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 Plasticity Index % 34.1 32.8 31.2 23.2 22.9 initial (MgO) 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.