Experimental Studies on Clay, Bentonite and Leachate Mixer as Liner Material

Transcription

1 Experimental Studies on Clay, Bentonite and Leachate Mixer as Liner Material V.Giridhar 1, P. Suresh Praveen Kumar 2 and M.C Venkatasubbaiah 3 1. Associate Professor, Department of Civil Engineering, KSRM College of Engineering, Kadapa. (A.P), India 2. Assistant Professor, Department of Civil Engineering, KSRM College of Engineering, Kadapa. (A.P), India 3. P.G Scholar, Department of Civil Engineering, KSRM College of Engineering, Kadapa. (A.P), India ABSTRACT -- This paper investigates on physical and chemical properties clay and Bentonite for liner material. By the combination these liner material always fulfills low hydraulic conductivity for an effective long term behavior of land fill except hydraulic conductivity, the other properties such as shrinkage volume, unconfined compressive strength and compressibility play an important role in assessing long term behavior. In present study, clay and Bentonite used as barrier. The characteristics are determined with appropriate 2.5, 5 and 7.5% by weight of clay. Out of these percentages, mixer reduces the hydraulic conductivity, increase shear strength and reduce compressibility. Chemicals present in leachate production are also studied at Kadapa land fill site because combination of leachate presented in waste material. Key Words: Atterberg limit, Atomic adsorbent spectrometer. Compaction tests and unconfined compressive strength 1. INTRODUCTION The main task of the impermeable land fill liners is to reduce the migration of leachate to the ground water and reduced to reasonable amount. The important of landfill throughout world increases and need of engineered waste dumps is necessary. The practice of compacted clay liner (CCL) was started in the last three decades [1]. Land fill liners are exposed to various types of physical, chemical and biological processes which affected by leachate produced from the decomposition of waste dumps. Due to these the importance of Geo-technical characteristics of clay liners are determined in the laboratory. Decrease of ph correspondingly reduces the degree of adsorption capacity of clay on solutes as clay became more prorogated, thereby decreasing interaction between adsorbate and solute [2]. In order to reasonably predict transport of pollutants, it is significant to consider the effect of temperature on adsorption capacity of pollutants onto landfill liners [3]. Montmorillonite has large negative charge, due to this reason, it absorbs large quantity of hydrated cat ions and also it absorbs water molecules [4]. Bentonite can also increase the plasticity index of clayey soil [5]. When liquid interact with clay minerals, the properties which are increased and hydraulic conductivity tend to decrease [6]. The hydraulic conductivity of liner material is less than or equal to 1x10-7 cm/sec [7]. The low conductivity will be gained adequate strength and minimum shrinkage. From the previous reference by use of Kaolanite type of clay (lateritic soil) mixed with bentonite used as liner material [8]. Design guidelines used to frame the properties of the materials used as a barrier in landfills. So, that geotechnical properties and suitable to design parameter must be determined before construction [9]. Bentonite available in two states such as sodium bentonite and calcium bentonite, based on water adsorption capacity given by?[10]. Higher cat ion exchange of a liner material will result in a greater amount of inorganic contaminants being removed from the leachate. Soils with a minimum cat ion exchange of about 10meq /100gm are usually specified for liners [11]. Soils with high activity are more readily affected by pollutant if they are used in containment structures hence less active clayey soils are preferred for landfill liners [12]. The volume change upon drying of the compacted soil used as the liner material is less than 4% of OMC. For present study the minimum strength required for liner system should have unconfined compression strength of 200kPa (0.2N/mm 2 ). On the basis of this data the soil can be classified according to IS soil classification as inorganic clay with high compressibility (CH), Inorganic clay with high plasticity (CH) is typical material for landfill liners [13]. 2. EXPERIMENTAL INVISTIGATIONS Experimentation was programmed for conclusion of following Index properties of clayey soil and Bentonite clay. Suitability of clayey soil used as liner material based on hydraulic conductivity. Engineering properties of Blended soil (clay and Bentonite) such as unconfined compressive strength and shrinkage potential. Chemical properties such as ph, Cat ion exchange capacity etc. (clay, Bentonite and blended soils). Chemical properties for leachate. 2015, IJIRAE- All Rights Reserved Page - 274

2 3.MATERIALS International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: Clayey soil Clayey soil of Kaolanite mineral used as liner material it has hydraulic conductivity always lower than 1x 10-7 cm/sec. 3.2 Bentonite clay Montmorillonite type of clay has less pore space, relatively small pore spaces occupied by water and which leads to reduction of hydraulic conductivity of Montmorillonite. Bentonite can also increase the plasticity index of clayey soil in mm. Hence, it was preferred as blended soil. 3.3 Water Locally available bore well water has been used for mixing of soils. 4. PROPERTIES OF CLAY AND BENTONITE Fig.1: Clayey soil (Kaolanite mineral) It is necessary to perform laboratory experimentation for soil. Clod size my dependent on movement of leach ate trough soil. Mixer of soils such as different percentages of sand, silt and clay needed for present work. Some field tests were needed prior to construction. The tests were conducted according to IS specifications (Compendium of Indian standards on soil engineering; SP 36 (Part 1)-1987) for index properties of both clayey soil and bentonite clay. Clayey soil shows that it contains 15% of clay size fraction ( 0.002mm), 44.5% of silt and approximately 38% of sand. Based on the Atterberg limits of soil i.e. the liquid limit are 45.5%, plastic limit is 32.0% and plasticity index is 13.5%. On the basis experimental results the soil can be classified according to IS classification as inorganic silt with medium compressibility (MI). Medium compressibility inorganic silt (MI) and requires precise moisture control to achieve the desired compaction and may require a rubber-tired roller or sheep-foot roller. The particle size analysis of bentonite clay shows that the soil contains 80% of clay fraction ( 0.002mm) and 20% of silt. Atterberg limits of soil tested shows that the liquid limit is %, plastic limit is 44.57% and therefore plasticity index is Table.1 Recommended specifications for the soils to be used as liner material. (Teha et al 2004) PARAMETER REQUIREMENTS Percentage fines 50% Clay content 20-25% Liquid limit 25-30% Plasticity index 12-15% Cat ion exchange capacity 10 meq/100g Compressive strength of soil 20 kpa 2015, IJIRAE- All Rights Reserved Page - 275

3 Suitability of Blended soil Clayey soil was blended with 5% and 7.5% of bentonite clay. Compaction curves and the variation in hydraulic conductivity with moisture content were observed in the laboratory for determining the Geo-Technical properties. The results of compaction and hydraulic conductivity with varying percentage of bentonite clay added to clayey soil are tabulated in Table.2 Table. 2 Variation of hydraulic conductivity of blended soils Percentage of bentonite clay added Dry density (kn/m 3 ) Optimum moisture content Permeability in (cm/s) 2.5% % 3.51x10-7 5% % 8.51x % % 5.83 x10-8 Clayey soil mixed with 5% bentonite clay satisfies the criteria for hydraulic conductivity. Hence the blend with 5% and 7.5% bentonite clay were considered for further investigation. 5.1 CLAY MIXED WITH 5% BENTONITE CLAY Table.3 Variation of hydraulic conductivity with molding water content of clayey soil blended with 5% bentonite clay Dry density (kn/m 3 ) Molding water content Permeability (cm/s) % 6.56 x % 3.49 x (MDD) %(OMC) 8.51 x % 5.18 x % 6.19 x 10-8 The required hydraulic conductivity could not be achieved from clayey soil alone, it was blended with 5% bentonite clay and tested the blended soil according to IS specification. The minimum hydraulic conductivity at corresponding water content and dry density are presented in Table.3. It is evident that 5% bentonite clay blend satisfies the hydraulic conductivity criteria at initial saturation of 89% at optimum moisture content. Increasing water content generally results in an increased ability to break down clay aggregates and to eliminate inter aggregate pores UNCONFINED COMPRESSIVE STRENGTH (UCS) The compressive stress acting on the liner system is always two parameters they are? Height of the landfill and the unit weight of the waste. But up to date, the strength required to retain the liner material is not specified. some of the literatures given minimum strength, Daniel and Wu (1993) reported based on his experiments, present study the minimum strength required for liner system should have unconfined compression strength of 200kPa (0.2N/mm 2 ). Figure.2 Variation of unconfined compressive strength with axial strain 2015, IJIRAE- All Rights Reserved Page - 276

4 (Clayey soil + 5% bentonite clay) Figure.3 unconfined compressive strength Figure.4 Variation of unconfined compressive strength with molding water content (clayey soil+ 5% bentonite clay) Peak point obtained from graph is alarm to strength. Strength obtained from this mixer is not a maximum value it is always increase by increasing % of bentonite. At particular mix, the strength goes down at particular water content. 5.2 CLAY MIXED 7.5% BENTONITE CLAY The percentage of bentonite - clay was increased from 5% to 7.5% to achieve better. Figure.5 Standard compaction curve of clayey soil blended with 7.5% bentonite clay Based on these tests results the hydraulic conductivity tests were conducted on dry moisture content and wet of moisture content. It was found that the mixed soil satisfies the criteria for hydraulic conductivity at initial saturation of 86% at optimum moisture content. 2015, IJIRAE- All Rights Reserved Page - 277

5 Table.4 Variation of hydraulic conductivity with molding water content of clayey soil blended with 7.5% bentonite clay Dry density (kn/m 3 ) Molding water content Permeability (cm/s) % 2.10x % 2.12x (MDD) 20.5 %(OMC) 5.83 x % 5.21x % 5.20 x UNCONFINED COMPRESSIVE STRENGTH Figure.6 Variation of unconfined compressive strength with axial strain (clayey soil+ 7.5% bentonite clay) Figure.7 Variation of unconfined compressive strength with molding water content (clayey soil+ 7.5% bentonite clay) The results obtained from the unconfined compression test for different molding water content at different percentage are shown in Fig.6 and variation of unconfined compression test with respect to molding content for clay soil blended with 7.5% bentonite clay are shown in Fig.7. The strength of the compacted soil decreases with the increase in the molding water content. Test results for than the recommended minimum strength of 200kPa at 20.5% and 22.5% water content. 6. INDEX PROPERTIES OF BLENDED SOIL Literature suggests that plasticity index greater than 10% have been used successfully to construct soil liners with extremely low in-situ hydraulic conductivity and, Daniel (1991) states that if the plasticity index is less than 35, low shrinkage can be expected. The plasticity index increased by 7.23% and 10.24% for clayey soils blended with 5% and 7.5% bentonite clay respectively, and percentage of fines increased by 1.02 and 1.62 in both the cases. Soils with inadequate fines typically have too little silt and clay sized particles to produce high hydraulic conductivity. Hence a minimum of 50% fines is usually recommended for achieving low hydraulic conductivity. In addition shrinkage potential of a soil is directly related to its shrinkage limit. The shrinkage limit of the clayey soil blended with 5% and 7.5% bentonite clay obtained from laboratory tests are 18.64% and 18.42% respectively. 7. Acceptable water content The design of compacted clay liners an important parameter is the moisture content at which the soil attains maximum compaction. The maximum dry density that can be achieved with standard compaction and γ dmin indicates the minimum dry density at which soil mixture has an unconfined compressive strength of 200 kpa. 2015, IJIRAE- All Rights Reserved Page - 278

6 Figure.8 Acceptable zone based on hydraulic conductivity, standard compaction and unconfined compressive strength for clayey soil blended with 7.5% bentonite clay. The water content rang is the important key parameter to obtained maximum dry density (compaction) corresponding to hydraulic conductivity is less than 1x10-7 cm/s. The zone obtained these ranges is the acceptable rang is a range of maxi. And minimum dry density and moisture content values that will result in less than these values of hydraulic conductivity when effective and proper compaction. 8. CHARACTERSTICS OF LEACHATE The physical and chemical properties of soil primarily depend upon the waste compositions and water content present in waste. The leach ate samples were collected from the Kadapa dumping yard. The P H value of the collected sample was found to be 7.9. The relatively high values of Electrical conductivity (1.810 Ms) and Total dissolved solids ( mg/l) it indicates that presence of inorganic material in the samples. The presence of high COD (9625 mg/l) indicates the high organic strength. Among the nitrogenous compound, ammonium nitrogen (633 mg/l) was present in high concentration. This is due the domination of amino acids during the decomposition of organic compounds. The dark brown colour of the leach ate is mainly gives oxidation of ferrous to ferric form and formation of ferric hydroxide colloids and complexes with fulvic/ humid substances. The presence of Zinc (0.514 mg/l) in the leach ate shows that the landfill receives waste from barriers and fluorescent lamps. The presence of lead (0.77 mg/l) in the leach ate sample indicates the disposal of lead barriers, chemicals for photograph processing and pipes at site. 9. RESULTS Based on the experimental investigation the following are some of the important conclusions. 1. Hydraulic conductivity of clayey soil was found to be 2.4 x 10-6 cm/sec which is not acceptable as per the relevant standards. Hence clayey soil was mixed with bentonite clay. 2. Based on the Hydraulic conductivity (1x10-7 cm/sec), the clayey soil mixed with 7.5% bentonite clay satisfies the criteria for hydraulic conductivity. To achieve the desired hydraulic conductivity, degree of saturation shall be maintained 95% to 88%. Also hen the saturation level is 95 % to 88 % the observed maximum dry density and OMC values were in range (i.e. γ d max = kn/m 2 to15.4 kn/m 2 and OMC = 20.5 % to 22.5 % ) 3. When mixed soil is compacted to desired maximum dry density (i.e. γ d max = kn/m 2 to15.4 kn/m 2 ) at acceptable water content.(i.e % to 22.5%) its compressive strength was kpa and kpa (>200 kpa) with minimum shrinkage potential. 4. Higher Cation exchange of a liner material will result in a greater amount of inorganic contaminants being removed from the leachate (Kayabali 1997). Soils with a minimum cat ion exchange of about 10meq /100gm are usually specified for liners. The results obtained clay- Bentonite mixer, cat ion exchange capacity of the clayey soil blended with 5% and 7.5% bentonite clay tested in this study as meq/100g and meq/100g respectively. Thus from the CEC or contaminant attenuation capacity point of view, the blended soils are more suitable for liner material. 5. The ph value of the collected sample was found to be 7.9. The relatively high values of Electrical conductivity (1.810 Ms) and Total dissolved solids ( mg/l) it indicates that presence of inorganic material in the samples. 6. The presence of high COD (9625 mg/l) indicates the high organic strength. 10. REFERENCES 1. Daniel, D.E. and Benson, C.H. (1990). Water content density criteria for compacted soil liners. Journal of Geotechnical Engineering, ASCE 116 (12), pp Ameta, N.K. and Abhay S. W. (2008). Effect of bentonite on permeability of dune sand. Electronic Journal of Geotechnical Engineering., 13, pp , IJIRAE- All Rights Reserved Page - 279

7 3. Mitchell, J.K.:1993, Fundamentals of soil Behavior, 2 nd ed.,wiley, New York. 4. Grim, R.E.: 1968, Clay Mineralogy, 2 nd ed., McGraw-Hill, New York. 5. Ziaie-Moayed, R. and Naeini, S.A.:2009, Effect of plasticity index and reinforcement on the CBR value of soft clay, International Journal of Civil Engineering, 7:2, Alawaji, H.A.: 1990, Swell and compressibility characteristics of sand-bentonite mixers inundated with liquids, Applied Clay Science, 15, Kolawole, J., Osinubi, and Charles M. O. (2005). Hydraulic Conductivity of compacted lateritic soil. Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 131, Ameta N.K. and Abhay Shivaji Wayal : "Effect of Bentonite on Permeability of Dune Sand". E.J.G.E., Vol. 13 Bundle A, Winter, 2007, Design guidelines for landfill liners. 10. Gleason et al., characteristics of bentonite, suitability of bentonite for blended material. 11. Sahel, N. A. and Ali M. D. (2001). Selection of liner materials and design of hazardous water facilities in Saudi Arabia. Science and Technology Journal, 6, Smith, D. C. and Martin, V. F. (1996). Chemical manipulation of soil for sealing landfill. Applied Geochemistry Journal, 11, Teha, (2004). Classification of soils on plasticity characteristics for landfill liner materials. 2015, IJIRAE- All Rights Reserved Page - 280