A Study on Soil Stabilization of Clay Soil Using Flyash

Transcription

1 Volume 1, Issue 2, October-December, 2013, pp , IASTER Online: , Print: ABSTRACT A Study on Soil Stabilization of Clay Soil Using Flyash R. Saravanan*, Roopa Saira Thomas **, Merlin Joseph ** *Assistant Professor, **UG Students Department of Civil Engineering, Vivekanandha College of Technology for Women, Tiruchengode, India, This paper presents the laboratory study of expansive clay soil with fly ash material. The expansive clay soil was collected from near Tiruchengode, Tamilnadu, India. The clay soil behavior was studied in addition of different percentage of fly ash. (0, 10%, 20%, 30% and 40%). The atterberg limits, specific gravity, unconfined compressive strength and Standard Proctor s compaction tests were performed on expansive clay soil. The results are indicated that in addition of fly ash reduces the plasticity index and specific gravity of the expansive clayey soil. The optimum moisture content (OMC) and maximum dry density (MDD) curves indicate that addition of fly ash increases the OMC and maximum dry density of the expansive soil. The strength properties of the expansive clayey soil have increased 21.1%. Based on the Standard Proctor s Compaction test, the Optimum Content of fly ash was found as (10 %). Keywords: Expansive clayey soil, Fly ash, UCS, OMC, MMD. I. INTRODUCTION Clay exhibits generally undesirable engineering properties. They tend to have low shear strength and to lose shear strength further upon wetting or other physical disturbances. They can be plastic and compressible and they expand when wetted and shrink when dried. Fly ash was successfully used for stabilizing expansive clays. Depending upon the soil type, the effective fly ash content for improving the engineering properties of the soil varies between 20 to 25%. Expansive soil has the tendency to swell when they come in contact with moisture and to shrink if moisture is removed from the soil. The volume changes in swelling soils are cause of many problems in structures that come into their contact or constructed out of them. The expansive soils in India have liquid limit values ranging from 50 to 100 %, plasticity index ranging from 20 to 65% and shrinkage limit from 9 to 14%. The comprehensive review of literature shows that a considerable amount of work related to the determination of deformation characteristics and strength characteristics of expansive soil is done worldwide. II. LITERATURE STUDIES Fly ash by itself has little cementations value but in the presence of moisture it reacts chemically and forms cementations compounds and attributes to the improvement of strength and compressibility characteristics of soils. It has a long history of use as an engineering material and has been successfully employed in geotechnical applications. 33

2 Erdal Cokca (2001): Effect of Fly ash on expansive soil was studied by Erdal Cokca, Fly ash consists of often hollow spheres of silicon, aluminum, and iron oxides and unoxidized carbon. There are two major classes of fly ash, Class C and F. The former is produced from anthracite and latter is produced from burning lignite. Both the classes are puzzolans which are defined as siliceous and aluminous materials. Thus expansive soil can be potentially stabilized by cation exchange using fly ash. Specimens with fly ash was cured for 28 days and hence found that plasticity index activity decreased with increasing percentage stabilizer and curing time and optimum content of the fly ash decreases. The change in physical properties causes immediate flocculation of clay particles. Concluded that both high and low calcium fly ash can be recommended as effective stabilizing agents for improvement of the soil. 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 CBR of the 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 upto the first optimum level. Further addition of fly ash beyond the optimum level causes the decrease upto 60% and then upto 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. Phanikumar and Sharma (2004): The ash blended expansive soil with fly ash contents of 0, 5%, 10%, 15% and 20% on a dry weight basis and they inferred that increase in fly ash content reduces plasticity characteristics and free swell index (FSI) was reduced by about 50% by the addition of 20% fly ash. When the fly ash increases there is a decrease in the optimum moisture content and the maximum dry unit weight increases. Hence the expansive soil is rendered more stable. The undrained shear strength of expansive soil blended with fly ash increases with the increase in ash content. III. MATERIALS USED Expansive soil: The expansive soil used in this study which is available in local was collected at the depth of 2m from ground level. The index and engineering properties of expansive soil is determined as per the IS code 2720 (1974). Fly Ash: Class C fly ash was used. Its constituents are listed in the table: 1 Table 1: Properties of Expansive soil Properties Values Initial moisture content 3.1% Liquid limit 53% Plastic limit 29% Plasticity index 24% Shrinkage limit 12% Specific gravity 2.62 Maximum Dry Density (kn/m 3 ) 13.1 Optimum Moisture Content % Unconfined Compressive strength (kn/m 2 ) 180 Soil Classification CH 34

3 Table 2: Properties of Fly Ash Properties Values Liquid limit 84% Plastic limit Non plastic Specific gravity 2.09 Maximum Dry Density (kn/m 3 ) 13.2 Optimum Moisture Content 27% IV. EXPERIMENTAL TESTING PROCEDURE The laboratory studies were carried out on the sample of expansive soil and expansive soil+ Fly ash. The tests were carried out both on natural soil and expansive soil with Fly ash collected from Mettur Thermal Power plant. The clay soil was studied with various percentage of fly ash material. The proportions are 0%, 10%,20%,30% and 40% respectively The fly ash was added with soil sample and mixed thoroughly by hand mixing in the laboratory. The following tests were carried out by using clay soil with fly ash material. Liquid Limit: The Liquid limit test was conducted on expansive soil using Casagrandae s apparatus as per the procedure laid down in IS: 2720 part 4(1970). Plastic limit: The Liquid limit test was conducted on expansive soil as per the procedure laid down in IS: 2720 part 4(1970). Shrinkage limit: The Liquid limit test was also conducted on expansive soil as per the procedure laid down in IS: 2720 part 4(1972). Proctor s standard compaction test: Preparation of soil sample for proctors compaction test was done as per IS: 2720 part 6(1974). This figure 1 shows the optimum moisture content and MDD of the clay soil and clay with fly ash. The MDD increases with increasing fly ash content, and decreases linearly. Corresponding OMC decreases with increasing FA. The OMC and MDD values of 0%, 10%, 20%, 30% and 40% of clay with fly ash are given in table 4. Figure 1 Optimum Moisture Content Versus Maximum Dry Unit Weight Unconfined Compressive strength: The unconfined compressive strength tests was conducted on expansive soil as per IS 2720 part10 (1973). All the samples were prepared by static compaction at OMC and maximum dry density to maintain same initial dry density and water content. After removing impurities the soil was mixed with fly ash in varying proportion by volume. The mixing was thoroughly carried out manually and the tests were conducted as per standard procedures. 35

4 The Liquid limit and plastic limit of the soil with varying percentage pg fly ash is given in Table1. The proctor tests carried out is summarized. Unconfined compression strength tests have been carried out in cylindrical samples of 36 diameter and 72 mm high with compaction apparatus with OMC. These results are given in Table 4. Table 3: Atterberg Limits of Soil Fly Ash Mixtures Sl.No Soil Type Liquid Limit Plastic Limit Plasticity Index 1. Expansive Soil Expansive Soil + 10% FA Expansive Soil + 20% FA Expansive Soil + 30% FA Expansive Soil + 40% FA Non plastic Non plastic NA NA: Not applicable Table 4. Strength Properties of Soil Fly Ash Mixtures Description MDD (kn/m 3) OMC UCS (kn/m 2) Expansive Soil Expansive Soil + 10% FA Expansive Soil + 20% FA Expansive Soil + 30% FA Expansive Soil + 40% FA V. RESULTS AND DISCUSSIONS Effect on Atterberg Limit: Liquid limit and plastic limit of soil mixed with different percentage of Fly ash have been investigated in the laboratory in accordance with IS: 2720 (part 5) Figure 2 indicates that plastic limit value of soil decreases with increasing properties of fly ash. Figure 2 Soil versus Atterberg s Limits Effect on Strength Characteristics: The compaction test has been performed on the expansive soil with fly ash in accordance with IS 2720 (part 8) Figure 3. Soils Versus Maximum Dry Density 36

5 The MDD of the expansive soil with fly ash has increased from 1.3g/cc to 1.531g/cc. Figure 3 Soil versus OMC in % Figure 4 Soil versus UCS Figure 3 shows the decrease of OMC content from % to %. Figure 4 shows that the unconfined compressive strength of the expansive clay with 10% addition of Fly ash has increased to 21% VI. VII. CONCLUSIONS 1. The unconfined compression strength of the given soil sample has increased 21% in addition of the fly ash content. 2. The dry density of the clayey soil sample is increased 15 % of the natural soil sample. 3. The optimum content of the clayey soil sample has decreased 9% of the natural soil sample. 4. The unconfined compression test has increased 21% from the natural soil sample. 5. The optimum content of the fly ash content has found that 10% in addition of the natural soil sample. ACKNOWLEDGEMENTS The authors first of all thank the God Almighty for giving this opportunity to present this paper. We thank our parents for encouraging us for presenting the paper. The authors express their sincere gratitude to Prof. Dr. S. Suresh Kumar, B.E., M.S., M.Tech., Ph.D., Principal, Vivekanandha College of Technology for Women for motivating and giving us this platform. We also thank Prof. K. Poongodi, Head of Civil Department and Prof.R.Saravanan, Assistant Professor, Department of Civil Engineering, Vivekanandha College of Technology for Women who has encouraged us to take all the pain and continuously guided us for the submission of the paper. At last but not the least the authors express their sincere thanks to their colleagues spending their time in helping for the submission of the paper. REFERENCES [1] Gopal Rajan, A.J.R Rao, a textbook on Fundamentals of soil mechanics [2] IS: 2720 (1973): Determination of Strength properties and index properties of soil. [3] Gourly, C.S., Newill,.D Expansive soils. [4] Petry, T.M.; and Little, D.N., Review of Stabilization of clays and Expansive soils in pavement [5] Brooks, R.M.; (2009). Soil stabilization with fly ash and rice husk ash. International Journal of Research and Reviews in applied sciences, Vol 1, issue 3, [6] Dr. K.R. Arora, a textbook on Soil mechanics and foundation engineering. 37