Geotechnical Characteristics of Hubli-Dharwad Black Cotton Soils Mixed with Fly Ash: an Experimental Evaluation

Indian Geotechnical Conference – 2010, GEO trendz December 16–18, 2010 IGS Mumbai Chapter & IIT Bombay

Geotechnical Characteristics of Hubli-Dharwad Black Cotton Soils Mixed With Fly Ash: An Experimental Evaluation

Hakari, Udayashankar D. Faculty e-mail: [email protected] Department of Civil Engineering, S.D.M.College of Engineering & Technology, Dharwad [Formerly Manager( Technical),Karnataka State Financial Corporation, Bangalore]

ABSTRACT The degree and level of soil engineering problems run high and become multifold in case of expansive soils which exhibit the typical character of swelling and shrinkage. The wide spread of the black cotton soil in the twin city of Hubli-Dharwad has posed challenges and problems to the construction activities. A task was therefore undertaken to investigate and improve the engineering properties of the black cotton soils of Hubli-Dharwad so that, a better understanding is facilitated for the civil engineering practitioners, while dealing with these soils. The West Coast Paper Mills, Dandeli (Karwar Dist,Karnataka), located at about 60 km. from Hubli-Dharwad generates huge quantity of fly ash and the fly ash management is posing serious problem. Considering the proximity and availability aspects, the fly ash was chosen to be used for the task, as a stabilizer of black cotton soil. The paper investigates the effect of Dandeli fly ash treatment to the black cotton soils of Hubli-Dharwad on their index, compaction and strength properties in an effort to improve their behaviour.

1. INTRODUCTION characteristics of the black cotton soils under study and Thermal power plants, cement, steel, paper industries all over briefly covers the experimental evaluation carried out in the world contribute enormous quantity of fly ash every year. this regard. Environmentally safe disposal of fly ash has necessitated the 2. MATERIALS AND METHODS exploration of innovative and cost effective methods of utilizing the fly ash in many fields. The major uses of fly ash Black cotton Soil mostly arise out of its pozzolanic property which can be used The investigations contained in this work have been carried for stabilization of soils. Pozzolanic fly ashes can be out on the black cotton soils obtained from Hubli-Dharwad advantageously made use of to improve the geotechnical municipal corporation area, which are tropical black clays properties of black cotton soils (Yudhbir and Honjo,1991). derived from the weathering of meta volcanic rocks. The use of fly ash for stabilistion of soils in road These soils cover more than 50% of the city corporation construction was studied by Amarjit Singh(1967). Uppal and area. The geotechnical properties and chemical Dhawan(1968) reported that fly ash is useful for stabilization composition are given in Table-1 and 2 respectively. The of various Indian soils. Fly ash has been successfully used as values of liquid limit ,plasticity index and shrinkage limit stabilizing agent for different soils by various researchers, Table 1 both in laboratory and also in field. Amos and Wright(1972) Soil property Value Soil Property Value reported the effect of mixing fly ash with clayey and loamy soils on their geo technical properties. The properties of soil Specific gravity 2.68 OMC( %) 26.00 Liquid limit(%) 66.00 are improved by cation exchange, flocculation and 3 pozzolonic cementation (Bell,1988).The addition of fly ash Plastic limit (%) 28.20 MDD(kN/m ) 15.20 Plasticity 37.80 to clayey soils reduced their plasticity and swelling index(%) 16.90 CBR 1.15 characteristics (Shivapullaiah et.al.1996). Shrinkage The paper presents the attempts made in utilizing the limit(%) UCS (kN/m 2) 112.8 Dandeli fly ash for improving the geotechnical 442 D. Hakari Udayashankar

Table 2 Black Cotton Soil Soil Constituent Value Soil Constituent Value Based on the geotechnical properties of the virgin black (%) (%) cotton soils, the degree of expansiveness or swelling potential of these soils is evaluated to be very high ( Holtz Silica (SiO 2) 53.35 Titanium oxide 0.19 Alumina (Al 2O3) 13.24 (TiO 2) and Gibbs 1956,Seed et.al.1962, Dakshanamurthy and Ferric oxide(Fe 2O3) 7.08 Sodium oxide 0.21 Raman 1973 and Chen 1988). Calcium oxide(CaO) 5.81 (Na 2O) The suitability of these soils for their use in Magnesium 2.83 Loss on ignition 16.93 embankment, foundation and roads is assessed based on oxide(MgO) 0.36 the compaction parameters and CBR (IS 1498-1970) as Potassium shown in Tables 4 and 5. oxide(Ka 2O) Table 4 indicate the possession of high degree of expansion and Parameter Liquid Plasticity Shrinkage Degree of high potential for swelling of these soils (Dakshanamurthy Limit Index Limit Expansion et.al.1973, Chen 1988, Holtz and Gibbs 1956 and Seed et.al. 1962). Value >60-70% >35% 10-20% Very high range Fly Ash Study 66% 37.8% 16.90% Very high Dandeli fly ash (DFA) sample is of class-F category and soil sample its properties and composition are given at Table-3.

Black Cotton Soil and DFA Mixes Table 5 The black cotton soil samples were mixed with DFA in Parameter MDD(KN/m 3) OMC(%) CBR Suitability varying percentages of 10%, 20%, 30%,40% and 50%. The Value range 16.0-17.0 20-22 >4 Fair corresponding mixes were designated as M-10, M-20, M-30,M-40 and M-50 respectively. Study soil sample 15.2 26 1.15 Poor

Table 3 DFA property Value DFA Constituent Value Black Cotton Soil and DFA Mixes (%) Table 6 presents the test results showing the variations of Specific gravity 2.07 Silica (SiO 2) 57.00 the geotechnical parameters of the black cotton soil mixed Liquid limit(%) 59.00 Alumina (Al 2O3) 23.00 with different percentages of DFA. Plastic limit Non- Ferric oxide 8.32 Table 6 plastic (Fe 2O3) MIX → M-10 M-20 M-30 M-40 M-50 Plasticity index -- Calcium oxide 2.70 Sp.gravity 2.62 2.53 2.50 2.33 2.22 Shrinkage limit Vary (CaO) Liquid limit (%) 63.0 60.0 57.5 48.0 46.0 with Magnesium oxide 0.83 Plastic limit (%) 28.9 27.2 26.3 24.8 23.1 initial (MgO) Plasticity Index % 34.1 32.8 31.2 23.2 22.9 Shrinkage limit % 17.3 17.5 18.2 29.3 37.0 water Titanium oxide 0.23 MDD (KN/m 3) 15.5 16.8 17.9 16.2 15.3 content (TiO 2) OMC (%) 24.3 24.0 23.2 2.60 21.3 OMC (%) 41.00 Loss on ignition 7.92 C.B.R. 0.77 2.09 2.24 2.64 1.80 MDD (KN/m 3) 11.60 Free lime content 2.86 UCS (KN/m 2) 0 day curing 140.09 163.36 218.03 257.97 291.6 The black cotton soil and DFA were mixed thoroughly 1 day curing 178.67 194.03 252.84 306.54 342.6 on dry weight basis in the said proportions in their fine 7 days curing 238.12 267.82 274.33 347.88 395.7 state. The finely blended mixes were then kept for oven Index Parameters drying for 24 hours and tests were conducted immediately Specific Gravity after wet mixing with distilled water in required quantity depending on the test. For the strength test, curing periods The specific gravity of soil DFA mix decreases with the of 1 and 7 days were considered. increase in the percentage of fly ash. It is found to decrease from 2.62 to 2.22 with the increase in the percentage of fly Test Procedures ash from 10% to 50% respectively (vide fig.1). This is due to The tests for specific gravity, Atterberg limit, compaction the effect of considerable difference in the specific gravity of parameters, California bearing ratio and unconfined compressive strength were conducted as per relevant I.S. DFA (2.07) and that of the black cotton soil under study (2.68). 2.65 codes. M10 2.6 M20 2.55 M30 3. TEST RESULTS AND DISCUSSION 2.5

2.45

The engineering behaviour of soils, the black cotton soils 2.4

2.35 in particular, can be assessed from their plasticity values M40 2.3 as well as from their compaction and strength parameters. SPECIFICGRAVITY 2.25 M50 The effect of addition of DFA without any additives and 2.2 0 10 20 30 40 50 60 the resulting changes in the index, compaction and strength % INCREASE OF FLY ASH parameters of the virgin black cotton soil has been studied. Fig. 1: Variations of Specific Gravity Geotechnical Characteristics of Hubli-Dharwad Black Cotton Soils Mixed With Fly Ash... 443

Liquid limit Shrinkage Limit The variation of liquid limit on addition of fly ash to the As can be seen from fig.5, the addition of fly ash increases black cotton soil is shown in fig. 2. The liquid limit decreases the shrinkage limit of black cotton soil. It increases with with the addition of fly ash, showing a marginal decline up increasing percentages of fly ash. The increase is marginal to 30% of fly ash (M-30 mix) and then after decreasing on addition up to 30% fly ash and is considerable on further considerably for M-40 mix. The primary clay mineral present addition of fly ash. The increase in the shrinkage limit is in the black cotton soil is montmorillonite and as such the mainly due to flocculation of clay particles by free lime liquid limit of these soils is essentially controlled by the present in the fly ash. thickness of diffused double layer and the shearing resistance 40 M50 at particle level. The addition of fly ash results in the decrease 35 M40 of liquid limit due to the effect of reduction in the diffused 30 double layer thickness as well as effect of dilution. The 25 M30 decrease in the liquid limit indicate desirable change with 20 M10 M20 15 the soil fly ash mix gaining shear strength at an earlier stage 10 SHRINKAGELIMIT(%) than the virgin black cotton soil. 5 0 0 10 20 30 40 50 60 70 M10 M20 % INCREASE OF FLY ASH 60 M30 M40 50 M50 Fig. 5: Variations of Shrinkage Limit 40

20 Compaction Parameters LIQUID LIMITLIQUID(%) 10 Optimum Moisture Content (OMC) and Maximum dry 0 0 10 20 30 40 50 60 % INCREASE OF FLY ASH Density (MDD) Fig. 2: Variations of Liquid Limit The compaction characteristics for modified Proctor compactive effort for the black cotton soil- fly ash mixes Plastic Limit reveal that the MDD increases and the OMC decreases with The addition of fly ash shows a steady decline in the plastic increasing fly ash content. However, beyond 20% fly limit as shown in the fig.3. The addition of 10% fly ash ash,only marginal increase in MDD is observed with slightly increases the plastic limit, which is due to continuous decrease in the OMC (vide fig. 6).

flocculation owing to the presence of free lime in the fly ) 3 ash. Further increase in the addition of fly ash results in 30 M10 M20 M30 the decrease of plastic limit. This is because, with increased 25 M40 addition of fly ash, the amount of soil to be flocculated M50 20 decreases and the finer particles of fly ash may be incorporated in the voids of flocculated soil ; thereby 15 MDD 10 decreasing the water held in the pores leading to the OMC decrease in the plastic limit. 5

35 0

30 M10 M20 AND(KN/M M.D.D. (%) O.M.C. 0 10 20 30 40 50 60 M30 25 M40 M50 % INCREASE OF FLY ASH 20 15 Fig. 6: Variations of Max.Dry Density (MDD) and Optimum 10 PLASTIC(%) LIMIT 5 Moisture Content(OMC)

0 0 10 20 30 40 50 60 The behaviour of black cotton soil is controlled by % INCREASE OF FLY ASH diffused double layer. The addition of fly ash in small Fig. 3: Variations of PPlastic Limit percentage results in the decrease of repulsive pressure of Plasticity Index soil particles. This in turn reduces the resistance to Fig. 4 shows the variation of plasticity index with the compactive effort and the mix gets compacted to relatively addition of fly ash. Addition of fly ash decreases the higher densities. Though there will be flocculation due to plasticity index of black cotton soils. The decrease is more free lime of fly ash, this effect is dominated when the fly with increase in the percentages of fly ash, as it can be ash percentage is low. Hence a marginal increase in dry seen that the plasticity index decreases steeply from 31.1% density is observed. Further addition of fly ash beyond 30% for M-30 mix to 23.2% from M-40 mix. results in increased flocculation due to increased availability

40 of free lime content of fly ash. This would increase the M10 35 M20 M30 repulsive forces of soil particles, thereby increasing the 30

25 M40 resistance to compactive effort and hence the density of M50 20 mix starts decreasing. The compaction curve becomes flatter 15

10 with increasing quantity of fly ash. The effect of flocculation PLASTICITYINDEX (%) 5 can be more pronounced in case of class-C fly ashes which 0 0 10 20 30 40 50 60 % INCREASE OF FLY ASH have higher free lime content. Fig.4: Variations of Plasticity Index 444 D. Hakari Udayashankar

California Bearing Ratio (C.B.R.) the corresponding increase in the addition of DFA Fig.7 shows the variation of the soaked CBR values with from 10% to 50% respectively. The shrinkage limit the increasing percentages of fly ash. It is observed that increases from 17.3% to 37% for increasing in the the CBR values show a steady increase up to 2.64 with addition of DFA from 10% to 50% respectively. addition of fly ash up to 40%.Further increase in the fly (iii) In respect of the com paction param eters, the ash percentage results in reduction of CBR value. The m ax im um dry den sity is foun d to increase from 1 5 .5 nature of such variation is based on the same factors briefed 3 3 K N /m for M-10 mix to 17.9 KN/m for M-50 mix in the prepara. ; and further increase in the addition of DFA is

3 observed to decrease it. The optimum moisture M40 M30 2.5 M20 content decreases from 24.3% for M-10 mix to 2 21.3% for M-50 mix. The CBR value increases from M50 1.5 0.77% for M-10 mix to 2.64% for M-50 mix. Any M10 1 RATIO(CBR) further increase in additon of DFA does not increase 0.5

CALIFORNIABEARING CBR value. 0 0 10 20 30 40 50 60 (iv) The unconfined compressive strength of these soils % INCREASE OF FLY ASH increases from 140.9 KN/m 2 for M-10 mix to 291.6 Fig.7 Variation of California Bearing Ratio (CBR) KN/m 2 for M-50 mix, with no curing. For a curing Strength Parameter period of 7 days, the trend of increase in the strength Unconfined Compressive Strength (UCS) is found more pronounced and the unconfined compressive strength increases from 238.52 KN/ The variation of unconfined compressive strength with 2 2 addition of the different percentages of fly ash for 0,1 and m for M-10 mix to 395.7 KN/m for M-50 mix. 7 days curing period is shown in fig.8. It is seen that the (v) The geotechnical properties of Hubli -Dharwad strength increases on addition of small percentage of 10% black cotton soils can be favourably changed with fly ash, but with further increase in fly ash percentage, no the addition of DFA at an optimum quantity of 40- considerable increase in strength is observed. This is due 50%. to the probable disturbance of soil skeleton and consequent REFERENCES reduction in cohesion. The strength of soil is observed to improve considerably with curing which is due to the Amarjit Singh (1967). Use of lime-fly ash in soil stabilisation pozzolanic reactivity of the free lime content of the fly ash. for roads, Jl. Of Indian Roads Congress, vol-XXX-1,143. A mix of fly ash of class-C with increased curing periods Amos,D.F. and Wright,J.D. (1972). The effect of soil fly Ash may be more effective in further improving the strength of on soil physical characteristics, Proc. of Third the black cotton soil. Mineral Waste Utilisation Symposium, Chicago , 95-104. Bell,F.G.(1988). Stabilisation and treatment of clay soils 450 M50 400 with lime- Part-1,Basic Principles. Ground Engineering , ) M40 2 350 21(1), 10-15. M30 7 Days Curing 300 M20 M10 1 Day Curing Chen,F.H.(1988). Foundation on expansive soils , Elsevier 250 0 Days Curing 200 Scientific Publishing Co., Amsterdam. 150 Dakshanmurthy,V.and Raman,V.(1973).A simple method of 100 identifying expansive soil, Soil and Foundations , STRENGTH(KN/M 50 Japanese Society of Soil Mechanics and Foundation 0 UNCONFINEDCOMPRESSIVE 0 10 20 30 40 50 60 Engg., 13(1), 97-104. % INCREASE OF FLY ASH Holtz,W.G. and Gibbs,H.J. (1956). Engineering. properties Fig. 8: Variation of Unconfined Compressive Strength (UCS) of expansive clays,Transactions, ASCE, vol.121,pp.53- 87. 4. CONCLUSIONS Seed, H. B., Woodward, R. J. and Lundgren, R.(1962). The following conclusions are drawn from the present Prediction of swelling properties of compacted clays. Jl. investigation, of Geotech. Engg Divn., Proc. of ASCE, 88, 97-104. (i) The black cotton soils of Hubli -Dharwad have high Shivapullaiah, P.V., Prashanth,J.P., Sridharan,A.(1996). degree of expansion and possess high swelling Effect of fly ash on the index properties of black cotton potential and require stabilization for their better soil, Soils and Foundations , 36, 97-104. performance. Uppal,H.L.and Dhawan,P.K.(1968). A resume on the use of (ii) The index parameters of the study soils improve flyash in soil stabilization, Road Research papers ,No.95 with the addition of DFA. The liquid limit decreases Yudhbir and Honjo,Y.(1991). Applications of Geotechnical from 63% to 46%, plastic limit from 28.9% to 23.1% engineering to environmental control. Theme lecture 5, and the plasticity index from 34.1% to 22.9% ; for 9 ARC, 2, 431-469,Bangkok,Thailand.