Utilization of bentonite silt mixtures as seepage barriers in liner systems

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Utilization of bentonite silt mixtures as seepage barriers in liner systems

  1. 1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME346UTILIZATION OF BENTONITE-SILT MIXTURES AS SEEPAGEBARRIERS IN LINER SYSTEMS OF ENGINEERED LANDFILLSNitish Puri1and Deepak Soni21(Assistant Professor, Department of Civil Engineering, GCET, Greater Noida, Uttar Pradesh, India)2(Assistant Professor, Department of Civil Engineering, GIMT, Kurukshetra, Haryana, India)ABSTRACTThe permeability and compaction characteristics of several bentonite-silt mixtureswere determined and effects of bentonite content on the above stated characteristics wereinvestigated. Standard proctor test were conducted on both silts and silts stabilized with 3, 6,9, 12 and 15% of bentonite clay by weight. For both type of silts values of MDD increasesand OMC decreases with increase in percentage of bentonite as an additive. To ensureconsistent performance of these clay liners, they were compacted to maximum dry density(MDD) by adding optimum moisture content (OMC). Falling head permeability test wereconducted on compacted plastic and non-plastic silt samples stabilized with 3, 6, 9, 12 and15% % of bentonite clay by weight. The permeability values for all silt-bentonite mixtureswere measured. A Significant decrease in values of permeability was observed for both typesof silt-bentonite mixtures with increase in percentage of bentonite clay as an additive.Keywords: Permeability, compaction, clay liners, bentonite, maximum dry density andoptimum moisture content1. INTRODUCTIONModern landfills are engineered containment systems, designed to minimize theimpact of solid waste (refuse, trash, and garbage) on the environment and human health. Inmodern landfills, the waste is contained by a liner system. The primary purpose of the linersystem is to isolate the landfill contents from the environment and, therefore, to protect thesoil and ground water from pollution originating in the landfill. The greatest threat to groundwater posed by modern landfills is Leachate. Leachate consists of water and water-solublecompounds in the refuse that accumulate as water moves through the landfill. This water maybe from rainfall or from the waste itself. Leachate may migrate from the landfill andcontaminate soil and ground water, thus presenting a risk to human and environmental health.INTERNATIONAL JOURNAL OF CIVIL ENGINEERING ANDTECHNOLOGY (IJCIET)ISSN 0976 – 6308 (Print)ISSN 0976 – 6316(Online)Volume 4, Issue 2, March - April (2013), pp. 346-352© IAEME: www.iaeme.com/ijciet.aspJournal Impact Factor (2013): 5.3277 (Calculated by GISI)www.jifactor.comIJCIET© IAEME
  2. 2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, MarchLandfill liners are designed and constructed to create a barrier between the waste and thenvironment and to drain the Leachateprevent the uncontrolled release oflow permeability are often used as seepage barriers in liner systems oWhen such types of clays are unavailablehigh plastic imported clays or commercially available clays such as bentonite to achievemixtures of desired values of permeability. Coefficican be 10-8cm/sec or less and having a thickness of 100 cm or moretwo silty soils of plastic and non-bentonite clay to reduce their permeability.2. LITERATURE REVIEW2.1 GeneralWaste is a by-product of human activity that cannot be put to any use. The termwaste’ refers to waste that is solid.It can be dry moist or wet and it remains at the location where it is deposited.waste is dumped on open ground, it causes the following environmental problems:a) Ground water contamination through seepage of Leachate into the ground.b) Surface water contamination through erosion of fine particles of waste as well asLeachate run-off from sides of dump.c) Local air contamination due to fugitive dust, gaseous emissions,bad odour.d) Other problems like increase in rodents and pests,garbage/dry leaves/plastics. Bird menace to overhead airblockage of surface water drainage paths due to alteration of natural topographyarea.These harmful effects of waste dump can be minimizedthat is, by isolating it from the environment.liner at the base of the waste and an impermeable cover at the top of the wastewaste disposal facility as shown inFig.2.1 Schematic drawing of an engineered landfill.International Journal of Civil Engineering and Technology (IJCIET), ISSN 09766316(Online) Volume 4, Issue 2, March - April (2013), © IAEME347Landfill liners are designed and constructed to create a barrier between the waste and thLeachate to collection and treatment facilities. This is done toprevent the uncontrolled release of Leachate into the environment. Compacted clays havinglow permeability are often used as seepage barriers in liner systems of engineered landfills.unavailable then in-situ soils must be treated with medium tohigh plastic imported clays or commercially available clays such as bentonite to achievemixtures of desired values of permeability. Coefficient of permeability for seepage barrierscm/sec or less and having a thickness of 100 cm or more [6]. In the present study,-plastic nature have been stabilized with small percentages ofe their permeability.product of human activity that cannot be put to any use. The termwaste’ refers to waste that is solid.It can be dry moist or wet and it remains at the location where it is deposited.waste is dumped on open ground, it causes the following environmental problems:Ground water contamination through seepage of Leachate into the ground.r contamination through erosion of fine particles of waste as well asoff from sides of dump.Local air contamination due to fugitive dust, gaseous emissions, wind-blownOther problems like increase in rodents and pests, risk of fire from burninggarbage/dry leaves/plastics. Bird menace to overhead air crafts, slope failures andblockage of surface water drainage paths due to alteration of natural topographyThese harmful effects of waste dump can be minimized by containing the solid waste,that is, by isolating it from the environment. This can be done by providing an imperviousliner at the base of the waste and an impermeable cover at the top of the waste [7]as shown in Fig. 2.1 below is called as landfill.Schematic drawing of an engineered landfill. Source: Bonaparte et al. (2002)International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308IAEMELandfill liners are designed and constructed to create a barrier between the waste and theto collection and treatment facilities. This is done toCompacted clays havingf engineered landfills.situ soils must be treated with medium tohigh plastic imported clays or commercially available clays such as bentonite to achieveent of permeability for seepage barriersIn the present study,been stabilized with small percentages ofproduct of human activity that cannot be put to any use. The term ‘solidIt can be dry moist or wet and it remains at the location where it is deposited. When solidwaste is dumped on open ground, it causes the following environmental problems:Ground water contamination through seepage of Leachate into the ground.r contamination through erosion of fine particles of waste as well asblown litter andrisk of fire from burning, slope failures andblockage of surface water drainage paths due to alteration of natural topography of theby containing the solid waste,This can be done by providing an impervious[7]. This solidSource: Bonaparte et al. (2002)
  3. 3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME3482.2 RequirementsThe most critical component of a liner or a cover is the impervious barrier. Such abarrier is expected to meet the following requirements:a) It should be impervious and should behave monolithically over several hundredsquare metres of land areas.b) It should be flexible and remain intact under settlement of subsoil or of waste.c) It should be durable for the design life of landfill.d) It should be strong enough to withstand stresses imposed by filled wastes and byvehicles moving on it.Clay meets most of the requirements of a barrier layer. Table 2.1 shows requiredcharacteristics of clay liners.Characteristics Clay linerThickness 0.6 – 1.5 mPermeability 10-8m/sec or lessDensity MDD determined as per testsMoisture content OMC determined as per testsShear strength UCS determined as per testsTable 2.1 Requirements for a good clay linerNote: First two parameters are considered important for clay liners.3. MATERIALS3.1 Bentonite clayIt was collected from Laxmi Lining Material Pvt. Ltd, Opposite Royal Palace, Sodal Road,Preet Nagar, Jalandhar – 144004. It is classified as clay of high compressibility, CH, as perclassifications of IS: 1498 (1970) [3]. Its physical and engineering properties are reported inTable 3.1.3.2 SiltTwo types of silts were collected, one from village Ramdaspur and other from village Ajnalaof District Amritsar. Both silts were classified as silt of low compressibility, ML, as perclassifications of IS: 1498 (1970) [3]. There physical and engineering properties are reportedin Table 3.1.
  4. 4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME349CharacteristicsMaterialsSilt I Silt II BentoniteSpecific gravity (G) 2.71 2.7 -Atterberg’slimitsLL 22 25 265PL NP 19 46PI NP 6 219CompactioncharacteristicsMDD (g/cc) 1.62 1.82 -OMC (%) 14.9 13.2 -Colour Brown Light Brown YellowClassificationSilt of lowcompressibilitySilt of lowcompressibilityClay of highcompressibilityGroup ML ML CHGrain sizedistributionClay 0% 15% 88%Silt 87% 66% 12%Sand 13% 19% 0%Unconfined compressivestrength (UCS) in kg/cm2 1.02 0.92 -Table 3.1 Characterization of materials4. EXPERIMENTAL INVESTIGATIONA series of falling head permeability test were conducted on bentonite-silt mixtures toevaluate their performance as a clay liner in landfills. These tests were performed as per thespecifications of IS: 2720 (Part 17) (1966) [5]. Standard proctor tests were conducted on siltsand silts stabilized with 3, 6, 9, 12 and 15% of bentonite by weight. These tests wereconducted in order to prepare specimens at maximum dry density by adding desired optimummoisture content as per specifications of IS: 2720 (Part 7) (1974) [4].4.1 Moisture-density relationshipsStandard Proctor tests have been conducted to determine optimum moisture content(OMC) and maximum dry density (MDD) of silts stabilized with various varying percentagesof bentonite clay. Fig 4.1(a) and Fig 4.2 (b) show comparison of MDD and OMC for siltsstabilized with bentonite clay and these values are reported in Table.4.1.For silt I, MDD and OMC were observed as 1.62 g/cc and 14.9% respectively. For silt II,MDD and OMC were observed as 1.82 g/cc and 13.2 % respectively. For silt I stabilizedwith bentonite MDD varies from 1.62 to 1.73 g/cc and OMC varies from 14.9 % to 13.42 %.It has been observed that for silt I MDD increases and OMC decreases with increase inpercentage of bentonite as an additive. For silt II MDD varies from 1.82 g/cc to 1.91 g/cc andOMC varies from 13.2% to 12.43%. Also for silt II, it has been observed that MDD increasesand OMC decreases with increase in percentage of bentonite as an additive.
  5. 5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME350Table 4.1 Values of MDD and OMC for bentonite-silt mixturesFig. 4.1 (a) Variation of MDD vs. Percentage of bentonite as an additiveFig. 4.1 (b) Variation of OMC vs. Percentage of bentonite as an additive4.2 Permeability characteristicsFor silt I and silt II permeability has been observed as 5.5 x 10-6cm/s and 2.96 x 10-7respectively. For bentonite-silt I mixtures permeability varies from 5.5 x 10-6cm/s to 1.07 x10-8cm/s. Hence total reduction in permeability was 99.81 %. It has been observed thatpermeability decreases significantly with increase in percentage of bentonite as stabilizer. Forbentonite-silt II mixtures permeability varies from 2.96 x 10-7cm/s to 0.91 x 10-8cm/s.Which means total reduction in permeability was 99.69 %.1.61.651.71.751.81.851.91.950 5 10 15 20Maximumdrydensity(MDD)ing/ccPercentage of bentonite as stabilizer (%)Silt ISilt II1212.51313.51414.51515.50 5 10 15 20Optimummoisturecontent(%)Percentage of bentonite as stabilizer (%)Silt ISilt II
  6. 6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME351Table 4.1 Values of permeability (k) in cm/sec for bentonite-silt mixturesSamplePercentage of bentonite as an additive0% 3 6 9 12 15%Silt I+Bentonite5.5 x 10-62.3 x 10-67.8 x 10-76.1 x 10-7 2.97 x 10-8 1.07 x 10-8Silt II+Bentonite2.96 x 10-7 1.02 x 10-7 9.8 x 10-88.7 x 10-84.7 x 10-89.1 x 10-9Fig.4.2 Variation of permeability (K) with percentage of bentonite as additiveFig. 4.2 Variation of permeability with percentage of bentonite as an additive5. CONCLUSIONSThe study demonstrates the influence of bentonite clay on the permeability andcompaction characteristics of locally available silts. The following conclusions have beendrawn based on the laboratory investigations carried out in this study:1. For both type of silts values of MDD increases and OMC decreases with increase inpercentage of bentonite as an additive. Which means better compaction can beexpected from these silt-bentonite mixtures. Similar results reported by otherinvestigators.[1]2. A Significant decrease in values of permeability was observed for both types of silt-bentonite mixtures with increase in percentage of bentonite clay as an additive.3. Silt-bentonite mixtures containing silt II performed well as compared to mixturescontaining silt I. Hence it is recommended that plastic silts in combination withbentonite should be used as clay liners if available.0.00E+001.00E-062.00E-063.00E-064.00E-065.00E-066.00E-060 5 10 15 20Permeability(k)incm/sPercentage of bentonite as an additive (%)Silt ISilt II
  7. 7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308(Print), ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME3524. Percentage of bentonite should be maintained between 10 to 15 % because beyondthat extent further improvement in permeability is not possible and also noteconomical. Similar results were reported by other investigators.[2]5. It is also recommended to use locally available clays similar to bentonite if present.REFERENCES[1] Cho, Won-Jin, Lee, Jae-Owan and Kang, Chul-Hyung (2002),”Hydraulic Conductivityof Compacted Soil-Bentonite Mixture for A Liner Material in Landfill Facilities”,Environmental Engineering Research, Vol.3, 122-127, Korean Society ofEnvironmental Engineers.[2] Mollins, L.H, Stewart, D.I and Cousens, T.W (1996),” Predicting the Properties ofBentonite-Sand Mixtures”, Clay Minerals, Vol. 31, 243-252.[3] IS: 1498 (1970),”Indian Standard Methods of Test for Soils: Classification andIdentification of Soil for General Engineering Purposes”, Bureau of Indian Standards.[4] IS: 2720 (Part 7) (1974), “Indian Standard Methods of Test for Soils: Determination ofMoisture Content-Dry Density Relation using Light Compaction”, Bureau of IndianStandards.[5] IS: 2720 (Part 17) (1966), “Indian Standard Methods of Test for Soils: LaboratoryDetermination of Permeability”, Bureau of Indian Standards.[6] Singh, Alam and Chowdhary, G.R. (1994), “Soil Engineering in Theory and Practice”,Geotechnical Testing and Instrumentation, Vol. 2, CBS Publishers and Distributors,Delhi.[7] Ghulati, Shashi K and Datta, Manoj (2012), “Geotechnical Engineering”, 15thReprint,Tata McGraw Hills Education Private Limited, New Delhi.[8] V.S.Tamilarasan, Dr.P.Perumal and Dr.J.Maheswaran, “Experimental Study on WaterPermeability and Chloride Permeability of Concrete with GGBS as a ReplacementMaterial for Cement”, International Journal of Civil Engineering & Technology(IJCIET), Volume 3, Issue 2, 2012, pp. 25 - 40, ISSN Print: 0976 – 6308, ISSN Online:0976 – 6316.[9] M. Vijaya Sekhar Reddy, Dr. I.V. Ramana Reddy and N.Krishna Murthy, “Durabilityof Standard Concrete Incorporating Supplementary Cementing Materials using RapidChloride Permeability Test”, International Journal of Civil Engineering & Technology(IJCIET), Volume 3, Issue 2, 2012, pp. 373 - 379, ISSN Print: 0976 – 6308, ISSNOnline: 0976 – 6316.[10] Mukesh A. Patel and Dr. H. S. Patel, “Correlation Between Physical Properties andCalifornia Bearing Ratio Test on Soils of Gujarat Region in Both Soak andUnsoak Condition”, International Journal of Civil Engineering & Technology (IJCIET),Volume 3, Issue 2, 2012, pp. 50 - 59, ISSN Print: 0976 – 6308, ISSN Online: 0976 –6316.

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