EVALUATION STUDIES OF EXPANSIVE SOIL TREATED WITH ELECTROLYTES

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1 EVALUATION STUDIES OF EXPANSIVE SOIL TREATED WITH ELECTROLYTES KESAVA N K CHAITANYA G P.G Student Department of Civil Engineering University College of Engineering KAKINADA-5333::INDIA. Dr. G. V.R. PRASADA RAJU Professor Dr. K. RAMU Associate Professor ABSTRACT Expansive soils, such as black cotton soils, are basically susceptible to detrimental volumetric changes, with changes in moisture. This behavior of soil is attributed to the presence of mineral montmorillonite, which has an expanding lattice. In the present work, experimentation is carried-out to investigate the influence of strong electrolyte viz. potassium chloride, calcium chloride and ferric chloride on the properties of expansive soil. A methodical process, involving experimentation in the laboratory under controlled conditions is done. It is observed form the laboratory studies that maximum improvement in the properties of Expansive soil is for treatment compared to other electrolytes tried in this investigation. KEY WORDS: Expansive soils; ; ; 1.1 1NTRODUCTION Expansive soil cover large tracts of several world nations and in India; these deposits are known by the name, black cotton soils which occupy about 2% of its surface area. In India, these soils are predominant in the states of Gujarat, Maharashtra, Madhya Pradesh, Andhra Pradesh, Karnataka and Tamilnadu. After recognizing the problems posed by these soils to civil engineering structures, Engineers from all parts of the world have been trying to find solutions. Among several techniques adopted to overcome the problems posed by expansive soils, lime stabilization gained prominence during the past few decades due to its abundance and adaptability (Snethan et al, 1979). However, it is reported (Chen, 1988) that lime stabilization suffers from the major drawback of difficulty in soil pulverization and mixing of with it. Recent studies (Ramana Murthy, 1998; Srinivas,(28), D. Koteswararao, (211)). indicated that CaCl 2 could be an effective alternative to conventional lime used due to its ready dissolvability in water and to supply adequate calcium ions for exchange reactions. Katti et al (1966) made an attempt to stabilize the in-situ soil using KOH solution and they revealed that it is possible to alter the properties of black cotton soils in place by treating them with aqueous solution of KOH. Frydman et al (1977) studied the use of to modify heavy clay in the laboratory and revealed that from engineering point of view, the use of as a stabilizer appears potentially promising in locations where it is readily and cheaply available. In the present work, the efficiency of (), (CaCl 2 ) and (FeCl 3 ), as stabilizing agents, was extensively studied in the laboratory for improving the properties of expansive soil. ISSN : Vol. 3 No.12 December

2 1.2 OBJECTIV E The objective of the present work is to study the impact of the electrolytes like, CaCl 2 and FeCl 3 on the properties of expansive soil with laboratory. 1.3 MATERIALS USED The details of the various materials and chemicals used in the laboratory experimentation are reported in the following sections Soil The black cotton soil collected from Kothapeta near Amalapuram, in East Godavari District, Andhra Pradesh State, India. The properties of soil are presented in the table. All the tests carried on the soil are as per IS specifications. Table.1. Properties of Expansive soil S.No Property Value 1. Grain size distribution Sand (%) Silt (%) Clay (%) Atterberg limits Liquid limit (%) Plastic limit (%) Plasticity index (%) Shrinkage limit (%) 3. Compaction properties Optimum Moisture Content, O.M.C. (%) Maximum Dry Density, M.D.D (g/cc) Specific Gravity (G) IS Classification CH 6. Soaked C.B.R (%) 2 7. Differential free swell 11 (%) 8 Permeability (cm/sec) ⁷ 9 Shear Strength Parameters Cohesion (C) (Kg/cm²) Angle of internal friction (ø).46 2º Chemicals Used Commercial grade, CaCl 2 and FeCl 3 was used in this study. The quantity of Chemicals was varied from to 1.5% by dry weight of soil. 1.4 LABORATORY EXPERIMENTATION Index Properties ISSN : Vol. 3 No.12 December

3 Different percentages of chemicals (ranging from -1.5% by weight) were mixed with soil (for all the combinations as listed in the table) and the liquid limit, plastic limit and shrinkage limit were determined as per IS:272 (part-5)-1985; IS:272 (part-6) Compaction Properties Optimum moisture content and maximum dry density of the black cotton soil were determined according to the IS Heavy weight compaction test (IS:272 part-8,1983) Differential Free Swell (DFS) The DFS values for all the combinations listed in table and also of the untreated soil, were determined as per IS:272-part XL Strength Tests Tri-axial test, California bearing ratio and Unconfined compressive strength were found for all the soil combinations, as presented. 1.5 LABORATORY TEST RESULTS ON CHEMICAL STABILIZATION In the laboratory, index tests and strength tests were conducted by using different percentages of chemicals with a view to determine the optimum percentage of chemical. The effect of addition of different chemicals to the expansive soil on the Atterberg limits, differential free swell and strength properties are discussed in detail in the following sections.. Table.2. Effect of strong electrolytes on Index Properties of expansive soil Chemical CaCl 2 FeCl 3 Index properties Percentages of chemical WL P.L. I P S.L (%) (%) (%) (%) ISSN : Vol. 3 No.12 December

4 1 8 Liquid Limit (%) Fig.1.Effect of chemicals on liquid limit Plastic Limit (%) Fig.2.Variation of Plastic limit Plasticity Index (%) Fig.3.Variation of plasticity Index ISSN : Vol. 3 No.12 December

5 2 Shrinkage Limit (%) Fig.4.Variation of Shrinkage Limit Effect of Additives on Atterberg Limits The decrease in the liquid limit values for different percentages of chemicals added to the expansive soil is presented in the Table.2. The decrease in the values of liquid limit upto 1% of chemical is significant for all the chemicals, as shown in Fig.1. Beyond 1% there is a nominal decrease in the liquid limit values, for all the chemicals, tried in this investigation. For FeCl 3 treatment there is maximum decrease in the values of the liquid limit when compared with other two chemicals viz. and CaCl 2. There is a nominal increase in the values of the plastic limit with the increase in the percentage of the chemical. The increase in the plastic limit values and the reduction in the liquid limit values cause a net reduction in the values of plasticity index. For 1% chemical, it is observed that, the reduction in plasticity index values are of the order of 35%, 45% and 68% for, CaCl 2 and FeCl 3 treatment respectively with respect to the untreated soil. The effect of, CaCl 2 and FeCl 3 treatments on plasticity index of expansive clay as observed in the laboratory testing are shown in Tables.2. and Fig 3. It can be seen from the figure that, the FeCl 3 treatment has effectively controlled the plasticity index compared to other additives. The shrinkage limit values are increased by 13%, 18% & 22% respectively for 1%, CaCl 2 and FeCl 3 treatments. The reduction in plasticity index, with FeCl 3 treatment could be attributed to the depressed double layer thickness due to cation exchange by trivalent Ferric ions and increased electrolyte concentration, as the chemical is completely soluble in water chemical % chemical D F S (%) CaCl₂ FeCl₃ Table 3: Effect of Chemical on DFS ISSN : Vol. 3 No.12 December

6 DFS (%) Fig 5. Variation of DFS Effect of Additives on DFS The variation of D.F.S. for different percentages of the chemicals is shown in the Table.3& Fig 5. There is a significant decrease in D.F.S. values upto 1% of the chemical, after that the change is marginal. The reduction in the values of D.F.S. at 1% chemical are at the order of 32%, 37% and 5% for, CaCl 2 and FeCl 3 treatments respectively in comparison with untreated soil. The reduction in DFS values could be supported by the fact that the double layer thickness is suppressed by cation exchange with trivalent ferric ions and increased electrolyte concentration.. Table 4: Effect of Chemical on CBR chemical % chemical CBR(soaked) CaCl₂ FeCl₃ CBR (%) 2 1 Fig 6. Variation of CBR ISSN : Vol. 3 No.12 December

7 1.5.3 Effect of Additives on CBR The CBR values are increased by 98%, 125%, 15% when treated with 1%, 1%CaCl 2 &1% FeCl 3 as shown in Table 4 & Fig.6. The increase in the strength with addition of chemicals may be attributed to the cation exchange of, CaCl 2 & FeCl 3 between mineral layers and due to the formation of silicate gel. The reduction in strength beyond 1% each of, CaCl 2 & FeCl 3 may be due to the absorbtion of more moisture at higher, CaCl 2 & FeCl 3 contents. Table 5: Effect of Chemical on shear strength parameters chemical (%) chemical Shear strength Parameters (c, ø) in Kg/cm² & degrees CaCl₂ FeCl₃ 1 day 7 days 14days.46, ,6 1.2,5 1.12, ,4 1.12,5 1.24, ,7 1.8,4 1.19,5.46, ,5 1.5,4 1.16, ,3 1.22,4 1.28, ,2 1.13,3 1.26,4.46, ,4 1.11,4 1.2, ,3 1.26,4 1.36, ,4 1.19,3 1.29, Effect of Additives on Shear Parameters The significant improvement of shear parameters was observed, when treated with 1%, 1%CaCl 2, and 1% FeCl 3 respectively as shown in Table 5. Table 6: Effect of Chemical on UCS chemical (%) chemical Unconfined Compressive Strength(KPa) CaCl₂ FeCl₃ 1 day 7 days 14days ISSN : Vol. 3 No.12 December

8 UCS KPa Fig 7. Variation of UCS in 14 days curing Period Effect of Additives on UCS The UCS values are increased by 147%, 189% and 252% when treated with, CaCl 2 and FeCl 3. The increase in the strength with addition of chemicals may be attributed to the cation exchange of, CaCl 2 and FeCl 3 between mineral layers and due to the formation of silicate gel. The reduction in strength beyond 1% each of, CaCl 2 and FeCl 3, may be due to the absorbtion of more moisture at higher, CaCl 2 & FeCl 3 contents. The optimum percentage of different additives observed during the laboratory experimentation are summarized and presented in the following Table. Additives CaCl 2 FeCl 3 Optimum percentage CONCLUSIONS The following conclusions are made based on the laboratory experiments carried out in this investigation. 1. From the laboratory studies, it is observed that the liquid limit values are decreased by 18%, 23% and 33% respectively for 1% of, CaCl 2 and FeCl 3. There is a decrease in the values of plasticity index with respective chemical treatment because of the decrease in liquid limit and increase in the plastic limit values. Plasticity index is decreased by 35%, 48% and 68% respectively for 1% of, CaCl 2, FeCl The Shrinkage Limit values are increased by 13%, 18% & 22% respectively for 1%, CaCl 2 and FeCl 3 treatments. 3. The Differential free swell values are decreased by 32%, 37% and 5% for 1%, 1% CaCl 2, 1% FeCl 3 respectively with respect to the untreated soil. 4. There is a significant improvement in plasticity and DFS upto 1% chemical, after that the change is marginal. 5. The CBR values are increased by 98%, 125% & 15% respectively for 1%, CaCl 2 and FeCl 3 treatments. 6. The significant improvement of shear parameters was observed, when treated with 1%, 1%CaCl 2, and 1% FeCl 3 respectively 7. The UCS values, are increased by 147%, 189% and 252% respectively for 1%, CaCl 2 and FeCl 3 treatments, for a curing period of 14 days. ISSN : Vol. 3 No.12 December

9 8. It is observed that, the UCS values are increased for all the three chemicals up to 1% and later the strength decrease in trend is observed. REFERENCES [1] Snethen, D.R. et al. (1979), An evaluation methodology for prediction and minimization of detrimental volume change of expansive soils in highway subgrades, research report, Vol. 1, prepared for federal highway administration, Washington. [2] Sivanna,G.S. et al. (1976). Strength and consolidation characteristics of black cotton soil with chemical additives CaCl 2 & KOH, report prepared by Karnataka Engg. Research station, Krsihnarajasagar,India.. [3] Katti, R.K., Kulkarni, K.R. and Radhakrishnan, N. (1966), Research on Black Cotton Soils without and with Inorganic Additives, IRC, Road Research Bulletin, No. 1, pp [4] Holtz, W.G. (1959). Expansive Clays Properties and Problems, First Annual Soil Mechanics Conf., Colorado School of Mines, Colorado, pp [5] Frydman, S., Ravins, L and Ehrenreich, T. (1997), Stabilization of Heavy Clay with, Journal of Geo technical Engg., Southeast Asian Society of Soil Engg., Vol 8, pp [6] Chandrasekhar, B.P., Prasad Raju, G.V.R., Ramana Murthy, V. and Hari Krishna, P. (1999). Relative Performance of Lime and on properties of Expansive soil for pavement subgrades, Proc. Of IGC-99, Calcutta, pp [7] Koteswara Rao.D(211), Laboratory investigations on GBFS- CH soil mixes for the utilization of foundation beds, CONCEPTS- 211, JNT university college of engineering, Kakinada. [8] M. Srinivas(28), Test track studies on chemically stabilized expansive soil subgrades, a Ph.D. thesis, JNT University college of engineering, Kakinada, June 28. ISSN : Vol. 3 No.12 December