Subgrade Characteristics of Locally Available Soil Mixed With Fly Ash and Randomly Distributed Fibers

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1 Subgrade Characteristics of Locally Available Soil Mixed With Fly Ash and Randomly Distributed Fibers Prof. R.K Sharma Abstract Expansive soils cause lots of civil engineering structural damage, particularly to low-rise buildings. These swelling soils typically contain clay minerals that attract and absorb water. Certain inherent properties of these expansive soils need modification for their bulk use in the construction of highways/runway pavements, embankments, etc. This paper presents the results of investigation on the behavior of expansive soil modified with fly ash, and blend of soil, fly ash and Recron 3S fibre of 12mm length. The properties like grain size distribution, moisturedensity relation and CBR are studied for soil blended with fly ash in the range of 20-80%. The mixture of soil with 30% fly ash was selected for further modification with fibre content in the range of %. The properties of moisture-density relation and CBR are evaluated. Keywords Fly Ash, Recron Fibers, MDD, OMC,CBR. W I. INTRODUCTION ITH the rise in thermal power generation, environmental pollution has resulted in massive fly ash generation and the environmentally acceptable disposal of this material has become an increasing concern. Fly ash is waste material imposing hazardous effect on environment and human health. Also, it cannot be disposed of properly and its disposal is not economically viable but if it is blended with other construction materials like clayey soil then it can be used best for various construction purposes like subgrade, foundation base and embankments. Also quality construction materials are not readily available in many locations and are costly to transport over long distances. Hence, over the last few years, environmental and economic issues have stimulated interest in development of alternative materials that can fulfill design specifications. The established techniques of soil / fly ash stabilization by adding cement, lime and reinforcement in form of discrete fibers cause significant modification and improvement in engineering behavior of soils/ fly ash. Fibers are simply added and mixed randomly with soil and fly ash. Studies concerning fly ash and lime utilization for soil stabilization have been conducted in the past by many investigators like Mitchell and Katti (1981), Maher et al Prof. R.K Sharma is at National Institute Of Technology Hamirpur (H.P.), India. (1993), Consoli et al (2001). The physical and chemical mechanisms of both short and long term reactions involved in lime stabilization of the soils or soil fly ash mixtures have been extensively described in literature by Ingles and Metcalf (1972), Brown (1996). Edil et al (2006) indicated the effectiveness of fly ashes for stabilization of fine grained soils. The results of direct shear tests performed on sand specimens by Gray and Ohashi (1983) indicated increased shear strength and ductility, and reduced post peak strength loss due to the inclusion of discrete fibers. The study also indicated that shear strength is directly proportional to fiber area ratio and length of fiber up to certain limit. These results were supported by a number of researchers like Gray and Al-Refeai (1986), Gray and Maher (1989), Al-Refeai (1991), Michaowski and Zhao (1996), Ranjan et al (1996), Michaowski and Cermak (2003)using consolidated drained triaxial tests. Maher and Ho (1994) indicated that increase in strength and toughness of kaolinite fiber composite was a function of fiber length and content, and the water content. It was indicated that the contribution of fibers to peak compressive strength was reduced, and ductility increased, with increasing fiber length. Consoli et al (1998) indicated that inclusion of fiber glass in silty sand effectively improves peak strength. Consoli et al (2002) indicated that due to inclusion of polyethylene terephthalate fiber in fine sand improves both peak and ultimate strength which is dependent on fiber content. Kumar and Tabor (2003) studied the strength behavior of silty clay with nylon fiber for varying degree of compaction. The effect of polymer fiber inclusion on plain fly ash was studied by Chakraborty and Dasgupta (1996) by conducting triaxial tests. The fiber content ranging from 0 to 4 % by weight of fly ash was used with constant fiber aspect ratio of 30. The study indicates increase in friction angle. The study on soil fly ash mixture reinforced with 1% polyester fibers (20 mm length) was conducted by Kaniraj and Havanagi (2001), which indicated the combined effect of fly ash and fiber on soil. Kaniraj and Gayatri (2003) indicated that 1% polyester fibers (6 mm length) increased strength of raw fly ash and change their brittle failure into ductile. Dhariwal(2003) carried out performance studies on California bearing ratio of fly ash reinforced with jute and non-woven geo fibers. This paper summarizes the laboratories studies conducted on soil modified with fly ash and Recron 3S fiber. In this 177

2 investigation, an attempt is made to study how fly ash and fibers may be effectively utilized in combination with the soil to get an improved soil material which may be used in various soil structures. Fly ash is obtained from Ambuja cement plant at Darlaghat (H.P). Locally available soil has been used in this experimental investigation. Various technical properties like specific gravity, particle size distribution, liquid limit and plastic limit, compaction characteristics of the material have been investigated individually as well as in different combinations. CBR characteristics of the most appropriate combinations of the three materials used have been studied at the optimum moisture content and maximum dry densities. The variation of the MDD versus percentage of fly ash, MDD versus percentage of fibre content, OMC versus percentage of fly ash, OMC versus percentage of fibre content, CBR versus percentage of fly ash and CBR versus percentage of fibre content was studied. The results have been shownforthe most appropriate combination of materials consisting ofsoil, fly ash and fibres. II. SCOPE AND OBJECTIVES In the present study, an attempt is made to study how fly ash and Recron fibers may be effectively utilized in combination with locally available soils to get an improved quality of composite material which may be used in various soil structures. The soil used in investigation was obtained from NIT Hamirpur (Near Gate 1) and fly ash was obtained from Ambuja cement plant at Darlaghat Himachal Pradesh. Following are the objectives of the present work: Soil and fly ash were mixed in varying percentages and optimized for maximum dry density. The CBR value of the most appropriate combination of the soil and fly ash with varying percentage of Recron fibers has been studied at the optimum moisture content and maximum dry density. III. ENGINEERING PROPERTIES OF MATERIALS USED The soil used in the study was locally available soil and fly ash obtained from Ambuja cement plant. According to IS soil classification system, the soil was classified as sandy clay (SC) and fly ash was classified as poorly graded sand (SP). TABLE I BASIC PROPERTIES OF SOIL AND FLY ASH Particulars of test Soil FA Specific Gravity Coefficientof uniformity (Cu) Coefficient of curvature (Cc) IS soil classification SC SP Liquid Limit 27 % 49.8 % Plastic Limit 13.3 % - Max. Dry Density (g/cc) Optimum Moisture Content % CBR % Fig. 1. Particle size distribution of Soil, Fly Ash & 70% Soil + 30% Fly Ash A. Method of Testing The laboratory studies were carried out in two phases 1. Modification of soil with fly ash by varying percentage of 20%,30%,40%,60% and 80%. 2. Modification of soil with 30%fly ash and varying fibre content in the range of % with an increment of 0.5%. The blending operation was carried out manually and care was taken for uniform mixing. Laboratory tests are carried out in accordance with the specification of relevant Indian Standards. In the first phase, the properties like moisture-density relation (IS light compaction) and CBR are evaluated for the soil blended with varying percentage of fly ash. In the second phase of investigation, the effect of fibre content on the properties like moisture-density relation (IS light compaction) and CBR (soaked and un-soaked) are evaluated for the soil blended with 30% of fly ash. IV. RESULTS AND DISCUSSION A. Compaction Characteristics IS Light compaction tests were carried out on different proportions of fly ash and soil in accordance with the procedure laid in IS:2720 (Part VII) 1980/87 so as to study their moisture density relationship. IS:2720 recommends that a mould of 1000 ml capacity having an internal diameter of 100 mm and an internal effective height of mm should be used. The rammer has a mass of 2.6 Kg with a drop of

3 mm. In this test sample is compacted at various water contents in three layers. Each layer is given 25 blows. Fig. 3 shows the variation in the maximum dry density (MDD) and corresponding optimum moisture Ccntent (OMC) for different percentages of fly ash. The MDD value increased initially and then it started decreasing. The MDD was found maximum for 70% soil and 30% fly ash proportion. The MDD value is affected by grain size distribution factor. It is evident from the grain size distribution that increase in fly ash content up to 30% in soil results into a well graded mixture and it results in increase in density of soil blend. The value of OMC increases with increase in fly ash content.with the addition of fibre content in the blend of soil with 30% fly ash, the MDD value initially increased and then it went on decreasing. The value of OMC initially decreased then it went on increasing. Increase in the MDD value might be because of the reason that when fibre was added it occupied the void spaces present in soil fly ash mixture. When fibre content was increased beyond the optimum value the MDD value got decreased. The fibre crosssection is circular and surface area is more so when fibre content is increased beyond the optimum value more void spaces were created resulting decrease in value of MDD. For 0.5% fibre content in the blend of soil with 30% fly ash, the MDD value was found maximum. Fig. 3 shows the variation in MDD and OMC with fibre content. Fig. 3. Variation of MDD and OMC with fibre content B. Strength Characteristics California Bearing Ratio tests (CBR) were carried out on soil mixed with different proportion of fly ash so as to study their bearing capacity. The CBRvalues for different compositions were obtained by compacting the mixture to a MDD and OMC corresponding to IS light compaction and testing in un-soaked conditions.fig.4 shows the variation of CBR values with increased percentage of fly ash in soil.cbr value initially increased with increase in fly ash content and then it started decreasing. The maximum CBR value was found for 70% Soil and 30% fly ash. With the addition of fibre in the blend of soil with 30% fly ash, the CBR (both soaked and un-soaked) value initially increased then it started decreasing. The maximum CBR value (both soaked and unsoaked) was found to be for fibre content of 0.5% in the blend of soil with 30% fly ash. The variation in CBR (both soaked and unsoaked) value with fibre content is shown in fig. 5. Fig. 2. Variation of MDD and OMC with fly ash content 179

4 Fig. 4 Variation of CBR with fly ash content in soil conclusions can be drawn: 1. The poorly graded soil gradually become well graded soil by addition of fly ash. The coefficient of uniformity (C u ) and coefficient of curvature (C c ) of soil gradually reduced from 25.7 to 20 and 5.73 to 2.9 respectively due to replacement by 30 % fly ash. 2. On addition of increasing content of fly ash in soil, MDD of mixtures initially increases then it starts decreasing and OMC of soil increases on addition of increasing content of fly ash in it. The maximum dry density was found to be for 70% soil and 30% fly ash proportion and its OMC was 15%. 3. On addition of increasing content of fly ash in soil CBR value of mixtures initially increases then it starts decreasing. The maximum CBR value was found to be for 70% soil and 30% fly ash proportion. 4. Based upon the study it was concluded that proportion of 70% soil and 30% fly ash is the best proportion having maximum dry density and maximum CBR value. 5. The inclusion of fibres had a significant influence on the engineering behavior of soil-fly ash mixture. There is optimum percentage of fibre content that increases the MDD of soil-fly ash mixture. Different percentage fiber content was added in the proportion of 70% soil and 30% fly ash mixture and it was found that the value of CBR first increases then it decreases with increase in fibre content. The maximum value of CBR was found to be 13.2 % for 0.5 % fibre content. 6. Based upon the study it was concluded that proportion of 70% soil + 30% fly ash fibre is the is the best combination of soil,fly ash and fibre content having maximum CBR value. Hence this proportion may be used in road embankments Fig. 5 Variation of CBR with Fibre content V. CONCLUSIONS Fly ash is a waste material imposing hazardous effect on environment and human health. Also, it cannot be disposed of properly and its disposal is not economically viable but if it is blended with other construction materials like clayey soil then it can be used best for various construction purposes like sub grade, foundation base and embankments. The present study is aimed at improving the properties of soil to suitable for road construction. Based upon the above study following REFERENCES [1] Al- Refeai, T.O (1991) Behavior of granular soil reinforced with discrete randomly oriented inclusions. Geotextile and Geomembranes, [2] Brown, R.W. (1996) Practical foundation engineering handbook. Mc- Graw Hill, New York. [3] Consoli, N.C., Prietto, P.D.M. and Pasa, G.S. (2002) Engineering behavior of a sand reinforced with plastic waste. Journal of Geotechnical and Geoenvironmental Engg., ASCE 128(6), [4] Consoli, N.C., Prietto, P.D.M., Carraro, J.A.H. and Heinech (2001) Behavior of compacted soil-fly ash- carbide lime mixtures. Journal of Geotechnical and Geoenviromental Engineering ASCE 127(9), [5] Consoli, N.C., Prietto, P.D.M. and Ulbrich, L.A (1998) Influence of fiber and cement addition on the behavior of sandy soil. Journal of Geotechnical and Geoenvironmental Engg., ASCE 124(12), [6] Chakraborty, T.K., and S.P. Dasgupta (1996) Randomly reinforced fly ash foundation material. Indian Geotechnical Conference. Volume 1 Madras. India pp Vol. 13, Bund. C 11 [7] Dhariwal, Ashok (2003) Performance studies on California bearing ratio values of fly ash reinforced with jute and non woven geo fibers. National seminar on advances in construction materials 2003 pp

5 [8] Edil, T.B., H.A. Acosta, and C.H. Benson (2006) Stabilizing soft fine grained soils with fly ash. Journal of Materials in Civil Engineering, ASCE 18(2), [9] Gray, D.H. and M.H. Maher (1989) Admixture stabilization of sand with discrete randomly distributed fibers. Proceedings of XII International Conference on Soil Mechanics and Foundation Engineering, Rio de Janeiro, Brazil. Volume 2, [10] Gray, D.H. and T. Al-Refeai (1986) Behavior of fabric versus fiber reinforced sand. Journal of Geotechnical Engineering, 112(8), [11] Gray, D.H. and H. Ohashi (1983) Mechanics of fiber reinforcement in sand. Journal of Geotechnical Engineering, 109(3), [12] Ingles, O.G., and J.B. Metcalf (1972) Soil stabilization principles and practice, Butterworth, Sydney, Australia. [13] Kumar, S. and E. Tabor (2003) Strength characteristics of silty clay reinforced with randomly oriented nylon fibers. Electronic Journal of Geotechnical Engineering (EJGE). [14] Kaniraj, S.R. and V. Gayatri (2003) Geotechnical behavior of Fly Ash mixed with randomly oriented fiber inclusions. Geotextile and Geomembrane , [15] Kaniraj, S. R., and V. G. Havanagi (2001) Behavior of cement stabilized fiber reinforced fly ash soil mixtures. Journal of Geotechnical and Geoenvironmental Engineering, 127(7), [16] Michalowski, R. L. and J. Cermak (2003) Triaxial Compression of sand reinforced with fibers. Journal of Geotechnical and Geoenvironmental Engineering, 129(2) [17] Michalowski, R. L. and A. Zhao (1996) Failure of fiber reinforced granular soils. Journal of Geotechnical Engineering, ASCE 122 (3), [18] Maher M. H. and Y.C. Ho (1994) Mechanical Properties of Kaolinite /Fiber soil composite. Journal of Geotechnical Engineering, ASCE 120(8), [19] Maher, M.H., J.M. Butziger, D.L. DiSalvo, and I.S. Oweis (1993) Lime sludge amended fly ash for utilization as an engineering material. Fly Ash for soil improvement, Geotech. Special Publication No.36, ASCE, New York, [20] Mitchell, J.K. and R.K. Katti (1981) Soil improvement.state-of-the-art report. Proc., 10th Int. Conf. on Soil Mechanics and Foundation Engineering. International Society of Soil Mechanics and Foundation Engineering, London, [21] Ranjan, G., R.M. Vasan, and H.D. Charan (1996) Probabilistic Analysis of Randomly Distributed Fiber Reinforced Soil. Journal of Geotechnical Engineering, ASCE 122 (6),