STABILIZATION OF SOIL USING CHEMICAL METHODS

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1 STABILIZATION OF SOIL USING CHEMICAL METHODS 1 P.DURGA BHAVANI, 2 Dr. D S V PRASAD 1 PG student dept. Of civil Engg, BVC Engineering College, Odalarevu, 2 M.E, Ph.D., MIE, MISTE, MIGS Professor & Principal, Dept. of Civil Engg., BVC Engineering College, Odalarevu, AP Abstract: - In India, expansive soils popularly known as black cotton soils are highly problematic, as they swell on absorption of water and shrink on evaporation thereof. Because of this alternate swell and shrinkage, distress is caused to the foundations of structures laid on such soils. Understanding the behavior of expansive soil and adopting the appropriate control measures have been great task for the geotechnical engineers. Extensive research is going on to find the solutions to black cotton soils. There have been many methods available to controlling the expansive nature of the soils. Treating the expansive soil with electrolytes is one of the techniques to improve the behavior of the expansive ground. Hence, in the present work, experimentation is carried-out to investigate the influence of electrolyte viz. potassium chloride, calcium chloride and ferric chloride on the properties of expansive soil. A methodical process, involving experimentation on Atterberg limis (liquid limit, plastic limit), sieve Analysis, specific gravity, proctor compaction test, California Bearing Ratio(CBR), Unconfined Compressive Strength(UCS) test, Triaxial test were conducted by adding 0.5%, 1%, 1.5% of Potassium Choride, Calcium Chloride and Ferric Chloride to the expansive soil by dry weight under controlled conditions in the laboratory. It is observed form the laboratory studies that maximum reduction in properties is observed for Ferric Chloride treatment compared to other electrolytes tried in this investigation. I. INTRODUCTION Expansive soil is one among the problematic soils that has a high potential for shrinking or swelling due to change of moisture content. Expansive soils can be found on almost all the continents on the Earth. Destructive results caused by this type of soils have been reported in many countries. In India, large tracts are covered by expansive soils known as black cotton soils. The major area of their occurrence is the south Vindhyachal range covering almost the entire Deccan Plateau. These soils cover an area of about 200,000 square miles and thus form about 20% of the total area of India. The primary problem that arises with regard to expansive soils is that deformations are significantly greater than the elastic deformations and they cannot be predicted by the classical elastic or plastic theory. Movement is usually in an uneven pattern and of such a magnitude to cause extensive damage to the structures resting on them. Proper remedial measures are to be adopted to modify the soil or to reduce its detrimental effects if expansive soils are indentified in a project. The remedial measures can be different for planning and designing stages and post construction stages. Many stabilization techniques are in practice for improving the expansive soils in which the characteristics of the soils are altered or the problematic soils are removed and replaced which can be used alone or in conjunction with specific design alternatives. Additives such as lime, cement, calcium chloride, rice husk, fly ahs etc. are also used to alter the characteristics of the expansive soils. The characteristics that are of concern to the design engineers are permeability, compressibility and durability. The effect of the additives and the optimum amount of additives to be used are dependent mainly on the mineralogical composition of the soils. The paper DOI: /IJRTER BNXRM 104

2 focuses about the various stabilization techniques that are in practice for improving the expansive soil for reducing its swelling potential and the limitations of the method of stabilization there on. Chemical modification by adding lime and lime-pozzolan mixes has been practiced for the last two decades. However, due to low solubility (about 1.2 of lime and mixing problems involved, use of strong electrolytes like KCl, CaCl2 and FeCl3 were tried by various researchers. Further, a group of researchers reported that CaCl2 could be an effective alternative to conventional lime treatment due to its ready dissolvability to supply adequate calcium ions for exchange reactions. In this work it is attempted to study the effect of electrolytes like KCl, CaCl2 and FeCl3on the properties of expansive soil. 1.1 OBJECTIVE The objective of the present work is to study the impact of the electrolytes like KCl, CaCl2 and FeCl3on the properties of expansive soil in laboratory 1.2 SOIL STABILIZATION Stabilization of soil in a broader sense is the modification of the properties of a soil is improving its engineering performance. Soil stabilization is broadly used in connection with road, pavement and foundation construction. It improves the engineering properties of the soil in terms of volume stability, strength, and durability. 3 Soil stabilization occurs over a longer time period of curing. A soil that is treated with ground granulated blast furnace slag is modified and its properties are changed which may lead to stabilization. When sufficient amount of ground granulated blast furnace slag is added to the soil, stabilization occurs. Stabilization is different than modification as strength increases. 1.3 TYPES OF STABILIZATION There are different types of stabilization, each having its own benefits and potential problems. The types described below are those most frequently used. 1.4 Mechanical Stabilization The most basic form of mechanical stabilization is compaction, which increases the performance of a natural material. The benefits of compaction however are well understood and so they will not be discussed further in this report. Mechanical stabilization of a material is usually achieved by adding a different material in order to improve the grading or decrease the 3 plasticity of the original material. The physical properties of the original material will be changed, but no chemical reaction is involved. For example, a material rich in fines could be added to a material deficient in fines and in order to produce a material nearer to an ideal particle size distribution curve. This will allow the level of density achieved by compaction to be increased and hence improve the stability of the material under traffic. The proportion of material added is usually from 10 to 50 per cent. Mechanical stabilization is usually the most cost-effective process for improving poorly-graded materials. This process is usually used to increase the strength of poorly-graded granular material up to the well-graded granular material. The stiffness and strength will generally be lower than that achieved by chemical stabilization and would often be insufficient for heavy traffic pavements. It may also be necessary to add a stabilizing agent to improve the Final properties of the mixed material. 1.5 Cement Stabilization: - Any cement can be used for stabilization, but Ordinary Portland cement is the most widely used throughout the world. The addition of cement material, in the 4 presence of moisture, produces All Rights Reserved 105

3 calcium aluminate and silicate gels, which crystallize and bond the material particles together. Most of the strength of a cement-stabilized material comes from the hydrated cement. A chemical reaction also takes place between the material and lime, which is released as the cement hydrates leading to a further increase in strength. Granular materials can be improved by the addition of a small proportion of Portland cement, generally less that 10 per cent. The addition of more than 15 per cent cement usually results in conventional concrete. In general the strength of the material will steadily increase with a rise in the cement content. There are three main types of cement stabilized materials:- (a) Soil Cement Soil cement usually contains less than 5 per cent cement. It can be either mixed in-situ (usually up to 300mm layer at a time) or mixed in plant. The technique involves breaking the soil sample and mixing in the cement, then adding water and compacting in the usual way. In (1998) croney recommends that a minimum strength should be 2.5 Mpa (7 days cube crushing strength) or, if this material is used to replace the sub-base then strength requirement should be increased to 4 MPa. 4 (b) Cement Bound Granular Material (CBM) Cement bound granular Material (CBM) This can be regarded as a stronger form of soil-cement which uses granular aggregate (crushed rock or natural gravel) rather than a soil. The process works best if the natural granular material has limited fines content. This is always mixed in plant and the strength requirement is 5-7 MPa (7 days cube crushing strength). (c) Lean Concrete This material has low cement content and hence looks and behaves as concrete of a CBM. It is usually made from batched coarse and fine crushed aggregate, but natural washed aggregate (e.g. river gravels) can also be used Lime Stabilization:- The stabilization of pavement materials is not new, with examples of lime stabilization being recorded in the construction of early Roman roads. However, the invention of Portland cement in the 19th Century resulted in cement replacing lime as the main type of stabilizer. Lime stabilization will only be effective with materials which contain enough clay for a positive reaction to take place. Lime is produced from chalk or limestone by heating and combining with water. The term lime is broad and covers the following three main types: a) Quicklime i.e. calcium oxide (CaO), b) Slaked or hydrated lime, i.e. calcium hydroxide Ca(OH) 2 and c) Carbonate of lime, i.e. calcium carbonate (CaCO3). Only quicklime and hydrated lime are used as stabilizers in road construction. They are usually added in solid form but can also be mixed with water and applied as slurry. It must be noted that there is a violent reaction between quicklime and water and consequently operatives exposed to quicklime can experience several external and internal burns, as well as blinding. Hydrated lime is used extensively for the stabilization of soil, especially soil with a high clay content where its main advantage is in raising the plastic limit of the clayey soil. Very rapid stabilization of water-logged sites has been achieved with the use of quicklime. 1.7 Bitumen or Tar Stabilization Bitumen or tar are too viscous to use at ambient temperatures and must be made into either cut-back bitumen (a solution of bitumen in kerosene or diesel) or a bitumen emulsion (bitumen particles suspended in water). When the solvent evaporates or the emulsion breaks the bitumen is deposited on the material, the bitumen merely acts as a glue to stick the material particles together and prevent All Rights Reserved 106

4 ingress of water. In many cases the bituminous material acts as an impervious layer in the pavement, preventing the rise of capillary moisture. In a country where bitumen is relatively expensive compared to cement and where most expertise is in cement construction, it appears more reasonable to use a cement stabilizer rather than a bitumen/tar based product Geosynthetic Stabilization Geosynthetic in general can be defined as a generic term which includes geotextiles, geomembranes, geocomposites and these material used by civil engineers to improve soil behaviour. The American society for Testing and materials has defined geosynthetics as a product manufactured from polymeric materials. Earth and any other geotechnical engineering materials is an integral part of manmade project and structures. Geosynthetics are almost exclusively manufactured from polymeric materials such as polypropylene, polyester, and polyethylene. 1.9 Chemical Stabilization Stabilization of moisture in soil and cementation of particles may be done by chemicals such as calcium chloride, sodium chloride etc. Although all the method is well versed for the soil stabilization but these all require money to spend. II. METHODOLOGY 2.1 MATERIALS A. Soil The black cotton soil collected from Morampalem village near Amalapuram, E.G.Dt., AP, India. The properties of the soil are given in Table 2.1. Table 2.1: Properties of Expansive All Rights Reserved 107

5 2.2 CHEMICALS USED Commercial grade KCl, CaCl2 and FeCl3 are used for this study. The quantity of the chemical was varied from 0 to 1.5% by dry weight of soil. Plate 2.1: Ferric Chloride Plate 2..2: Calcium Chloride Plate 2.3: Potassium Chloride 2.3. Laboratory Experimentation A. Atterberg Limits Liquid Limit Different percentages of chemical ranging from 0-1.5% by dry weight are mixed with the soil and the liquid limit were determined as per IS: 2720 (part-5) Plastic Limit Different percentages of chemical ranging from 0-1.5% by dry weight are mixed with the soil and the plastic limit were determined as per IS: 2720 All Rights Reserved 108

6 Shrinkage limit Different percentages of chemical ranging from 0-1.5% by dry weight are mixed with the soil and the shrinkage limit were determined as per IS: 2720 (part-6) Compaction Properties Optimum moisture content and maximum dry density of the Expansive soil were evaluated as per IS Heavy weight compaction test (IS: 2720 part-8, 1983). Differential Free Swell (DFS The DFS test for all the combinations has been conducted as per IS code of practice (IS:2720-part XL- 1977). B. Strength Tests Tri-axial test, California bearing ratio& Unconfined Compressive Strength values were found for all the soil combinations, as presented below. 29 Sample Preparation Both treated and untreated samples were prepared by compacting different mixes to the maximum dry density of the soil. The initial moisture content for these samples was maintained at optimum moisture content of the untreated soil. The amount of chemical to be added to the amount of water was arrived at based on the optimum moisture content of the natural soil and the chemical solution was prepared. This solution was added to the dry soil and the mixture was thoroughly mixed. Plate 2.4: Samples Curing In Desiccators Tri-Axial test The tri-axial tests (as per) were conducted on all the combinations listed in table. At the end of the respective curing period (the samples were cured for 1 day, 7 days, and 14 days after All Rights Reserved 109

7 Plate 2.5: Samples Cured For 1, 7, 14 All Rights Reserved 110

8 Plate 2.6: Samples after Failure Sample Preparation Both treated and untreated samples were prepared by compacting different mixes to the maximum dry density of the soil. The initial moisture content for these samples was maintained at optimum moisture content of the untreated soil. The amount of chemical to be added to the amount of water was arrived at based on the optimum moisture content of the natural soil and the chemical solution was prepared. This solution was added to the dry soil and the mixture was thoroughly mixed. California Bearing Ratio Test The California bearing ratio tests (as per IS: 2720 (part-16)-1979) were conducted on all the combinations listed in table.. At the end of the curing period (all the samples were cured for 3 days and later soaked for 4 days). Plate 2.7: Test Setup for CBR All Rights Reserved 111

9 Sample Preparation Both treated and untreated samples were prepared by compacting different mixes to the maximum dry density of the soil. The initial moisture content for these samples was maintained at optimum moisture content of the untreated soil. The amount of chemical to be added to the amount of water was arrived at based on the optimum moisture content of the natural soil and the chemical solution was prepared. This solution was added to the dry soil and the mixture was thoroughly mixed. Unconfined Compressive Strength The various mixes of soil and additives in different proportions are fixed at water content corresponding to OMC values of each mix and the samples are prepared for conducting Unconfined Compressive Strength test for each proportion in the constant volume mould. These samples are cured for 1 day, 7 days and 14 days. After the period of curing, these samples are tested for unconfined compressive strength test as per IS code of practice (IS:2720, 1664). III. DISCUSSION ON TEST RESULTS Details of the laboratory experimentation carried-out with chemical stabilization have been discussed in the previous chapter. In this chapter a detailed discussion on the results obtained from various laboratory were presented. 3.1 LABORATORY TEST RESULTS ON CHEMICAL STABILIZATION The effect of adding different chemicals to the expansive soil on Atterberg limits, DFS and Strength Properties are discussed in the following sections Table 3.1: Effect of Chemical on Index Properties of Expansive All Rights Reserved 112

10 Fig 3. A: Variation of Liquid Limit with Different Percentage Chemicals Blending in Expansive Soil Fig 3.B: Variation of Plastic Limit with Different Percentage Chemicals Blending in Expansive All Rights Reserved 113

11 Fig 3.C: Variation of Plasticity Index with Addition of Percentage Chemicals Fig 3.D: Variation of Shrinkage Limit with Addition of Percentage Chemicals Blending In Expansive Soil The variation of liquid limit values with different percentages of chemicals added to the expansive soil is presented in the Fig.4.a. It is observed that the decrease in the liquid limit is significant upto 1% of chemical added to the expansive clay for all the chemicals, beyond 1% there is a nominal decrease. Maximum decrease in 35 liquid limit for stabilized expansive clay is observed with the chemical FeCl3, compared with other two chemicals, KCl and CaCl2. Nominal increase in plastic limit of stabilized expansive clay is observed with increase the percentage of the chemical All Rights Reserved 114

12 Table 3.2: Effect of Chemicals on DFS of Expansive Soil Fig.3.c shows the variation of plasticity index with the addition of chemicals to expansive clay. The increase in the plastic limit and the decrease in the liquid limit cause a net reduction in the plasticity index. It is observed that, the reduction in plasticity indexes are 26%, 41% and 48% respectively for 1 % of KCl, CaCl2 and FeCl3 added to the expansive clay. The reduction in plasticity index with chemical 36 treatments could be attributed to the depressed double layer thickness due to cation exchange by potassium, calcium and ferric ions. The variation of shrinkage limit with the percentage of chemical added to the expansive soil is presented in the Fig.4.d. With increase in percentage of chemical added to the expansive soil the shrinkage limit is increasing. With 1.5 % chemical addition, the shrinkage limit of stabilized expansive clay is increased from 12% to 15.1%, 15.4% and 16% respectively for KCl, CaCl2 and FeCl3. Fig 3.E: Variation of DFS for Different Chemicals Blending In Expansive Soil Fig 3.E: Variation of DFS for Different Chemicals Blending In Expansive Soil. Effect of Additives on All Rights Reserved 115

13 Soaked CBR Values International Journal of Recent Trends in Engineering & Research (IJRTER) The variation of DFS of stabilized expansive clay with addition of different percentages of chemicals is shown in the Fig.4.e. It is observed that the DFS is decreasing with increasing percentage of chemical added to the expansive soil. Significant decrease in D.F.S. is recorded in stabilized expansive clay with addition of 1% of chemical. The reductions in the DFS of stabilized expansive clay with addition of 1% chemical are 40%, 43% and 47% for KCl, CaCl2 and FeCl3 respectively compared with the expansive clay. The reduction in DFS values could be supported by the fact that the double layer thickness is suppressed by cation exchange with potassium, calcium and ferric ions and with increased electrolyte concentration. 37 Table 3.3: Effect of Chemicals on CBR of Expansive Soil % Of Chemicals Potassium Chloride Calcium Chloride Ferric Chloride Fig 3.F: Variation of CBR of Stabilized Expansive Soil with Percentage of All Rights Reserved 116

14 3.2 Effect of Additives on CBR Fig.4.f. shows the variation of CBR of stabilized expansive clay with addition of different percentages of chemicals. It is can be seen that the CBR is increasing with increasing percentage of chemical added to the expansive soil. Significant increase in CBR is recorded in stabilized expansive clay with addition of chemical upto 1%, beyond this percentage the increase in CBR is marginal. The increase in CBR values of stabilized expansive clay with addition of 1% chemical are 80%, 99% and 116% for KCl, CaCl2 and FeCl3 respectively compared with the expansive clay. The increase in the strength with addition of chemicals may be attributed to the cation exchange of KCl, CaCl2 & FeCl3between mineral layers and due to the formation of silicate gel. The reduction in improvement in CBR beyond 1% of chemicalskcl, CaCl2 & FeCl3, may be due to the absorption of more moisture at higher chemical content. Table 3.4: Variation of Shear Strength Parameters with the Addition of Chemicals to Expansive Soil 3.3 Effect of Additives on Shear Strength Properties The undrained shear strength parameters of the remoulded samples prepared at MDD and optimum moisture content with addition of 0.5%, 1% and 1.5 % of chemicals, KCl, CaCl2 & FeCl3, to the expansive soil are presented in the table 4.5. The prepared samples are tested after 1day, 7 days and 14 days. Significant change in undrained cohesion and marginal change in angle of internal friction is observed with addition of chemicals to the expansive clay. The increase in the shear strength parameters with addition of chemicals may be attributed to the cation exchange of chemicals. The shear strength parameters are increases upto 1 % chemical addition of above three chemicals, beyond this percentage there is a considerable decrease is observed may be due to the absorbtion of more moisture at higher chemical All Rights Reserved 117

15 Table 3.5: Variation of Undrained compressive strength of stabilized expansive clay Fig 3.g: Variation of UCS for 1day All Rights Reserved 118

16 Fig3.h: Variation of UCS for 7 days curing Fig3.i: Variation of UCS for 14 days curing 3.4 Effect of Additives on Shear Strength Properties The unconfined compressive strength of the remoulded samples prepared at MDD and optimum moisture content with addition of 0.5%, 1% and 1.5 % of chemicals, KCl, CaCl2 & FeCl3, to the expansive soil are presented in the table 4.6. The prepared samples are tested after 1day, 7 days and 14 days. As expected, the unconfined compressive strength is increasing with time may be due chemical reaction. It is observed that the unconfined compressive strength of the stabilized expansive soil is increasing with increase in percentage of chemical added to the soil.the unconfined compressive strength of stabilized expansive clay is increased by 133%, 171% & 230% when treated with 1% All Rights Reserved 119

17 chemical, of KCl,CaCl2 and FeCl3 respectively. The increase in the strength with addition of chemicals may be attributed to the cation exchange of KCl,CaCl2& FeCl3between mineral layers and due to the formation of silicate gel. The reduction in strength beyond 1% each of KCl, CaCl2 & FeCl3 may be due to the absorption of more moisture at higher KCl, CaCl2 & FeCl3. The optimum percentage of different additives observed during the laboratory experimentation are summarized and presented in the following Table Optimum percentage of different additives 3.7. Additives Optimum percentage KCl CaCl2 FeCl IV. CONCLUSIONS The following conclusions can be drawn from the laboratory study carried out in this investigation. It is observed that the liquid limit values are decreased by 57 %, 63% and 70% respectively for 1% of KCl, CaCl2 and FeCl3 chemicals added to the expansive clay. Marginal increase in plastic limits is observed with addition of chemical to the expansive clay. Decrease in plasticity index is recorded with addition of chemical to the expansive soil. The shrinkage limit is increasing with 1.5 % chemical addition; it is observed that the shrinkage limit of stabilized expansive clay is increased from 12% to 15.1%, 15.4% and 16% respectively for KCl, CaCl2 and FeCl3. The D.F.S values are decreased by 40%, 43% and 47% for 1% of KCl, CaCl2 and FeCl3 treatments respectively. The CBR values are also increased by 80%, 103% and 116% respectively for 1% of KCl, CaCl2 and FeCl3 treatment The Significant change in undrained cohesion and marginal change in angle of internal friction is observed with addition of chemicals to the expansive clay. The UCS values are increased by 133%, 171% and 230% respectively for 1% ofkcl, CaCl2 and FeCl3 treatments for a curing period of 14 days. V. SCOPE FOR FURTHER WORK Advanced cyclic Tri axial tests may be conducted for further confirmation of test results. REFERENCES I. A S S Vara Prasad N Avas and S Ashok Kumar (2016), Stabilization of Marine Clay with Sawdust and Lime for II. III. IV. Pavement Subgrades, IJSRD - International Journal for Scientific Research & Development, Vol. 4, Issue 07. Anandakrishnan, M. and Dhaliwal, S.S. (1966): Effect of Various constructions of sodium chloride and Calcium Chloride on the pore pressure parameters and on strength parameters of Black Cotton Soil, Research Report, Dept. of Civil Eng., IIT,Kanpur, India. Bansal, R.K., Pandey, P.K.and Singh, S.K (1996): Improvement of a Typical Clay for Road Subgrades with Hydrated Lime, Proc. of National Conf. on Problematic Subsoil Conditions, Terzaghi-96, Kakinada, India, pp Bell, F.G. (1993): Eng. Treatment of Soils, E&FN Spon Pub. Co. V. Bhattacharya, P. and Bhattacharya, A. (1989): Stabilization of Bed banks of Railway Track by Lime Slurry Pressure Injection Technique, Proc. of IGC-89, Visakhapatnam, Vol. 1, pp. All Rights Reserved 120

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