Black cotton soil is a typical expansive soil having the property of shrinkaging and swelling on variation of its moisture content. For all types of structures, the foundation is the most vital or important part and it must be strong enough to support the whole structure. For the foundation to be strong, the soil around it has to be capable of safely dissipating the load. Speaking with respect to soils, we need to gather technical information about their properties and characteristics which may influence their behavior. Expansive type of soils usually face more problems with heavily loaded structures as compared to light structures.
In this paper, the exploratory outcomes acquired in the laboratory on expansive soil treated with lime and along these lines by coir are introduced. Our investigation was done to check the enhancements in the quality of expansive soil with differing rates of lime and in this way of coir. The test outcomes, for example, compaction test, California bearing ratio(CBR),unconfined compressive test(UCS) were obtained on black cotton soil at first, then with addition of lime at various contents – 0%,2%,4%,6%, after which coir was varied at 0%,0.25%,0.5%,0.75%,1% keeping optimum lime content at constant value.
Tests results have indicated that the addition of lime and coir in the soil sample have shown an increment in the strength parameters of black cotton soil. CBR value increased from 3.02% to 7.5% for black cotton soil mixed with 4% of lime content by weight and further increased more to 12.03% with an addition 0.5% coir by weight of the soil. Similarly, UCS value rose from 54.9 kPa to 127 kPa with the addition of 4% lime content by weight of soil and further increased to 195 kPa on addition of 0.5% of coir by weight of soil. In conclusion, it could be said that optimum lime and coir content for the stabilization of black cotton soil of North Karnataka region is 4% and 0.5% respectively.
CHAPTER – 1
Black cotton soil has wide development in Mumbai, the western part of Madhya Pradesh, northern parts of Karnataka, parts of Gujarat, and in some parts of Madras. In Mumbai, a large area is occupied by soils derived from the Deccan trap. Black Cotton soils retain water vigorously, swell, turn out to be delicate abd lose quality . These soils are effortlessly compressible when wet and have a propensity to hurl amid wet conditions. Black cotton soils contract in volume and create cracks in mid-summer. They are described by extraordinary hardness and breaks when dry. These properties make them poor foundation soils and earth development material. The steadiness and execution of the asphalts are significantly impacted by the sub level and dike as they fill in as establishments for asphalts.
For working up a better than average and strong road in black cotton soil districts, the nature of the soils should be truly understood and should be offset with a particular ultimate objective to upgrade their outlining properties. On such soils fitting advancement practices and refined procedures for arrangement ought to be grasped.
Efforts are in this way been made to reinforce the soil sample by stabilization of soil by cement, lime, fly ash or geo-synthetic to enhance its performance. However, the procedure which has been utilized in our project is an adjustment of lime and soil stabilization by coir strands or fibers. Lime adjustment helps in enhancing the strength, durability and furthermore limits the dampness varieties in the soil. Lime should be compact for acquiring adequate strength and durability by keeping up OMC and a similar supposition is made in the trial assurance of the required lime extent. Nature of lime to be included relies on the particular surface zone of the soil particles and it is more for fine-grained soils even up to 15% by weight of soil. The stabilization of black cotton soil with lime has been done in three different proportions of lime i.e. 0%, 2%, 4%, and 6%.
Soil reinforcement is a powerful and dependable method for enhancing quality and dependability of soil. In our project, we have utilized coir fibers for the purpose of soil reinforcement. Coir or coconut filaments have a place with the gathering of hard auxiliary strands. It is a commercial product acquired from the husk of the coconut. The coir fiber is elastic enough to curve without breaking and it holds a curl just as forever waved. Shorter sleeping pad filaments are isolated from the long swarm strands which are thus a waste in the coir fiber industry. So this coir fiber waste can be used in the stabilization of soil and consequently it can be successfully disposed off.
BLACK COTTON SOIL
Black cotton soil also is known as swell-shrink soil possess the property of swelling and shrinking to a very large extent when the moisture content is varied. This variation leads to significant distress in the soil which is detrimental to the structures that are overlying the soil. During rainy season enough moisture is available for the soil to combine with water and the soil becomes very soft. As a result, the moisture holding capacity of the soil becomes negligible. On the contrary during the dry seasons (summer), evaporation leads to a loss in the water that is being held in the soil and the soil hardens. These soils are mainly found in the arid and the semi-arid regions of the world and pose a great threat to the structures that are built upon them if they are not effectively treated. Soils that constitute montmorillonite as a clay minerologyto a considerable extent are generally expected to exhibit the above-mentioned properties. The damages caused by these soils to structures all over the world have roughly accounted for a loss of billions of dollars.
The black cotton soil in the subcontinent is mostly found in Karnataka, Maharashtra, Madhya Pradesh, Andhra Pradesh and Gujarat. In the states of Karnataka, the black cotton soil is mostly found in Chitradurga, Bijapur, Gulbarga, Dharwar, Raichur, Bidar and Bellary districts. These soils have also been found in the river valleys of Narmada, Godavari, Krishna, and Tapi. Rocks such as basalt undergo chemical decomposition by the action of decomposing agents and residual soils are left behind at these places. Cooling of lava and weathering of other rocks are the other formation processes of these kinds of soils. These soils are found to be rich in magnesia, iron lime and alumina and lack phosphorus, nitrogen and organic content.
The different soils available in India are shown in Fig. 1.1.
Fig. 1.1 Map of India showing different types of soil
The dark cotton soil is characterized by two primary classes in view of the dirt and sediment extent:
Trappean dark clayey soil: It is found in the real parts of Peninsular India and is overwhelming because of the better constituents (65%-80%).
Trappean dark loamy soil: It is for the most part found in the Wainganga valley and the northern Konkan drift with a sediment substance of 30%-40%.
In our experimental study we have used quick lime for the stabilization purpose, although other forms of lime such as quick lime and hydrated lime can be utilized for the same purpose. Quick lime is obtained from limestone i.e. calcium carbonate by converting into calcium oxide. Hydrated lime is obtained when quick lime reacts with water however it is hydrated lime that converts entire soil structure to cementitious matrix. High calcium with not more than 5% magnesium oxide or hydroxide is often used for stabilisation .In certain situations dolomitic lime is used which extends 35 to 46% mgo or hydroxide. Dolomitic lime has found to be working well in soil stabilization in spite of its magnesium part reacting more slowly than the calcium part. A variety of soil types are treated using either only lime or its min will different other materials.
The extent of reaction between the clay particles and lime as well as the development of ultimate strength in the stabilized layer is decided by the mineralogical structure and properties of soil. As a rule fine grained soils (with at least 25% going through 74mm sieve and a plastic limit more than 10 are thought to be great potential for stabilisation . soil having critical measures of natural organic material (more prominent than around 1%) or sulphates (more prominent than 0.3%) may require extra lime.
Fine grained soils that is used as subgrade or soil base can be permanently stabilised in order to make it structurally sound for pavement. In case of reconstruction and development of new as well as worn out roads. Stabilization of base coarse is done by adding 2 to 4% lime by weight of the dry soil. Lime is additionally utilised to enhance the properties of soil subgrade.
1.21. The chemistry behind lime treatment.
Immediate chemical reactions start to happen as soon as lime and water is mixed with a clay soil.
Drying: on chemically combining with water quick lime instantaneously hydrates and heat is released, water present in the voids get dried because of its participation in this reaction and the heat generated evaporates any additional moisture. The clay particles further reacts with the hydrated lime so produced. Moisture holding capacity will get reduced because of the additional drying due to these subsequent reactions.
Modification: water and the other ions which are present on the surface of clay particles gets displaced by the migration of calcium ion from hydrated lime after initial mixing. The soil winds up granular and friable, which makes it easier to compact and work .At this particular point the plastic limit of the soil declines significantly as does its inclination to swell and shrink. The procedure which is called flocculation and agglomeration for the most part happens in a matter of hours.
Stabilisation: clay particles tend to breakdown on the account of increased due to addition of lime and water to soil. Calcium present in lime reacts with the released silica and alumina forming calcium silicate hydrates and calcium aluminate hydrates .CSH and CAH re cementitious products forms the matrix contributing to the strength of lime stabilized layer.
1.2.2. Advantages and disadvantages of different forms of lime application.
Various factors have to be considered and thought before selecting a particular technique for lime stabilization in a project work. These factors include:
Location of project – rural or urban
Availability of adequate nearby water resource
Some of the pros and cons of different lime application techniques are as follows:
Dry Hydrated Lime
Advantages: Application of dry hydrated lime takes much less time compared to that of slurry. It can be used for clay drying but quick lime is found to be more effective than dry hydrated lime.
Disadvantages: It consists of very fine particles which can lead to dust problems when applied, hence cannot be used around populated areas.
Dry Quick Lime
Advantages: The concentration of lime is more in quick lime as compared to hydrated lime. It contains 20 -24 % extra available lime oxide content. Hence, in conditions where quicklime gets fully hydrated, the about 4% hydrated lime is equal to 3% of quick lime. Smaller storage facilities is required because of its greater bulk density. The exothermic reactions between water and quick lime warms the soil which in turn helps in extending the construction season. There is no issue of dust generation as large particles are present.
Disadvantages: 32% by weight of water is required by quicklime to get hydrated and then also leads to significant additional evaporation loss due to exothermic nature of reaction. Proper conditions such as adequate water addition, mellowing and mixing should be ensured during the usage of quick lime. These conditions especially adequate water requirement may challenge the usage of quick lime in remote areas where there is no nearby water source. More mixing is required by quick lime compared to other forms of lime as the large particles of quick lime frost hydrates and then afterwards gets mixed with soil.
Advantages: There is no dust problems and it can be easily distributed all over the project area evenly. Sprinkling and spreading can be carried out simultaneously and requirement of additional water for final mixing is less.
Disadvantage: Rate of application is much more slower compared to other forms of lime. Additional equipment are required which in turn increases the total expense of construction work. It is suitable for drying applications.
Extra precautions need to be taken while handling hydrated lime and quick lime, as hydrated lime can cause irritation to eyes and skin whereas quicklime causes burns. While handling, spreading and mixing workers should use tight fitting goggles, long sleeves, pants tucked into boots, gauntlet gloves. If lime gets in contact with skin, then wash it off and if there is an occurrence of contact with eyes flush out with clean water quickly and see a specialist. Protective creams should be used with sensitive skin. Proper safety measures such as nose mask should also be used in order to prevent inhalation.
In spite of its poor properties soil has been widely used as construction material by the civil engineers because it is readily available and least expensive material. Invative ideas have constantly put forward by the resraech workers so has to improve mechanical properties. In order to ensure sustainable development of the society waste materials such as coal ash, plastics, geosynthetic materials ,stone quarry, polythene bags etc should be used in the construction process which in turn help to save the natural resources for future generation. In our experimental study we have used coir fiber as waste material. Coir is a commercial product extracted from coconut husk and it belongs to a group of hard structural fibers.
The coir fiber can be twisted without breaking because of its elasticity and it can bear curl as permanenetly waved. As coir fiber is a waste product of factories, making use of it for soil stabilization is economical and it is also environmental friendly as it is bio degradable. The addition of coir to soil can help in consolidation of soil and hence make it more stable. Usually, the length of the coir does not change its effect on the soil however, the contents of the coir may affect the soil significantly. Thus, more study and research are being done on this topic to understand the properties of coir fibre. Coir fibre is being used more and more across different countries as it has proven to improve overall engineering properties.
The soil-fiber mixture is effective in all types of soil (i.e., sand, silt and clay). Local availabilityand low cost adds to the advantage of coir material. Its biodegradability doesn’t possess any threat to the environment. Our experimental study projects the influence of effectiveness of coir fiber on the CBR and UCS value of black cotton soil of Davangere, Karnataka, India. UCS test as well as soaked and unsoaked CBR values have to be conducted on the soil-coir mixture with varying percentages of coir ranging from 0.25,0.5,0.75 and 1%. These values will be compared to that of unmixed soil. Introduction of synthetic fiber have put a decline in the use of coir fiber for mats, brooms, brushese and hence, use of coir fiber in the construction sector woild help to minimize adverse ecological effects.
The focal point of this project is to stabilize the black cotton soil utilizing lime and coir fiber. The project deals with discovering and finding out the optimum lime and coir content. In this project, we aimed for determining the California bearing ratio, unconfined compressive strength, optimum moisture content and maximum dry density of the mixture of soil and lime with different coir fiber contents. We will likewise analyze the influence of percentages of lime and coir fiber on the California bearing ratio, unconfined compressive strength, optimum moisture content and maximum dry density.
In spite of the fact that BCS is exceptionally fertile soils, it isn’t great as a road or foundation construction. Black cotton soils are highly expansive and experience high shrinkage and swelling of fluctuating moisture content. Because of swelling and shrinking process, it brings about surface cracks in amid dry seasons. Cracks vanish in wet season yet an uneven soil surface remains because of sporadic swelling and shrinking. The black cotton soils have low strength and are subjected to excessive volume changes, making their utilization for construction purposes exceptionally troublesome. Instability of these soils makes more harm to structures than some other natural dangers, including earthquakes and floods, unless legitimate soil stabilization performed. Hence lime and coir are utilized for stabilization purposes which bring about increment of bearing and shearing strength of soil.
To carry out the characteristics tests of Black cotton soil.
To observe the influence of the Lime and coir on the compaction characteristics of the black cotton soil.
To determine the unconfined compressive strength and CBR of a mixture of soil with different lime and coir contents.
To examine the influence of percentage of Lime on the unconfined compressive strength and CBR values of soil mixture.
To study the effect of percentage of coir used on the unconfined compressive strength and CBR values of the soil-lime mixture.
OVERVIEW OF THE REPORT
This report incorporates various numbers of chapters. For the convenience of the reader a consolidated overview is mentioned below:
CHAPTER 1: INTRODUCTION
This chapter provides an insight into the project and its various aspects along with the motivation behind opting this as our study and the objectives of this project as well as literature review done for journals related to the study.
CHAPTER 2: EXPERIMENTS CONDUCTED
This chapter includes a brief discussion of the experiments conducted along with the purpose and principle behind it. It also includes the procedures and precautions to be taken while conducting the experiments.
CHAPTER 3: MATERIALS AND METHODOLOGY
In this chapter, the characterization of the materials is discussed along with the experiments which were carried out for the same. The methodology of the characterization and experiments conducted were also discussed.
CHAPTER 4: RESULTS AND DISCUSSION
This chapter includes the results of various tests conducted in this project and the discussion of these results is done.
CHAPTER 5: CONCLUSION
After obtaining the results from the various tests and analyzing them, numerous conclusions were drawn. These conclusions are mentioned in this chapter.
CHAPTER 6: REFERENCES
This includes the citation for the various journals and technical papers reviwed and refered to for the experimental study.
The characteristics of the soil are examined in order to determine the soil properties for use in field conditions. Tests like specific gravity, grain size distribution, atterberg’s limits test, Hydrometer Analysis, Compaction Test, UCS Test and CBR Test were conducted in accordance with IS 2720.
2.1. SPECIFIC GRAVITY
The specific gravity of soil represents the nature of the soil. Soils which contains organic matter and porous materials have a specific gravity less than 2. On the other hand, the soils with heavy constituents have a specific gravity greater than 3. These values help in determining the degree of saturation and void ratio.
Fig. 2.1 Pycnometer
The specific gravity of a black cotton soil can be determined either by density bottle or pycnometer as per the IS 2720 (Part 3/ Sec 1) 1980. The pycnometer is shown in Fig. 2.1. It is expressed as the ratio of the mass of soil to the mass of the equal volume of water at the same temperature.
406082529971900 Specific Gravity = (M2?M1)
Where, M1 = Mass of pycnometer or density bottle
M2 = Mass of pycnometer or density bottle and soil
M3 = Mass of pycnometer or density bottle and soil and water M4 = Mass of pycnometer or density bottle and water
Fig. 2.2. Sieve shaker
Mechanical sieve analysis was conducted on the expansive soil in order to determine the particle size distribution in accordance with IS 2720 (Part 4). Fig. 2.2 shows the sieve shaker apparatus. The soil passing through 4.75mm IS sieve was oven dried at a temperature of 105oC to 110oC.and with the help of quartering method, the required amount of soil is taken. Approximately 500g of soil was sprayed with water and left for 24 hours for complete saturation. The soil was then thoroughly washed through a 75-micron sieve and the retained portion was air dried. The set of sieves were arranged in a decreasing order and the dry soil was placed in the topmost sieve of 4.75mm. This arrangement was then rested on a mechanical shaker and was shaken for around ten minutes. The mass of soil retained on each sieve was noted for determining particle distribution.
Fig. 2.3 Casagrande’s Apparatus
This test is done to determine index properties of soil for instance plastic limit, liquid limit, shrinkage limit. The results of this test are founded on the moisture content and the structure of the soil.
2.3 Liquid limit
Liquid limit of the soil is defined as the least moisture content at which the soil starts to flow. This test has been conducted in accordance with IS 2720(Part 5). The liquid limit apparatus is shown in Fig. 2.3. As the water given to soil increases there is a decrease in the shear strength and eventually, a moisture content is reached where the flow resistance of soil diminishes; this moisture content is known as the liquid limit which subsequently helps in the classification of fine-grained soil. The determination of liquid limit is important in order to calculate toughness and flow index.
Soil weighing about 120g and passing through 425 microns IS sieve is mixed with appropriate amount of water. A uniform paste is formed by mixing the water with soil thoroughly in an evaporating dish. Adequate portions of this paste are placed in the liquid limit cup and are cut into two halves by proper application of the Casagrande grooving tool. The handle of the apparatus then meticulously rotated at approximately 2 revolutions per second. The number of blows at which the 2 halves of the soil comes into contact with each other for the length of about ten mm is noted down. The soil sample is then taken for water content determination and the liquid limit is determined by plotting a graph of a number of blows against the water content. From the graph, the water content at 25 blows is selected as the liquid limit.
Plastic limit is that percentage of moisture present in the soil at which the soil sample mixed with appropriate amount of water is spun into threads of three mm diameter and cracks start to develop along the length of the thread and it breaks down into small pieces. In engineering practice, the plastic limit is defined as the minimum moisture content at which the soil changes its state from semisolid to plastic. If a thread of 3 mm diameter using a soil sample cannot be formed, then the soil is considered as nonplastic. This test was conducted in accordance with IS 2720 (Part 5) 1985. Soil weighing around 30 g and passing through 425 microns IS sieve is mixed with appropriate amount of water to form a paste. A small amount if this paste is taken and formed into a ball of small diameter which is then rolled on a clean glass plate so as to form a thin thread. If a thread of less than 3 mm diameter is rolled, it indicates that the moisture content present is greater than the plastic limit. This process is continuously repeated by making adjustments in the moisture content until a point is reached where the soil begins to crumble. The water content of the crumbled soil is then determined.
Shrinkage limit is defined as that percentage of moisture of the soil at which a further lowering in the moisture does not lead to change in the volume of the soil mass. It is the minimum water content at which the soil remains saturated. After a certain degree of shrinkage in a soil, the particles are so closely spaced that volume reduction will not take place further and hence further shrinkage ceases. Fig. 2.4 shows the oven dried soil pat. The shrinkage limit is that limit at which the soil passes from the semi-solid state to the solid state if moisture content is lowered. and is a means of describing the pore space present in a soil after it has been allowed to compact itself to the maximum density obtainable by shrinkage.
Fig. 2.4 Shrinkage limit soil pat
Hydrometer analysis is carried out in order to determine the particle size distribution in a soil with the sizes ranging from 75 microns to 0.01mm. Fig. 2.5 shows the hydrometer analysis of BCS. The data from this test is plotted on a semi-log graph of percentage finer against the diameter of the particles. This analysis is based on Stokes’ law which gives a connection among the velocity of fall of spheres in a fluid, diameter of the sphere, specific weights of the sphere and the fluid, and the fluid viscosity. About 50g of soil is taken and mixed with 100ml of dispersing agent in order to prepare a suspension. The suspension is again mixed with distilled water and stirred using a mechanical stirrer for around 5 minutes. This slurry is then transferred into a cylinder and filled with distilled water up to the 1000ml mark. The cylinder is then covered on the open end and is repeatedly turned upside down for about a minute to properly mix the constituents. The cylinder is then rested and the hydrometer is inserted in the cylinder and simultaneously a stopwatch is started. Hydrometer readings on the upper rim and the stem are noted after intervals of 0, 1, 2, 3 and 4 minutes. After 4 minutes, the hydrometer is detached and placed in a cylinder of 100ml dispersing agent and distilled water up to a 1000ml mark. Further readings are taken at 8, 15 and 30 minutes and also after 1, 2, 4, 8 and 24 hours. The hydrometer is placed just before taking the reading and is immediately removed. The temperature of the soil suspension is also noted down at each of the intervals.
Fig. 2.5 Hydrometer analysis of BCS
Standard Proctor test
Fig 2.6 Standard Proctor test
Standard Proctor test or Compaction test is a process to determine the optimum moisture content of a given soil sample, at optimum moisture content the soil sample becomes very dense and attains maximum dry density. It is a process in which densification occurs as the stress is applied to the soil. Standard Proctor test was conducted on different mixtures of soil, fly ash, crumb rubber, and cement. As the quantity of water is increased, dry density of soil increases initially then decreases. The maximum value of water content is called as Optimum moisture content and the dry density respective to the optimum moisture content is maximum dry density. The compaction test was conducted according to IS 2720 Part 7(1980). 3 kg of air-dried soil is taken in a pan. The soil passing through the 20 mm IS test sieve is taken for compaction test. A suitable amount of water is added to the sample so that the soil is properly damped. Now the soil is placed in the Proctor mold in three layers. Each layer is subjected to 25 blows using an automatic compaction apparatus as shown in Fig 2.6. The collar of the proctor mold is removed carefully and the top is leveled properly. A sample is kept in the oven for 24 hours to determine the moisture content of the soil sample. Now higher water content is added to the soil sample and the above steps are repeated. The procedure is repeated until the peak is obtained on the graph of moisture content against dry density. The optimum moisture content and the maximum dry density for different samples is determined by the respective graph. These values of optimum moisture content and maximum dry density obtained from the standard Proctor test are used to cast different specimens which are used for the determination of unconfined compressive strength.
Unconfined Compressive strength(UCS)
Fig 2.7 Unconfined Compressive Strength Test
The unconfined compressive test is one of the most economical methods for determining compressive strength and the sensitivity of the cylindrical sample of the soil. The samples of the unconfined compressive test are made using the results of standard Proctor test. Respective optimum moisture content is used for the making different samples. UCS was conducted as per the specifications provided in IS 2720 (Part X). An undisturbed cylindrical sample of the specimen is extruded from the sampling tube. The cylindrical sample having length 76 mm and diameter 38 mm is trimmed to get smooth ends. For different mixtures samples were prepared for 7, 14 and 28 days curing period in a humidity controlled environment. The samples were prepared by compacting 3 layers subjected to 25 blows in a standard compaction mold and then extracted using a UCS sample extruder. The soil sample is placed on the bottom plate of the loading device and the top plate is adjusted such that it is perfectly restrained on the top of the sample fig 2.8. The top plate is attached to the calibrated proving ring. The deformation and the proving ring dials are adjusted to zero and the axial load is applied at a strain rate of 0.5 to 0.2 % per minute. The load on the sample is increased gradually and the deformation and force applied values are noted periodically. The load is applied until the sample generates a failure surface or the deformation becomes excessive as shown in Fig 2.8. The data measured is used for the determination of the unconfined compressive strength. The maximum load observed per unit area is known as the unconfined compressive strength.
Fig. 2.8 UCS samples after failure
California Bearing Ratio
CBR test, an empirical test, has been used to determine the material properties for pavement design. The CBR is a measure of the resistance of a material to penetration of standard plunger under controlled density and moisture conditions. The laboratory CBR apparatus consists of a mold 150 mm diameter with a base plate and a collar, a loading frame and dial gauges for measuring the penetration values and the expansion on soaking.
The load is applied to the sample by a standard plunger with dia of 50 mm at the rate of 1.25 mm/min. A load penetration curve is drawn. The load values on standard crushed stones are 1370 kg and 2055 kg at 2.5 mm and 5.0 mm penetrations respectively. CBR value is expressed as a percentage of the actual load causing the penetrations of 2.5 mm or 5.0 mm to the standard loads mentioned above.
Two values of CBR will be obtained. If the value of 2.5 mm is greater than that of 5.0 mm penetration, the former is adopted. If the CBR value obtained from the test at 5.0 mm penetration is higher than that at 2.5 mm, then the test is to be repeated for checking. If the check test again gives similar results, then the higher value obtained at 5.0 mm penetration is reported as the CBR value. The average CBR value of three test specimens is reported as the CBR value of the sample.
Fig 2.9 California Bearing Ratio
MINI COMPACTION TEST
This test is performed basically for fine grained soil and requires very less amount of soil as compared to standard and modified proctor test. Its apparatus consists of cylindrical mould whose internal and external diameter as 3.80 and 4.60 cm respectively and 10 cm in height. The hammer weight of mini compaction is 1 kg and falling freely from approximate height of 16 cm.
For each test approximately 200g of fine grained soil is required which is mixed with required amount of water of content and mixed properly before pouring into compaction mould.
The soil is compacted in three layers and for each layer 36 blows are given. After each layer compacted surface is scratched with the help of knife in order to get good compaction.
After compacting three layers, excess of soil projecting out of the mould is trimmed off and removed with the help of knife.
Finally weight of compacted soil is taken for calculation of dry density of soil.
The above procedure is repeated again and again for different water contents and a dry density versus water content graph is plotted to determine the maximum dry density as well as optimum moisture content values.
Materials and Methodology
MATERIALS AND METHODOLOGY
Geotechnical properties of black cotton soil, lime and coir were determined by conducting different experiments. The properties of lime were provided by the supplier. Different geotechnical experiments were conducted such as standard Proctor test and unconfined compressive strength test after the determination of engineering properties of soil, lime and coir. This chapter includes all the experiments carried out to find out the geotechnical properties of the materials and it also includes methodology of carrying out the experiments on the mixtures prepared.
The materials which are used in this study are mentioned below:
Black cotton soil
2489200289560Black Cotton Soil:
Fig. 3.1 Black cotton soil
The black cotton soil was obtained from Davangere district, Karnataka at a depth of 1.5 m from the ground level. Fig. 3.1 shows the black cotton soil used for our experimental study. Table 3.1 includes the geotechnical properties of black cotton soil. As per Indian standard soil classification system (IS 1498-1970), the soil was classified as CH (inorganic clay of high plasticity). The engineering and index properties were assessed as per IS 2720.
Table 3.1 Geotechnical properties of soil
Experiments conducted Results
Specific gravity (IS 2720: Part 3) 2.6
Liquid limit (%) (IS 2720: Part 5) 60
Plastic limit (%) (IS 2720: Part 5) 19.75
Plasticity Index (IS 2720: Part 5) 40.25
Grain size distribution 2.5
Fine sand % Silt-size % 18.9
Clay size % 78.6
Soil classification CH (inorganic clay of high plasticity)
Shrinkage Limit (%) (IS 2720: Part 5) 9.32
Optimum moisture content (%) 21.8
Maximum dry unit weight (g/cc) 1.66
Unconfined compressive strength(N/mm2) 0.0549
California bearing ratio (%) 3.02
Fig 3.2 Lime (CaO)
Lime was obtained from Chemical house shop in Rajajinagar, Karnataka which is located at a distance of 12km from central Bengaluru. Fig. 3.2 shows the lime used in our investigation. Lime is used in the form of quicklime which is a caustic white alkali with the chemical name calcium oxide and is of white color. The physical and chemical properties of lime are given in Table 3.2
Table 3.2. Properties of lime
Chemical formula CaOMolar mass 56.077g/molAppearance White
Density 3.35 g/cubic cm
Boiling point 3123 K
Melting point 2845 K
Solubility in water Reacts
Solubility in acids Soluble
Solubility in methanol Insoluble
Crystal structure Face-centered cubic structures
Fig 3.3. Coir Fiber
The coir fiber shown above in figure 3.3 used was cut and extracted from used coconut shells of Rajarajeshwari temple. Obtained coir fiber was left to dry in sunlight for 1 day. It was further cut into the length of 2.5cm with a diameter of 0.02mm, having an aspect ratio of 1250. The properties of coir fiber are shown below in Table 3.3.
Table 3.3. Properties of coir fiber
Chemical properties % Composition
Pectin’s and related compounds 03.01
Water soluble 05.26
Physical Properties Value
Length in inches 6-8
Breaking elongation 30
Rigidity of modulus(dyne/cm2) 1.8924
Swelling in water(diameter) 5%
METHODOLOGY AND PREPARATION OF MIXES:
In order to stabilize the black cotton soil which tends to swell and shrink under different moisture conditions and to improve its physical as well as engineering properties, the entire experimental study is going to be preferred as a series of following steps.
The literature review will be done on the topic of “Stabilization of Black Cotton Soil using lime and coir fibers” by collecting and studying related journals.
Literature gap will be pointed out after the thorough study of journals, which will provide the main objective of our experimental study.
Materials needed for the study will be acquired from respective suitable sources.
Characteristics of material, in this case of the black cotton soil, will be determined by performing a series of experiments such as atterberg limits, compaction tests, unconfined compression test, etc.
The content of lime will be varied in terms of percentage by weight in different proportions ranging 0%,2%,4%,6% in the consecutive samples at their respective optimum moisture content which would be determined by mini compaction test.
CBR tests and UCS tests will be carried on different soil samples carrying different proportions of lime by weight which will, in turn, lead us to the optimum lime content required by black cotton soil for stabilization.
Subsequently, keeping the optimum lime content at a constant value coir fiber are added to the soil samples for carrying out CBR as well as UCS tests to determine the optimum coir content.
Finally, optimum lime and coir content required for the stabilization of black cotton soil is obtained.
Figure 3.4 Methodology
Results and Discussion
RESULTS AND DISCUSSION
A set of usual laboratory test procedures such as the Compaction test, CBR test, and UCS test was carried out on a number of specimen-derived by various combinations of the materials that are used in this study. The effects of the addition of these materials and the results of the tests have been discussed in this chapter.
EFFECT OF LIME ON BLACK COTTON SOIL
EFFECT OF LIME ON THE COMPACTION CHARACTERISTICS OF BLACK COTTON SOIL
The test was carried out by varying the lime content. The values obtained are shown in Table 4.1. Fig. 4.1 represents the effect of lime on the compaction characteristics of black cotton soil Fig 4.2 and 4.3 shows variation of OMC and MDD of BCS on the addition of lime. The percentage of lime used has been varied in the amount of 0%, 2.0%, 4.0% and 6.0% by weight of expansive soil. The dry density of the soil decreases as the amount of lime is increased. The maximum dry density decreases from 1.73 g/cc for 0% lime to 1.59 g/cc for 6% lime.It is due to the light specific gravity as well as lightweight nature of lime. It was also observed that with the addition of lime optimum moisture content increases. It increases from 20.80% for 0% lime to 24.30% for 6% lime. The main reason behind this is due to the water absorption of lime.
Table 4.1 Variation of OMC and MDD with Lime
Lime Content Optimum Moisture Content (%) Maximum Dry Density (g/cc)
B.C.S + 0 % Lime 20.8 1.73
B.C.S + 2 % Lime 22.5 1.67
B.C.S + 4 % Lime 23.2 1.65
B.C.S + 6 % Lime 24.3 1.59
Fig. 4.1 Compaction curve of BCS treated with varying percentages of lime.
Fig.4.2 Variation of MDD of BCS on the addition of lime.
Fig. 4.3 Variation of OMC of BCS on the addition of lime.
Effect of lime on CBR of black cotton soil
Fig 4.4 represents the effect of lime on CBR of black cotton soil. The CBR value of black cotton soil mixed with varying lime content is shown in the figure. The lime content was varied for 0%, 2%, 4% and 6%. Table 4.2 shows the variation of CBR for various lime content. As the lime content in the soil increases CBR value of the soil also increases.
Table 4.2 Variation of CBR with increasing percentage of lime.
Lime Content CBR Value
B.C.S + 0 % lime content 3.02
B.C.S + 2 % lime content 5.76
B.C.S + 4 % lime content 7.5
B.C.S + 6 % lime content 6.9
Fig.4.4 Variation of CBR of Black Cotton Soil with lime.
Effect of lime on UCS of black cotton soil
Fig 4.5 represents the effect of lime on the unconfined compressive strength of expansive soil. The unconfined compressive strength test results of black cotton soil mixed with 4% lime by weight of soil and cured for 7 days is shown in the figure. Table 4.3 shows the variation of UCS. The addition of lime is found to increase the unconfined compressive strength significantly for 7 days curing period.
Table 4.3 Variation of UCS
Particulars 7 days strength
BCS + 0% lime 54.9 kPa BCS + 2% lime 127 kPa
`Fig.4.5 Variation of UCS of Black Cotton Soil on the addition of lime.
EFFECT OF COIR FIBRE ON BLACK COTTON SOIL
EFFECT OF COIR FIBRE ON THE COMPACTION CHARACTERISTICS OF BLACK COTTON SOIL
Fig.4.6 represents the effect of coir fiber on the compaction characteristics of black cotton soil mixed with optimum lime content, i.e, 4%. Table 4.4 shows the variation OMC and MDD with coir fiber. Fig 4.7 and Fig. 4.8 shows the variation of MDD and OMC of BCS with optimum lime with the addition of coir fiber respectively. The percentage of coir fiber used has been varied in the amount of 0%, 0.25%. 0.5%, 0.75% and 1% by weight of soil. The dry density of the soil decreases with increase in the coir fiber content. The maximum dry density achieved was 1.65 g/cc. The MDD goes on decreasing with the addition of coir fiber due to the low density of the coir. The OMC has been observed to increase with the addition of coir content. This is because the coir fiber tends to absorb the water. The maximum OMC was found to be 24.2%.
Table 4.4 Variation of OMC and MDD with coir fiber.
Coir Fibre Content Optimum Moisture Content (%) Maximum Dry Density (g/cc)
0 % coir content 23.2 1.65
0.25 % coir content 23.6 1.63
0.5 % coir content 23.9 1.62
0.75 % coir content 24.1 1.60
1 % coir content 24.2 1.59
Fig. 4.6 Compaction curve of BCS treated with varying percentages of coir fiber
Fig.4.7 Variation of MDD of BCS on the addition of coir fiber.
Fig. 4.8 Variation of OMC of BCS on the addition of coir fiber.
Effect of coir fiber on CBR of black cotton soil
Fig 4.9 represents the effect of coir fiber on California Bearing Ratio of black cotton soil. The CBR value of black cotton soil and optimum lime mixed with varying coir fiber content is shown in the figure. The coir fibre content was varied for 0%, 0.25%, 0.5%, 0.75% and 1%. Table 4.5 shows the variation of CBR for varying coir fiber content. The addition of coir fiber is found to increase the California bearing ratio.
Table 5.5 Variation of CBR with coir fiber.
Coir Content CBR Value
0 % coir content 7.50
0.25 % coir content 10.63
0.5 % coir content 12.03
0.75 % coir content 12.87
1 % coir content 13.83
Fig.4.9 Variation of CBR of Black Cotton Soil with coir fiber.
Effect of coir fiber on UCS of black cotton soil.
Fig 4.10 represents the effect of coir fiber on the unconfined compressive strength of black cotton soil. The unconfined compressive strength test results of black cotton soil mixed with a different percentage of coir fiber and cured for 7 days is shown in the figure. Table 4.6 shows the variation of UCS for different coir content. The addition of coir fiber initially increases the unconfined compressive strength of the BCS till 0.5% coir fiber where it achieves maximum UCS of 195 KPa. After this point, the UCS starts decreasing on the addition of coir fiber.
Table 4.6 Variation of UCS with coir content
Particulars 7 days
BCS+ 4% lime + 0% coir fibre 127 kPa BCS+ 4% lime + 0.25% coir fibre 176.5 kPa BCS+ 4% lime + 0.5% coir fibre 195 kPa BCS+ 4% lime + 0.75% coir fibre 143 kPa BCS+ 4% lime + 1% coir fibre 125 kPa
Fig.4.10 Variation of UCS of Black Cotton Soil on the addition of coir fiber.
Comparison for the addition of lime and coir
4.3.1. Comparison of CBR for optimum lime and optimum coir fiber content.
Fig 4.11 shows the comparison between the California Bearing Ratio for black cotton soil with optimum lime content and optimum coir fiber content. On addition of optimum lime content, there is a significant increase in the California Bearing Ratio and the addition of optimum coir fiber content also increases the UCS slightly.
Fig.4.11 Variation of CBR of Black Cotton Soil with optimum lime and
optimum coir fiber content.
4.3.2. Comparison of UCS for optimum lime and optimum coir fiber content.
Fig 4.12 shows the comparison between the unconfined compressive strength for black cotton soil with optimum lime content and optimum coir fiber content. On addition of optimum lime content, there is a significant increase in the unconfined compressive strength and the addition of optimum coir fiber content also increases the UCS significantly.
Fig.4.12 Variation of UCS of Black Cotton Soil with optimum lime and
optimum coir fiber content.
A comprehensive laboratory study was done to determine the characteristics and characterization of the Black cotton soil, standard Proctor test, mini compaction test, California bearing ratio (CBR) tests along with unconfined compression tests were carried out to study the influence of lime and coir fiber on the black cotton soil. The conclusions obtained are mentioned as follows:
1. The optimum moisture content (OMC) increased from 20.80% for 0% lime to 24.30% for 6% lime. The main reason for this is due to water absorption of lime.
2. The maximum dry density (MDD) upon addition of lime decreased slightly from 1.73g/cc for 0% lime to 1.59g/cc for 6% lime. The main reason for this is due to low specific gravity of lime.
3. The optimum lime content found to be 4%by weight of soil.
4. The optimum moisture content increased from 23.2% for 0% coir content to24.2% for 1% coir content. This is because the coir fiber tends to absorb the water.
5. The maximum dry density (MDD) upon fixing of 4% (optimum lime content) and the addition of coir fiber decreased slightly from 1.65g/cc for 0% coir fiber to 1.59g/cc for 1%coir fiber.
6. The addition of coir fiber with optimum lime content initially increased the unconfined compressive strength (UCS) for 7 days tests from 127kPa to 195kPa till 0.5% coir fiber and after this, it decreased to 125kPa for 1% coir fiber.
7. The optimum coir content found to be 0.5% by weight of soil.
8. The California bearing ratio (CBR) increased from 3.02 for 0% lime to 7.5 for 4% lime with the addition of only lime.
9. The California bearing ratio (CBR) upon fixing of 4% (optimum lime content) and the addition of coir fiber increased from 7.50 for 0% coir content to 13.83 for 1% coir content.
10. The California bearing ratio (CBR) of only black cotton soil was 3.02 and with the addition of optimum lime content, it increased to 7.5. Finally with the addition optimum lime content and optimum coir content, its value increased to 12.03.