PROJECT REPORT on STUDY OF STABILIZATION OF BLACK COTTON SOIL USING LIME
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With the increasing of population and the reduction of available land, more and more construction of buildings and other civil engineering structures have to be carried out on weak or soft soil. Owing to such soil of poor shear strength and high swelling & shrinkage, a great diversity of ground improvement techniques such as soil stabilization and reinforcement are employed to improve mechanical behaviour of soil, thereby enhancing the reliability of construction. There are several techniques have been researched up till now whether it may be using lime, fly ash, or certain add-mixtures. As a good stabilizing agent, lime is extensively applied in soil stabilization of foundation or roadbed. However, lime-treated soil is susceptible to high rigidity and hence the characteristic of brittle failure which is the hidden trouble in engineering construction.
The study proceeds in such a way that a soil sample will be collected from the areas near our college in Jhansi that will be the BLACK COTTON soil .In most of the areas of BUNDELKHAND and MADHYA PRADESH black cotton soil is found so we will consider this soil as a subject of our study. Soil sample is tested barely without any mixture of lime and then it will be tested after addition of lime at certain amounts of lime like at 5%, 10%, 15% and the results study will be done after these tests. A series of basic tests will be practised like liquid limit test, penetration test, fineness test, shear tests, etc. The outcome of these tests will be helpful to make study that using lime will be a best and cheap method of ground improvement.
Soil is the indispensable element of this nature. It is attached to everyone in one or another way. All the basic amenities of life, whether it is concerned with food, clothes and house, have been fulfilled by the soil .Without the soil it is just next to impossible to think about life on this earth.
The word ‘soil’ is derived from the Latin word solium which according to Webster’s dictionary means the upper layer of the earth that may be dug or plowed; specifically, the loose surface material of earth in which plant grows. The top soil contains a large organic quantity matter and is not suitable as a construction material or as a foundation for structures.
The term soil in soil engineering is defined as an unconsolidated material, composed of solid particles produced by disintegration of rocks. The voids space between particles may contain air, water or both. The solid particles may contain organic matter. The soil particles maybe separated by such mechanical means as agitation and water.
Soil deposits in nature exist in an extremely erratic manner producing thereby an infinite variety of possible combination which will affect the strength of the soil and the procedures to make it purposeful. So is the particular case of black cotton soil with a wide range of challenges associated with the construction at sites with black cotton soil. The engineering behaviour of a soil mass is expected to be greatly influenced by the mineral composition of the soil grains forming the soil mass. This, however, is only partly true. In case of coarse grained soil, the mineralogical composition of the grain hardly affects the engineering properties of the soils perhaps the grain to grain friction is influenced to a degree. Is such soils, inter particle forces other than those due to gravity are of no consequence, but the finer particles, the more significant becomes the forces associated with the surface area of the grains. The chemical character of the individual grain assumes importance especially when the surface area is large related to the size of the grain - a condition which is associated with the fine grained soil. Thus, inter-particle attraction holding the grain together becomes increasingly important as the size decreases.
The soil structure means the mode of arrangement of soil particles related to each other and the forces that are acting between soil particles to hold them together in their positions. The concept is further extended to include the mineralogical composition of the grains, the electrical properties of the particle surface, the physical characteristics, ionic composition of pore water, the interactions among the soil particles, pore water and the adsorption complex.
Effects of addition of lime on Black Cotton Soil
Martin Jacob and K.Pandeu conducted a series of lab tests and evaluated the effects of hydrated lime on the engineering behaviour of highly plastic clay soil. Tests were performed with different percentages of hydrated lime. On the basis of all tests and their results they concluded:
Effects of lime (6 % addition of lime) on Atterberg Limits: The plasticity index values of the clay soil are substantially and immediately decreased with increasing lime content; no significant effect of curing time is noted; the large increase in the plastic limit thus increasing the granular nature of the clay with lime.
Effect of lime surface areas obtained by the methylene lime method (8 % addition of lime): Increasing the lime content and curing time decreases the surface areas of the treated soil; 20 % added lime decreases 40 % in surface area.
MATERIALS TO STUDY THE BLACK COTTTON SOIL
Black Cotton Soil
Black cotton soil (BC soil) is a highly clayey soil. The black colour in Black cotton soil (BC soil) is due to the presence of titanium oxide in small concentration. The Black cotton soil (BC soil) has a high percentage of clay, which is predominantly montmorillonite in structure and black or blackish grey in colour. Expansive soils are the soils which expand when the moisture content of the soils is increased. The clay mineral montmorillonite is mainly responsible for expansive characteristics of the soil. The expansive soils are also called swelling soils or black cotton soils.
The structures 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. The physical properties of Black cotton soil (BC soil) vary from place to place 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. Research & Development (R&D) efforts have been made to improve the strength characteristics of Black cotton soil (BC soil) with new technologies. The construction of foundation for structure on black cotton soils poses challenge to civil engineers.
Formation of minerals
The combination of two sheets of silica and gibbsite in different arrangements and conditions lead to the formation of different clay minerals given in above Table. In the actual formation of the sheet silicate minerals, the phenomenon of isomorphous substitution frequently occurs. Isomorphous (meaning same form) substitution consists of the substitution of one kind of atom for another.
Montmorillonite is the most common mineral of the montmorillonite group. The structural arrangement of this mineral is composed of two silica tetrahedral sheets with a central alumina octahedral sheet. All the tips of the tetrahedral point in the same direction and toward the center of the unit. The silica and gibbsite sheets are combined in such a way that the tips of the tetrahedrons of each silica sheet and one of the hydroxyl layers of the octahedral sheet form a common layer. The atoms common to both the silica and gibbsite layer become oxygen instead of hydroxyls. The thickness of the silica-gibbsite-silica unit is about 10 Å.
Black Cotton Soil- Peculiar Characteristics
Black Cotton soil (BC soil) is a highly clayey soil. It is so hard that the clods cannot be easily pulverized for treatment for its use in any construction. This poses serious problems as regards to subsequent performance of the structure. Moreover, the softened soil beneath has a tendency to up heave into the upper layers of the foundation, especially when the bottom layers consists of stone soling with lot of voids. Gradual intrusion of wet Black cotton soil (BC soil) invariably leads to failure of the structure.