when tested according to ASTM C593, but stabilized Turin loess failed in the test.

2.5.5 Effect of Fly ash on expansive soil was studied by Erdal Cokca. Fly ash consists of often hollow spheres of silicon, aluminium and iron oxides and unoxidized carbon. There are two major classes of fly ash, class C and class F. The former is produced from burning anthracite or bituminous coal and the latter is produced from burning lignite and sub bituminous coal. Both the classes of fly ash are puzzolans, which are defined as siliceous and aluminous materials. Thus Fly ash can provide an array of divalent and trivalent cations (Ca2+, Al3+, Fe3+etc) under ionized conditions that can promote flocculation of dispersed clay particles. Thus expansive soils can be potentially stabilized effectively by cation exchange using fly ash. He carried out investigations using Soma Fly ash and Tuncbilek fly ash and added it to expansive soil at 0-25%. Specimens with fly ash were cured for 7days and 28 days after which they were subjected to Oedometer free GEC BHARATPUR

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swell tests. And his experimental findings confirmed that the plasticity index, activity and swelling potential of the samples decreased with increasing percent stabilizer and curing time and the optimum content of fly ash in decreasing the swell potential was found to be 20%. The changes in the physical properties and swelling potential is a result of additional silt size particles to some extent and due to chemical reactions that cause immediate flocculation of clay particles and the time dependent puzzolanic and self hardening properties of fly ash and he concluded that both high –calcium and low calcium class C fly ashes can be recommended as effective stabilizing agents for improvement for improvement of expansive soils.

2.5.6 Pandian et.al. (2002) studied the effect of two types of fly ashes Raichur fly ash (Class F) and Neyveli fly ash (Class C) on the CBR characteristics of the black cotton soil. The fly ash content was increased from 0 to 100%. Generally the CBR/strength is contributed by its cohesion and friction. The CBR of BC soil, which consists of predominantly of finer particles, is contributed by cohesion. The CBR of fly ash, which consists predominantly of coarser particles, is contributed by its frictional component. The low CBR of BC soil is attributed to the inherent low strength, which is due to the dominance of clay fraction. The addition of fly ash to BC soil increases the CBR of the mix up to the first optimum level due to the frictional resistance from fly ash in addition to the cohesion from BC soil. Further addition of fly ash beyond the optimum level causes a decrease up to 60% and then up to the second optimum level there is an increase. Thus the variation of CBR of fly ash-BC soil mixes can be attributed to the relative contribution of frictional or cohesive resistance from fly ash or BC soil respectively. In Neyveli fly ash also there is an increase of strength with the increase in the fly ash content, here there will be additional puzzolonic reaction forming cementitious compounds resulting in good binding between BC soil and fly ash particles.

2.5.7 A similar study was carried out by Phanikumar and Sharma and the effect of fly ash on engineering properties of expansive soil through an experimental programme. The effect on parameters like free swell index (FSI), swell potential, swelling pressure, plasticity, compaction, strength and hydraulic conductivity of expansive soil was studied. The ash blended expansive soil with fly ash contents of 0, 5, 10, 15 and 20% on a dry GEC BHARATPUR

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weight basis and they inferred that increase in fly ash content reduces plasticity characteristics and the FSI was reduced by about 50% by the addition of 20% fly ash. The hydraulic conductivity of expansive soils mixed with fly ash decreases with an increase in fly ash content, due to the increase in maximum dry unit weight with an increase in fly ash content. When the fly ash content increases there is a decrease in the optimum moisture content and the maximum dry unit weight increases. The effect of fly ash is akin to the increased compactive effort. Hence the expansive soil is rendered more stable. The undrained shear strength of the expansive soil blended with fly ash increases with the increase in the ash content.

2.6 Lime + different materials for stabilization 2.6.1 Rice husk ash is apotentially useful waste, which can be used with lime to improve physical, engineering and strength properties of black cotton soil. The cementitious compounds formed during pozzolanic reactions acts as a bonding material for the soil particles. The plasticity characteristics of black cotton soil are improved upon addition of RHA and lime. The PI of soil decreses to 7.93 percent from 35.79 percent on addition of 10% RHA and 6% lime. With addition of RHA and lime to BC soil, the MDD decreases and OMC increases. Also, the optimum CBR was found for BC soil-10% RHA-6%lime mixes. 2.6.2 Eggshell Powder (ESP) has not been used as a stabilizing material; however, it could be a supplement for industrial lime. The effect of eggshell powder on the stabilizing potential of lime on an expansive clay soil has been studied by O.O. Amu. Tests were carried out to determine the optimal quantity of lime and the optimal percentage of limeESP combination; the optimal quantity of lime was gradually replaced with suitable amount of eggshell powder. The lime stabilized and lime-ESP stabilized mixtures were subjected to engineering tests. The optimal percentage of lime-ESP combination was attained at a 4% ESP + 3% lime, which served as a control.

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2.7 lime + fly ash stabilization Several works were done to treat and stabilize various types of the problematic soils using lime and fly ash together

2.7.1 Nalbantoglu & Gucbilmez (2002) studied the utilization of an industrial waste in calcareous expansive clay stabilization, where the calcareous expansive soil in Cyprus had caused serious damage to structures. High-quality Soma fly ash admixture has been shown to have a tremendous potential as an economical method for the stabilization of the soil. Fly ash and lime-fly ash admixtures reduce the water absorption capacity and the compressibility of the treated soils. Unlike some of the previously published research, an increase in hydraulic conductivity of the treated soils was obtained with an increase in percent fly ash and curing time. X-ray diffractograms indicate that pozzolanic reactions cause an alteration in the mineralogy of the treated soils, and new mineral formations with more stable silt-sand-like structures are produced. The study showed that, by using cation exchange capacity (CEC) values, with increasing percentage of fly ash and curing time, soils become more granular in nature and show higher hydraulic conductivity values.

2.7.2 Zhang & Cao (2002) conducted an experimental program to study the individual and admixed effects of lime and fly ash on the geotechnical characteristics of expansive soil. Lime and fly ash were added to the expansive soil at 4 - 6% and 40 - 50% by dry weight of soil, respectively. Testing specimens were determined and examined in chemical composition, grain size distribution, consistency limits, compaction, CBR, free swell and swell capacity. The effect of lime and fly ash addition on a reduction of the swelling potential of an expansive soil texture was reported. It was revealed that a change of expansive soil texture takes place when lime and fly ash are mixed with expansive soil. Plastic limit increases by mixing lime and liquid limit decreases by mixing fly ash, and this decreased plasticity index. As the amount of lime and fly ash is increased, there is an apparent reduction of maximum dry density, free swell, and of swelling capacity under 50 KPa pressure and a corresponding increase in the percentage of coarse particles, optimum moisture content, and in the CBR value. They concluded that the expansive soil can be successfully stabilized by lime and fly ash. GEC BHARATPUR

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2.7.3 Beeghly (2003) evaluated the use of lime together with fly ash in stabilization of soil subgrade (silty and clayey soils) and granular aggregate base course beneath the flexible asphalt layer or rigid concrete layer. He reported that lime alone works well to stabilize clay soils but a combination of lime and fly ash is beneficial for lower plasticity (higher silt content) soils. He noticed that both unconfined compressive strength and CBR values of treated stabilized soils (moderate plasticity “PI < 20” and high silt content “i.e. > 50%”) with lime and fly ash together are higher than the values with lime alone. Beeghly (2003) also concluded that the capillary soak of the stabilized specimens led to a loss of unconfined compressive strength (15 - 25%). Finally, lime/fly ash admixtures resulted in cost savings by increment material cost by up to 50% as compared to Portland cement stabilization.

2.7.4 Parson & Milburn (2003) conducted a series of tests to evaluate the stabilization process of seven different soils (CH, CH, CH, CL, CL, ML, and SM) using lime, cement, class C fly ash, and an enzymatic stabilizer. They determined Atterberg limits and unconfined compressive strengths of the stabilized soils before and after carrying out of durability tests (freeze/thaw, wet/dry, and leach testing). They reported that lime and cement stabilized soils showed better improvement compared to fly ash treated soils. In addition, the enzymatic stabilizer did not strongly improve the soils compared to the other stabilizing agents (cement, lime, and fly ash). 2.7.5 Faqir Chand has found that hydrated lime in the range of 5 to 8 % and fly ash between 10 to 15% brings remarkable improvement in the engineering characteristics of BC soils. However, excess of lime more than 8% reduces the strength and weakens the soil iniatial properties due to liberation of excess heat during hydration. Therefore, 6% lime is taken as optimum level of cement content with fly ash 15%. 2.7.6 Niroj Mishra has studied the engineering properties of only soil, soil + fly ash@ (20,30 and 40%), soil + lime@(2,3,4%) and soil + fly ash@(20,30%)+lime@(2,3,4%) . He observed that maximum CBR value has been obtained for 70:30:3 mix of soil, fly ash and lime

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Through our literature review, it was found that lime and fly ash alone, lime in combination with other materials and lime + fly ash can be used for subgrade stabilization. However, the study in the area of lime + fly ash stabilization is unreliable, unauthentic. Hence, there borne a need to make a extensive study on lime+fly ash stabilization.

2.8 Materials and Types

2.8.1 Lime

Lime can be used either to modify some of the physical properties and thereby improve the quality of soil or to transform the soil into a stabilized mass, which increases its strength and durability. The amount of lime additive will depend upon either the soil to be modified or stabilized. Generally, lime is suitable for clay soils with PI ≥ 20% and > 35% passing the No.200 sieve (0.074 mm). Lime stabilization is applied in road construction to improve subbase and sub-grades, for railroads and airports construction, for embankments, for soil exchange in unstable slopes, for backfill, for bridge abutments and retaining walls, for canal linings, for improvement of soil beneath foundation slabs, and for lime piles. Lime stabilization includes the use of burned lime products, quicklime and hydrated lime i.e oxides and hydroxides, respectively, or lime by-products .The improvement of the geotechnical properties of the soil and the chemical stabilization process using lime take place through two basic chemical reactions as follow: I) Short-term reactions including cation exchange and flocculation, where lime is a strong alkaline base which reacts chemically with clays causing a base exchange. Calcium ions (divalent) displace sodium, potassium, and hydrogen (monovalent) cations and change the electrical charge density around the clay particles. This results in an increase in the interparticle attraction causing flocculation and aggregation with a subsequent decrease in the plasticity of the soils. II) Long-term reaction including pozzolanic reaction, where calcium from the lime reacts with the soluble alumina and silica from the clay in the presence of water to produce stable calcium silicate hydrates (CSH), calcium aluminate hydrates (CAH), and calcium GEC BHARATPUR

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aluminosilicate hydrates (CASH) which generate long-term strength gain and improve the geotechnical properties of the soil. The use of lime for soil stabilization is either in the form of quicklime (CaO) or hydrated lime Ca(OH)2. Agricultural lime or other forms of calcium carbonate, or carbonated lime, will not provide the necessary reactions to improve sub-grade soils mixed with lime. In the present study, hydrated lime was used. Hydrated lime is calcium hydroxide, Ca (OH)2. It is produced by reacting quicklime (CaO) with sufficient water to form a white powder. This process is referred to as slaking. High calcium quicklime + water CaO + H2O

Hydrated lime + Heat

Ca(OH)2 + Heat

Hydrated lime is used in most of the lime stabilization applications. Quicklime represents approximately 10% of the lime used in lime stabilization process. Other forms of lime sometimes used in lime stabilization applications are dehydrated dolomitic lime, monohydrated dolomitic lime, and dolomitic quicklime. Calcium oxide may be more effective in some cases, however the quick lime will corrosively attack equipment. The Addition of the hydrated lime Ca(OH)2, in situ or in laboratory, is either as slurry formed by the slaking of quicklime, or as dry form. In the present study, the addition of the hydrated lime is in a dry form. In general, all lime treated fine-grained soils exhibit decreased plasticity, improved workability and reduced volume change characteristics. However, not all soils exhibit improved strength characteristics. It should be emphasized that the properties of soil-lime mixtures are dependent on many factors such as soil type, lime type, lime percentage, and curing conditions like time, temperature, and moisture.

2.8.2 Fly ash

Fly ash is a by-product of burning coal at electric power plants. It is a fine residue composed of unburned particles that solidifies while suspended in exhaust gases. Fly ash is carried off in stack gases from a boiler unit, and is collected by mechanical methods or electrostatic precipitators. Fly ash is composed of fine spherical silt size particles in the range of 0.074 to 0.005 mm. Fly ash collected using electrostatic precipitators usually has finer particles than fly ash collected using mechanical precipitators. Fly ash is one of the most useful and versatile industrial by-products. When geotechnical Engineers are faced GEC BHARATPUR

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with clayey or expansive soils, the engineering properties of those soils may need to be improved to make them suitable for construction. Waste materials such as fly ash or pozzolanic materials are a source of silica and alumina with high surface area has been used for soil improvement. Fly ash is generated in huge quantities as a by-product of burning coal at electric power plants . The potential for using fly ash in soil stabilization has increased significantly in many countries since it is environmentally safe.

Fly ash is classified into two classes: F and C. Class F fly ash which is not self-cementing fly ash is produced from burning anthracite and bituminous coals and contains small amount of lime (CaO) to produce cementitious products. An activator such as Portland cement or lime must be added. This fly ash has siliceous and aluminous material, which itself possesses little or no cementitious value but it reacts chemically with lime at ordinary temperature to form cementitious compounds. Class C fly ash which is self-cementing fly ash is produced from lignite and subbituminous coals and usually contains significant amount of lime .This type (class C) is self-cementing because it contains a high percent of calcium oxide (CaO) ranging from 20 to 30%. Formation of cementitious material by the reaction of lime with the pozzolans (Al2O3, SiO2, and Fe2O3) in the presence of water is known as hydration of fly ash. The hydrated calcium silicate or calcium aluminate as cementitious material, can join inert materials together. The pozzolanic reactions for soil stabilization are as follow : CaO + H2O Ca (OH)2

Ca(OH)2 + Heat Ca ++ + 2 (OH)

Ca ++ + 2 (OH) + SiO2 (silica) Ca ++ + 2 (OH) + Al2O3

CSH “Calcium silicate hydrate“ (gel) CAH “Calcium aluminate hydrate”

(alumina) (fibrous)

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2.8.3 Black cotton soil Black cotton soils are inorganic clays of medium to high compressibility and form a major soil group in Maharashtra. They are characterized by high shrinkage and swelling properties. Because of its high swelling and shrinkage characteristics, the Black cotton soil has been a challenge to the highway engineers. The Black cotton soil is very hard when dry, but loses its strength completely when in wet condition. It is observed that on drying, the black cotton soil develops cracks of varying depth.The roads laid on Black cotton soil (BC soil) bases develop undulations at the road surface due to loss of strength of the sub grade through softening during monsoon. Around 40 to 60% of the Black cotton soil (BC soil) has a size less than 0.001 mm. At the liquid limit, the volume change is of the order of 200 to 300% and results in swelling pressure as high as 8 kg/cm2/ to 10 kg/cm2. Average Plasticity Index of black cotton soil was found as 60 % As such Black cotton soil (BC soil) has very low bearing capacity and high swelling and shrinkage characteristics. Due to its peculiar characteristics, it forms a very poor foundation material for road construction. Soaked laboratory CBR values of Black Cotton soils are generally found in the range of 2 to 4%. Due to very low CBR values of Black cotton soil (BC soil), excessive pavement thickness is required for designing for flexible pavement.

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Chapter 3 OBJECTIVE OF THE PROJECT

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OBJECTIVES OF THE PROJECT As stated above, road construction in black cotton soil area is difficult and hence there is need of increasing the strength of black cotton soil as a subgrade for road. Thus, the soil properties can be improved by soil stabilization techniques. Thus, the problem statement of the project is to stabilize the subgrade soil(black cotton soil) using a suitable stabilizer. Chemical stabilizers like cement, lime are added to soil to improve soil strength, stress-strain behavior, and durability etc. Thus, objectives of the project are as follows 1. To study the properties of black cotton soil available locally. 2. To check the suitability of fly ash-lime combined mixture as a stabilizer for the black cotton soil in Maharashtra 3. To obtain the correct proportion of soil, fly ash and lime to be mixed for stabilization.

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Chapter 4 METHODOLOGY

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METHODOLOGY 4.1 Properties of black cotton soil Locally available fine grained black cotton soil from nearby site was acquired and fly ash from Nashik thermal power station was procured. The necessary experiments to be carried out on BC soil are sieve analysis, Standard proctor test, Atterberg‟s limits test, Differential swell test and unconfined compressive test. The procedures for tests were according to IS codes, which are described below. 4.1.1 Sieve analysis: The portion of the soil sample retained on 4.75-mm IS Sieve, selected for test, was weighed and the mass recorded As the mass of the sample uncorrected for hygroscopic moisture. The quantity of the soil sample taken shall depend on the maximum particle size contained in the soil. The sample was separated into various fractions by sieving through the Indian Standard Sieves, 100mm, 75mm,19mm & 4.75mm. While sieving through each sieve, the sieve was agitated so that the sample rolls in irregular motion over the Sieve. Any particles may be tested to see if they will fall through but they shall not be pushed through. The material from the sieve may be rubbed, if necessary, with the rubber pestle in the mortar taking care to see that individual soil particles are not broken and resieved to take sure that only individual particles are retained. The quantity taken each time for sieving on each sieve was such that the maximum weight of material retained on each sieve at the completion of sieving should be noted. 4.1.2 Hydrometer analysis: We took the fine soil from the bottom pan of the sieve set, place it into a beaker, and add 125 mL of the dispersing agent (sodium hexametaphosphate (40 g/L)) solution. Stirred the mixture until the soil is thoroughly wet. Let the soil soak for at least ten minutes. While the soil is soaking, add 125mL of dispersing agent into the control cylinder and it was filled with distilled water to the mark. Take threading at the top of the meniscus formed by the hydrometer stem and the control solution. A reading less than zero is recorded as a negative

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(-) correction and a reading between zero and sixty is recorded as a positive (+) correction. This reading is called the zero correction. The meniscus correction is the difference between the top of the meniscus and the level of the solution in the control jar (Usually about +1). Shake the control cylinder in such a way that the contents are mixed thoroughly. Insert the hydrometer and thermometer into the control cylinder and note the zero correction and temperature respectively. Transferred the soil slurry into a mixer by adding more distilled water, if necessary, until mixing cup is at least half full. Then mix the solution for a period of two minutes. Immediately transfer the soil slurry into the empty sedimentation cylinder. Add distilled water up to the mark. Cover the open end of the cylinder with a stopper and secure it with the palm of your hand. Then turn the cylinder upside down and back upright for a period of one minute. (The cylinder should be inverted approximately 30 times during the minute.) Set the cylinder down and record the time. Remove the stopper from the cylinder. After an elapsed time of one minute and forty seconds, very slowly and carefully insert the hydrometer for the first reading.(Note: It should take about ten seconds to insert or remove the hydrometer to minimize any disturbance, and the release of the hydrometer should be made as close to the reading depth as possible to avoid excessive bobbing). The reading is taken by observing the top of the meniscus formed by the suspension and the hydrometer stem. The hydrometer is removed slowly and placed back into the control cylinder. Very gently spin it in control cylinder to remove any particles that may have adhered. Take hydrometer readings after elapsed time of 2 and 5, 8, 15, 30, 60 Minutes and 24 hours.

4.1.3 Standard proctor test: A 3-kg sample of air dried soil passing the 20 mm IS test sieve shall be taken. The sample shall be mixed thoroughly with a suitable amount of water depending on the soil type. The mould, with base plate attached, shall be weighed to the nearest 1 g (ml). The mould shall be placed on a solid base, such as a concrete floor or plinth and the moist soil shall be compacted into the mould, with the extension attached, in three layers of approximately equal mass, each layer being given 25 blows from the 2*6-kg rammer dropped from a height of 310 mm above the soil. The blows shall be distributed GEC BHARATPUR

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uniformly over the surface of each layer. The operator shall ensure that the tube of the rammer is kept clear of soil so that the rammer always falls freely. The amount of soil used shall be sufficient to fill the mould, leaving not more than about 6 mm to be struck off when the extension is removed. The extension shall be removed and the compacted soil shall be leveled off carefully to the top of the mould by means of the straightedge. The mould and soil shall then be weighed. The compacted soil specimen shall be removed from the mould and placed on the mixing tray. The water content of a representative 3mm of the specimen shall be determined as in IS: 2720 (Part 11 ). The remainder of the soil specimen shall be broken up, rubbed through the 20-mm IS test sieve, and then mixed with the remainder of the original sample. Suitable increments of water shall be added successively and mixed into the sample, and the above procedure shall be repeated for each increment of water added. The total number of determinations made shall he at least five, and the range of moisture contents should be such that the optimum moisture content, at which the maximum dry density occurs, is within that range. 4.1.4 Liquid limit test:

About 120 g of the soil sample passing 425-micron IS Sieve shall be mixed thoroughly with distilled water in the evaporating dish or on the flat glass plate to form a uniform paste. The paste shall have a consistency that will require 30 to 35 drops of the cup to cause the required closure of the standard groove. In the case of clayey soils, the soil paste shall be left to stand for a sufficient time (24 hours) so as to ensure uniform distribution of moisture throughout the soil mass. The soil should then be re-mixed thoroughly before the test. A portion of the paste shall be placed in the cup above the spot where the cup rests on the base, squeezed down and spread into position, with as few strokes of the spatula as possible and at the same time trimmed to a depth of one centimeter at the point of maximum thickness, returning the excess soil to the dish. The soil in the cup shall be decided by firm strokes of the grooving tool along the diameter through the centre line of the cam follower so that a clean, sharp groove of the proper dimensions is formed. The cup shall be fitted and dropped by turning the crank at the rate of two revolutions per second until the two halves of the soil cake come in contact with bottom of the groove GEC BHARATPUR

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along a distance of about 12 mm. This length shall be measured with the end of the grooving tool or a ruler. The number of drops required to cause the groove close for the length of 12 mm shall be recorded. A little extra of the soil mixture shall be added to the cup and mixed with the soil in the cup. The pat shall be made in the cup and the test repeated. In no case shall dried soil be added to the thoroughly mixed soil that is being tested. The procedure shall be repeated until two consecutive runs give the same under of drops for closure of the groove. A representative slice of soil approximately the width of the spatula, extending from about edge to edge of the soil cake at right angle to the groove and including that portion of the groove in which the soil flowed together, shall be taken in a suitable container and its moisture content expressed as a percentage of the oven dry weight otherwise determined as described in IS : 2720 ( Part 2 )-1973*. The remaining soil in the cup shall be transferred to the evaporating dish and the cup and the grooving tool cleaned thoroughly. The operations shall be repeated for at least three more additional trails (minimum of four in all), which the soil collected in the evaporating dish or flat glass plate, to with sufficient water has been added to bring the soil to a more fluid condition. In each case the number of blows shall be recorded and the moisture content determined as before. The specimens shall be of such consistency that the number of drops required to ~close the groove shall be not less than 15 or more than 35 and the points on the flow curve are evenly distributed in this range. The test should proceed from the drier (more drops) to the wetter ( less drops ) condition of the soil. The test may also be conducted from the wetter to the drier condition provided drying is achieved by kneading the wet soil and not by adding dry soil. „A flow curve‟ shall be plotted on a semi-logarithmic graph representing water content on the arithmetical scale and the number of drops on the logarithmic scale. The flow curve is a straight line drawn as nearly as possible through the four or more plotted points. The moisture content corresponding to 25 drops as read from the curve shall be rounded off to the nearest whole number and reported as the liquid limit of the soil.

4.1.5 Plastic limit test: The soil sample shall be mixed thoroughly with distilled water in an evaporating dish or on the flat glass plate till the soil mass becomes plastic enough to be easily molded with fingers. In the case of clayey soils the plastic soil mass shall be left to stand for a GEC BHARATPUR

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sufficient time (24 hours) to ensure uniform distribution of moisture throughout the soil. A ball shall be formed with about 8 g of this plastic soil mass and rolled between the fingers and the glass plate with just sufficient pressure to roll the mass into a thread of uniform diameter throughout its length. The rate of rolling shall be between 80 and 90 strokes/min counting a stroke as one complete motion of the hand forward and back to the starting position again. The rolling shall be done till the threads are of 3 mm diameter. The soil shall then be kneaded together to a uniform mass and rolled again. This process of alternate rolling and kneading shall be continued until the thread crumbles under the pressure required for rolling and the soil can no longer be rolled into a thread. The crumbling may occur when the thread has a diameter greater than 3 mm. This shall be considered a satisfactory end point, provided the soil has been rolled into a thread 3 mm in diameter immediately before. At no time shall an attempt be made to produce failure at exactly 3 mm diameter by allowing the thread to reach 3 mm, then reducing the rate of rolling or pressure or both, and continuing the rolling without further deformation until the thread falls apart. The pieces of crumbled soil thread shall be collected in an air-tight container and the moisture content determined as described in IS: 2720 (Part 2)-1973;

4.1.6 Shrinkage limit test: Keep the specimen in suitable small dill and air-dry it. Then dry the specimen in the dish to constant weight in an oven at 105 to 110°C. Remove the specimen from the oven and smoothen the edges by sand papering. Brush off the soil dust from the specimen by a soft paint brush. Place the specimen again in the cleaned dish and dry it in an oven to constant weight. Cool the oven-dry specimen in a desiccators and weigh it with the dish. Determine the oven-dry weight of the specimen.

4.1.7 Differential swell index: Two 10 gm soil specimens of oven dry soil passing through 425-micron IS Sieve was taken. Each soil specimen was poured in each of the two glass graduated cylinders of 100 ml capacity. One cylinder was then be filled with kerosene oil and the other with distilled writer up to the 100 ml mark. After removal of entrapped air (by gentle shaking or stirring with a: tglass rod), the soils in both the cylinders was allowed to settle. Sufficient time was allowed for the soil sample to attain equilibrium state of volume without any further GEC BHARATPUR

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change in the volume of the soils. The final volume of soils in each of the cylinders was read out. The level of the soil in the kerosene graduated cylinder was read as the original volume of the soil samples, kerosene being a non-polar liquid does not cause swelling of the soil. The level of the soil in the distilled water cylinder was read as the free swell level. The differential swell index of the soil is calculated as follows:

Differential swell in, percent

Where, V d= the volume of soil specimen read from the graduated cylinder containing distilled water, Vk = the volume of soil specimen read from the graduated cylinder containing kerosene

4.2 Preparation of samples Samples were prepared using a mould of circular cross-section of 36 mm diameter and height 75 mm. The samples were casted at with their respective optimum moisture content calculated by standard proctor test for every proportion. After the specimen was formed, the ends were trimmed perpendicular to the long axis and removed from the mould. Representative sample cuttings were obtained for the determination of unconfined compressive strength test. The 9 proportions were casted as given in table below. 2 samples for each proportion were made.

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Lime in %

Fly ash in %

Soil in %

4

10

100

4

20

100

4

30

100

4

40

100

4

50

100

4

60

100

6

10

100

6

20

100

6

30

100

6

40

100

6

50

100

6

60

100

8

10

100

8

20

100

8

30

100

8

40

100

8

50

100

8

60

100

10

10

100

10

20

100

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10

30

100

10

40

100

10

50

100

10

60

100

12

10

100

12

20

100

12

30

100

12

40

100

12

50

100

12

60

100

14

10

100

14

20

100

14

30

100

14

40

100

14

50

100

14

60

100

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4.3 Curing of samples Samples were cured for 7, 14 and 21 days. Samples were kept in plastic bags and covered by wet gunny bags to retain the original moisture content. 4.4 Unconfined compressive strength test: Unconfined compressive strength test on samples was done. The procedure for test is as below: The initial length, diameter and weight of the specimen shall be measured and the specimen placed on the bottom plate of the loading device. The upper plate shall be adjusted to make contact with the specimen. The deformation dial gauge shall be adjusted to a suitable reading, preferably in multiples of 100. Force shall be applied so as to produce axial strain at a rate of 0.5 to 2 percent per minute causing failure with 5 to 10. The force reading shall be taken at suitable intervals of the deformation dial reading. Compressive stress, shall be determined from the relationship: P/A NOTE - Up to 6% axial strain force, readings may be taken at an interval of 0.5 mm of the deformation dial reading. After 6% axial strain, the interval may be increased to 1.0 mm and, beyond 12% axial strain it may be increased even further. The specimen shall be compressed until failure surfaces have definitely developed, or stress-strain curve is well past its peak, or until axial strain of 20 percent is reached. The failure pattern shall be sketched carefully and shown on the data sheet or on the sheet presenting the stress-strain plot.

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Chapter 5 RESULTS AND DISCUSSIONS

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5.1 Preliminary observations and readings 5.1.1 Properties of black cotton soil The engineering properties of soil are investigated as follows: Liquid limit: 60.33% Plastic limit: 21.5% Plasticity index: 38.83% Shrinkage limit: 13.66% Differential swell: 70% Optimum moisture content:26.4% Maximum dry density: 1.33 gm/cc Unconfined compressive strength: 30KN 5.1.2 Unconfined compressive strength tests results of different proportions sr.no.

proportion

7 day strength

1

4:10:100

63.26674

80.75306

79.10641

2

4:20:100

72.43254

45.99188

56.36429

3

4:30:100

67.97688

51.76302

104.6748

4

6:10:100

64.94172

127.2587

134.8742

5

6:20:100

91.38305

104.0796

104.0796

6

6:30:100

74.17492

81.52757

142.4454

7

8:10:100

99.61802

24.2101

123.7935

8

8:20:100

154.3113

123.8668

115.0261

9

8:30:100

88.99083

75.49722

191.4123

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5.1.3 Effect on strength when fly ash is varied keeping lime constant

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5.1.4 Effect on strength when lime is varied keeping fly ash constant

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5.1.5 Effect of curing time on the strength of the sub grade

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5.1.6 Discussions about the preliminary reading 

The graphs of different combinations with different curing times have been drawn and analyzed keeping two parameters constant.



The 5.1.3 graphs show variation in strength with variation with fly ash keeping lime constant. From the graph, we come to know that the graphs are increasing with the increase in fly ash. Thus, 30 % fly ash gives us the maximum strength. However, we cannot understand whether the 30% is optimum proportion or not. Hence we need to take tests with increasing the percentage of fly ash.



The 5.1.3 graphs show variation in strength with variation with lime keeping fly ash constant. From the graph, we come to know that the graphs are increasing with the increase in lime. Thus, 8 % lime gives us the maximum strength. However, we cannot understand whether the 8% is optimum proportion or not. Hence we need to take tests with increasing the percentage of lime.



The 5.1.3 graphs show variation in strength with variation with curing time. From the graph, we observe that the better and reliable readings can be observed at the curing time of 21 days. Hence, the final readings are taken for the curing time of 21 days.

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5.2 Final Observation and readings Table 1 : unconfined compressive strength of black cotton soil taken after 21 day curing Sr .no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

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lime 4 4 4 4 4 4 6 6 6 6 6 6 8 8 8 8 8 8 10 10 10 10 10 10 12 12 12 12 12 12 14 14 14 14 14 14

fly ash 10 20 30 40 50 60 10 20 30 40 50 60 10 20 30 40 50 60 10 20 30 40 50 60 10 20 30 40 50 60 10 20 30 40 50 60

21 day compressive strength 79.10 56.36 104.67 43.4 22.28 21.06 134.87 104.07 142.44 38.3 15.24 21.08 123.79 115.02 191.41 62.90 38.75 64.19 100 105 112.51 111.06 100 50.34 140.4 160.3 195.66 190.2 117.4 100.56 120.7 140.64 180.24 179.19 115.57 70.8

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5.2.1 Variation in compressive strength with variation in fly ash (explained using bar chart)

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5.2.2 Variation in compressive strength with variation in lime (explained using bar chart)

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5.2.3 Variation in compressive strength with variation in fly ash (explained using line graphs)

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5.2.4 Variation in compressive strength with variation in lime (explained using line graphs)

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Discussions about the final readings obtained: 

The final observation and readings have been analysed using bar charts and line graphs.



From the graphs, we come to know that the strength of BC soil increases with increase in lime content and then decreases with increase in lime. Thus, the strength V/S lime percentage increases first and then drops down showing us the optimum proportion of lime as 8%.



From the graphs, we come to know that the strength of BC soil increases with increase in fly ash content and then decreases with increase in fly ash. Thus, the strength V/S lime percentage increases first and then drops down showing us the optimum proportion of lime as 8%.



Thus, we come to know that the optimum proportion for black cotton soil of sangli is 12% lime and 30% fly ash.

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Properties of black cotton soil with12% lime and 30% fly ash Liquid limit: 42% Plastic limit: 27.14% Plasticity index: 14.86% Shrinkage limit: 19.01% Clay: 9 % Differential swell: 25% Optimum moisture content: 30% Maximum dry density: 1.3 gm/cc Unconfined compressive strength: 195 KN

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Comparison between black cotton soil with no stabilizer and black cotton soil added with 12% lime and 30% fly ash

Index properties

Black cotton soil with no stabilizer

Black cotton soil with 12 %

remarks

Liquid limit

60.33 %

42.00

Liquid limit has decreased

Plastic limit

21.50

27.14

Plastic limit has increased

Plasticity index

38.83

14.86

Plasticity index has reduced

Shrinkage limit

13.66

19.01

Shrinkage limit has increased

Differential swell

70%

25%

Swelling has decresed considerably

Optimum moisture content

26.4%

30%

OMC has increased

Maximum dry density

1.33 gm/cc

1.3 gm/cc

MDD has decreased little.

195 KN

Strength has increased considerably

Unconfined compressive strength



30 KN

Desired properties of soil have been achieved. Hence, stabilization method and proportion of lime, fly ash and soil is correct.

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Chapter 6 Application formula

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6.1 Explanation of the derivation of formula Lime is used for increasing the strength of sub grade soil whereas fly ash is used to bring economy in the process. From our research, we come to know that the strength achieved per percentage of lime is 25 KN and the strength achieved per percentage of fly ash is 3 KN. Thus, the one percent of lime is equivalent to 8.33 percent of fly ash. Thus, the use of lime can be reduced by replacing the lime with equivalent percentage of fly ash thereby maintaining the same strength. However, Through our research, we come to know that the optimum percentage of fly ash is 30 percent and maximum fly ash that can be used is 35 %. Thus, we limit the value of QF in equation below to 35 %.

6.2 Step wise procedure for calculating the percentage of lime and fly ash required for stabilization of any black cotton Step 1 – find out the Ph of the black cotton soil Step 2 – Use ASTM D 6276 to calculate the minimum lime required for stabilization of BC soil Step 3 – Use the following formula to calculate the percentage of lime to be added and percentage of fly ash to be added

QL = Q0

-

(C – M ) (C/Q0 )

QF

=

(Q – Q0 ) * 8.33

Where, QL = percentage of lime that will be used Q0 = percentage of lime required as per ASTM D 6276 QF = percentage of fly ash required to replace lime C = cost of using Q0 percentage of lime M = available money or budget of stabilization GEC BHARATPUR

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Chapter 7 CONCLUSION & SCOPE

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7.1 Conclusion 

Lime and fly ash are effective and efficient stabilizer. The strength of black cotton soil can be increased by using fly ash and lime combination.



Through our research, we have come to know the optimum proportion of lime and fly ash for the locally available BC soil in Sangli. The optimum proportion is 12% lime and 30% fly ash.



Through the differential swell reading, we come to know that for the optimum proportion the swelling is considerably reduced. Thus, fly ash and lime can effective in both increasing strength as well as reducing swelling of BC soil.

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7.2 Future scope of the project 

In the project, we have calculated the optimum proportion of lime and fly ash for black cotton soil available in sangli district. However, there is need to generalize the use of lime + fly ash combination on black cotton soils. The use of fly ash and lime can be generalized for all black cotton soils if the clay percentage for different lime + fly ash combinations can be found out. By knowing the effect of different combinations on clay percentage of soil, we can find out the optimum proportion for any black cotton soil with particular clay percentage.

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Chapter 8 REFERENCES

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8.1 books  

Behaviour of saturated expansive soil and control methods vol 1. - Prof. Katti Soil Mechanics and Foundation engineering – Dr. K.S.Arora

8.2 Technical research papers 

Baban ram and Sunil kumar chaudhary, “ Cost effective and eco friendly construction of rural roads- need of hour”, Indian highways, Nov 2010



S. Bhuvaneshwari , S. G. Robinson , S. R. Gandhi . “Stabilization of expansive soils using fly ash”, fly ash utilization program, TIFAC, DST, new Delhi



Erdal Cocka (2001) “ Use of class c fly ashes for the stabilization of an expansive soil”, Journal of geotechnical and geoenvironmental engineering, vol. 127, July, pp. 568-573



Pandian, n.s.,krishna, k.c. leelavathamma b., (2002), effect of fly ash on the cbr behavior of Soils , Indian geotechnical conference , Allahabad , vol.1,pp.183-186.



Phanikumar b.r., & radhey s.sharma(2004) “effect of fly ash on engg properties of expansive Soil” journal of geotechnical and geoenvironmental engineering vol. 130, no 7,july, pp. 764-767.



O.o. amu, a.b. fajobi and b.o. oke. “effect of eggshell powder on the stabilizing potential of lime on an expansive clay soil”. Research journal of agriculture and biological sciences 1(1): 80-84, 2005 © 2005, insinet publication



Niroj MIshra, Sudhira Rath, Siddharth Sankar biswat, Girija Sankar Pujhari,” Use of fly ash and other stabilizing agents for construction of cost effective roads in sambhalpur district in Orissa, Indian Highways, July 2010.



A. Shrirama rao and G. Shridevi , “ Improving the performance of expansive soil subgrades with lime – stabilized fly ash cushion, Indian highways , oct 2010



A.N. Ramakrishna and A.V. Pradeepkumar, “Effect of moisture content on strength behavior of BC soil- Rice husk ash- lime mixes, Indian Highways, jan 2008.



N. K. Ameta, d.g. m. Purohit, a. S. Wayal .”Characteristics, problems and remedies of expansive soils of rajasthan”, india.

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Udayashankar d. Hakari s. C. Puranik “evaluation of swell potential and identification of expansive and problematic soils in civil engineering works by newly developed matrices Based on index and grain size properties”



Hesham ahmed hussin ismaiel “treatment and improvement of the geotechnical properties of different soft fine-grained soils using chemical stabilization”

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