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Full Paper Proc. of Int. Conf. on Recent Trends in Transportation, Environmental and Civil Engineering 2011

Consolidation Characteristics of Fly Ash and Lime Treated Black Cotton Soil Vijayakumar Sureban1

1 Alva’s Institute of Engineering and Technology/Department of Civil Engineering, Moodbidri, India Email: v_sureban@rediffmail.com Abstract— With increasing land demand it is unavoidable to carry out constructions in soils such as black cotton soils, which are problematic. Admixture stabilization of such soils is effective, economical and environmental friendly. Using fly ash and lime for improving the consolidation characteristics of the Bagalkot black cotton soil is presented in this paper. With addition of fly ash and lime the consolidation characteristics improved.

A. Effect of Fly Ash and Lime on Coefficient of Consolidation (Cv) The values of Cv at 50 % and 90 % consolidation, for the consolidation pressure range of 4.0 to 8.0 kg/cm2, are calculated by log t and methods respectively. Table II shows the variation of coefficient of consolidation of treated expansive soil with fly ash and lime and the same are presented in Fig.1 and Fig.2 respectively.

Index Terms—black cotton soil, coefficient of consolidation, compression index, consolidation settlement, fly ash, lime , preconsolidation pressure.

TABLE II COEFFICIENT OF CONSOLIDATION OF FLY ASH AND LIME TREATED SOIL

I. MATERIALS AND METHODS Black cotton soil from Bevinamatti village of Bagalkot, Karnataka, has been procured at a depth of 1 m below the ground level by open excavation method. Class “F” fly ash from Raichur Thermal Power Station, Karnataka, having 1.7% free lime was used. The index and engineering properties of soil and fly ash are given in Table I. Commercially available 97% pure lime (CaO) was used. The test program for the study consisted of varying fly ash content from 0-50% and lime from 0-12% by dry weight of soil. All the test procedures employed are as per IS codes. TABLE I GEOTECHNICAL PROPERTIES OF SOIL AND FLY ASH

II. REULTS AND DISCUSSIONS

Figure 1. Variation of coefficient of consolidation with fly ash

The compressibility characteristics of the soil; coefficient of consolidation (Cv) which explains the time rate of consolidation, compression index (Cc) that explains the amount of consolidation, preconsolidation pressure (pc) that explain s the consolidation status of soi l and consolidation settlement (Sc) were studied by the one dimensional consolidation test. © 2011 ACEE DOI: 02.TECE.2011.01.3

Full Paper Proc. of Int. Conf. on Recent Trends in Transportation, Environmental and Civil Engineering 2011

Figure 2. Variation of coefficient of consolidation with lime

Figure 4. Variation of time of consolidation with lime

This means that the consolidation and settlement of the soil treated with fly ash and lime will be sooner than the untreated one.

The increase in the sand fraction caused significant reduction in the compressibility characteristics [1] and [2]. This is attributed to the reason that, with increase in fly ash content the soil became granular showing increased hydraulic conductivity and hence increased rate of consolidation [3]. So, the Cv values of treated soil increased by adding of fly ash and lime. The rate of consolidation can even be studied by the time of consolidation (t). Table III shows the variation of time required for 50% and 90% consolidation of soil treated with fly ash and lime and the same are presented in Fig. 3 and Fig. 4 respectively. TABLE III TIME OF CONSOLIDATION OF FLY ASH TREATED SOIL

B. Effect of Fly Ash and Lime on Compression Index (Cc) and Consolidation Settlement (Sc) The variation of compression index and settlement of soil treated with fly ash and lime are given in Tables IV and V and in Fig. 5 and Fig. 6 respectively. Cosnolidation settlement (Sc) is calculated by “(1)”.

Where, Cc= Compression index e0= Initial void ratio H= Thickness of the sample (mm) p0= Initial pressure (kPa) = Pressure increment (kPa) The Cc value of untreated soil was 0.661. It decreased to 0.236 with fly ash content up to 50 %. Also, with the addition of lime up to 12 % it decreased to 0.066. The Sc of untreated soil was 0.992 mm and with addition of fly ash up to 50 % the Sc reduced to 0.442 mm. With the addition of lime up to 12 % the Sc reduced to 0.109 mm. This is due to the formation of inter particle cementation bonds that improved the strength and reduced the compressibility. This indicates the increased tendency of clay-fly ash blend and lime treated soil to resist the compression and expansion [1] and [4]. The reduction in compressibility characteristics is by a g gregation formation of soil treated with fly ash which resulted in stronger particle aggregates and gave higher resistance to compression [3]. Hence, soil treated with fly ash and lime has low consolidation settlement.

AND LIME

TABLE IV COMPRESSION INDEX AND SETTLEMENT OF FLY ASH TREATED SOIL

TABLE V COMPRESSION INDEX AND SETTLEMENT OF LIME TREATED SOIL

Figure 3. Variation of time of consolidation with fly ash

Full Paper Proc. of Int. Conf. on Recent Trends in Transportation, Environmental and Civil Engineering 2011

Figure 7. Variation of preconsolidation pressure with fly ash Figure 5. Variation of compression index and settlement with fly ash

Figure 8. Variation of preconsolidation pressure with lime Figure 6. Variation of compression index and settlement with lime

It can be seen from Table VII and Fig. 7 and 8 that the addition of fly ash and lime increased the preconsolidation pressure. The preconsolidation pressure of untreated soil was 35 kPa. When fly ash content was varied up to 50 % the preconsolidation pressure increased to 150 kPa and when lime was added up to 12 % the preconsolidation pressure increased to 100 kPa. This is due to the flocculation and cementitious phenomenal effects by the pozzolanic reactions of lime and also by the free lime present in the fly ash that forms the secondary minerals [6] and [7]. Because of the formation of inter particle cementation bonds that improved the strength by aggregation formation of soils treated with fly ash resulting in stronger particle aggregates and higher resistance to compression and hence soil became the over consolidated [1] and [3]. Hence, if soil becomes over consolidated it resists higher structural loads, reducing the compressibility characteristics. The soil subjected to higher preconsolidation pressures has smaller consolidation settlements. Hence, by the addition of fly ash and lime the consolidation settlement can be reduced.

Table VI correlates the degree of compressibility with Cc of soil [5]. TABLE VI DEGREE OF COMPRESSIBILITY OF SOIL

The untreated soil was very highly compressible as its Cc was 0.66. When it was treated with 50% fly ash its degree of compressibility reduced to highly compressible as Cc reduced to 0.24 and when treated with 12% lime it became slightly compressible as Cc became 0.07. C. Effect of Fly Ash and Lime on Preconsolidation Pressure Table VII and Fig.7 and 8 show the variation of preconsolidation pressure (pc) of treated soil with fly ash and lime respectively.

CONCLUSIONS Based on the experimental results the following conclusions can be drawn. With the addition of fly ash from 0 to50% and lime from 0 to12% • Coefficient consolidation increased, which means the faster consolidation process. • Compression index reduced, which means soil became less compressible. • Consolidation settlement decreased. • Preconsolidation pressure increased, which means soil became over consolidated.

TABLE VII PRECONSOLIDATION PRESSURE OF FLY ASH AND LIME TREATED SOIL

Full Paper Proc. of Int. Conf. on Recent Trends in Transportation, Environmental and Civil Engineering 2011 SCOPE FOR FURTHER STUDIES

[3] B.V.Ranganatham, “Basic studies on montmorillonite with soil admixture”, 6th International Conference on Expansive Soil, India, 1-4 December, 1987, p. 31–37. [4] Sudhakar.M.Rao and P.Shivanandan, “Compressibility behaviour of lime-stabilized clay”, Geotechnical and Geological Engineering, vol. 23, 2005, pp. 309–319. [5] Donald.P.Coduto, Foundation Design, Prentice Hall: New Jersey, 1994. [6] A.S.Balasubramanian, D.T.Bergado, B.R.Buensuceso and W.C.Yang, “Strength and deformation characteristics of lime treated soft clays”, Geotechnical Engineering, vol. 20, 1989, pp. 49–65. [7] Jacques Locat, Helene Tremblay and Serge Lerueil “Mechanical and hydraulic behavior of a soft inorganic clay treated with lime”, Can. Geotech. J, vol. 33, 1996, pp.654–669.

The effect of different pore fluids and their chemistry; pH and concentration on compressibility of soil can be studied. The effect of industrial wastes and contaminants on compr essibility character istics of soil ca n al so be investigated. Also, the results of laboratory tests can be taken to the field applications. REFERENCES [1] A.Sridharan and Venkatappa.G.Rao, “Mechanisms controlling volume change of saturated clays and role of effective stress concept”, Geotechnique, vol. 23(3), 2000, pp.359–382. [2] Gholamreza Mesri and Roy E.Olson, “Consolidation characteristics of montmorillonite”, Geotechnique, vol. 4, 1971, pp. 341–352.