sedimentary residual soil as a waste containment barrier material

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Soil & Sediment Contamination, 13:407–420, 2004Copyright © ASPISSN: 1058-8337 print / 1549-7887 onlineDOI: 10.1080/10588330490500446

Sedimentary Residual Soil as a Waste ContainmentBarrier Material

MD. HUMAYUN KABIRMOHD RAIHAN TAHA

Faculty of EngineeringUniversity Kebangsaan MalaysiaSelangor, Malaysia

Compacted soil liners are widely used as a waste containment barrier to control orrestrict the migration of contaminant/leachate from the landfill into the environmentbecause of their low hydraulic conductivity, attenuation capacity, resistance to damageor puncture, and cost effectiveness. Compacted soil liners are usually composed of nat-ural inorganic clays or clayey soils. If natural clayey soils are not available, kaoliniteor commercially available high swelling clay (bentonite) can be mixed with local soilsor sand. This study examines the potential of a sedimentary residual soil as a wastecontainment barrier in landfills. The laboratory experiments conducted were: grain sizedistribution, Atterberg limits, swelling tests, compaction, volumetric shrinkage strain,unconfined compression, hydraulic conductivity and cation exchange capacity. The ex-perimental results were compared with those recommended by various researchers forevaluation of its suitability. Test results showed that the soil compacted with modifiedProctor compaction effort possesses low hydraulic conductivity (≤1 × 10−7 cm/s) andadequate strength. In addition, compacted sedimentary residual soil exhibited little vol-umetric shrinkage strain of below 4% at this compaction effort. Thus, the sedimentaryresidual soil could be effectively used for the construction of a waste containment barrierin landfills.

Keywords Compacted soil liner, waste containment barrier, sedimentary residual soil,activity, hydraulic conductivity, volumetric shrinkage.

1. Introduction

Landfills are physical facilities used for the disposal of waste materials in the subsurface. Inmodern solid waste management, many countries still consider landfilling as the preferredmeans of disposing waste materials. In landfills waste materials interact with moisturereceived from rainfall and snow, and generate toxic leachates or contaminants. In orderto avoid uncontrolled release of contaminants into the environment, the waste materialsare required to be totally encapsulated and this is undertaken by the use of liner sys-tem. Environmental protection agencies of various countries have specified that compactedclayey soil may be used as an effective barrier for the containment of landfill leachate.Clayey soil is favored for its low hydraulic conductivity. In addition, clayey soil attenuates

Address correspondence to M. H. Kabir, Department of Civil and Structural Engineering, Facultyof Engineering, University Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia. E-mail:[email protected]

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408 M. H. Kabir and M. R. Taha

chemicals to varying degrees, by lowering pollutant concentrations as the leachate migratesthrough the compacted soil layer (Mohamed and Antia, 1998). However, the primary factorscontrolling the performance of clay liners are the hydraulic conductivity, strength, andshrinkage potential of the soil with water content as an index (Oweis and Khera, 1998).

For use as waste containment barriers, compacted clay liners should have a hydraulicconductivity of at least 1 × 10−7 cm/s and a minimum thickness of about 0.9-1 meter(Schevon and Damas, 1986; Peyton and Schroeder, 1990; Daniel, 1993; Benson and Daniel,1994; Rowe et al., 1995; Arch, 1998; Mohamed and Antia, 1998). Literature has suggestedthat a hydraulic conductivity of ≤1 × 10−7 cm/s is achievable if suitable material (clayeysoil) is excavated, reworked, or homogenized and laid down in lifts following appropriateconstruction protocol on a properly prepared sub-base. Key properties in achieving lowhydraulic conductivity are the plasticity index and clay content of the soil. Low plastic soilis preferable over highly plastic soil, as soils with low plasticity are often easier to mix,hydrate, and homogenize in the field and tend to be less susceptible to desiccation cracking.However, the plasticity index should be less than 30%; otherwise the soil becomes stickywhen wet and may form large clods. It then becomes difficult to construct, as experiencedboth in the laboratory and in the field by Elsbury et al. (1988).

Desiccation cracks occur in compacted clay liner (CCL) due to evaporative waterlosses, which can cause shrinkage of the soil (Oakley, 1987). This crack can lead to pref-erential leachate migration flow paths and therefore an increase in the clay liner’s effectivepermeability. Desiccation shrinkage increases with increasing clay content (Dejong andWarkentin, 1965; Kleppe and Olson, 1985). The volume change or shrinkage behavior ofsoil is directly related to the shrinkage limit. Soils with high shrinkage limits (12% or more)offer less/little volume change potential with change in moisture content (Lutton et al.,1979). Thus, soils with high shrinkage limits are preferable to those with lower shrinkagelimits in liner construction. However, the literature suggested that clay liner does not exhibitdesiccation cracking if the volume change upon drying of the compacted soils used for lineris less than about 4% (Daniel and Wu, 1993; Tay et al., 2001).

There are several stresses that are imposed on the CCL in a landfill during constructionand operation. Thus, compacted soils used for liner must have adequate strength for stability.The bearing stress acts on the CCL depends on the height of landfill and the unit weight ofwaste. Thus, to date, the minimum required strength of soil used for CCL is not specified.Daniel and Wu (1993) arbitrarily selected them to support the maximum bearing stress ina landfill. They mentioned that soil used for clay liner should have minimum unconfinedcompression strength of 200 kPa. Fine soils with a significant amount of granular content(sand plus gravel >50%) offer notable protection from volumetric shrinkage (Hewitt andPhilip, 1999) and impart adequate strength as well.

In addition, soils used in clay liners should have the ability to attenuate contami-nant/leachates and should be compatible with the contaminant to be retained. Clays andclay minerals play an important role in increasing contaminant removal capacity as wellas in reducing hydraulic conductivity of soil because of their large specific surface areaand high cation exchange capacity (Oweis and Khera, 1998; Czurda and Wagner, 1991).The attenuation of positively charged chemical species in leachate through a clay liner isa function of cation exchange capacity (CEC) of the liner material. Higher CEC of a clayliner material will result in greater amount of cationic contaminants being removed fromthe leachate (Kayabali, 1997). Rowe et al. (1995) recommended that soils with a minimumCEC of about 10 meq per 100 g of soil might be specified for clay liner.

It is desirable for waste containment systems to achieve its required purposes at min-imum cost. Careful consideration should therefore be given to the choice of materials for

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Sedimentary Residual Soil as a Waste Containment Barrier Material 409

barrier systems. Approximately about half the area of the Peninsular Malaysia is coveredwith sedimentary residual soil. The sedimentary residual soil is a residual soil in whichits particles are derived from sedimentary rocks. Its potential use in liner system may sig-nificantly reduce the cost of construction of the waste containment facilities. The aim ofthis study was to explore the physio-chemical properties, hydraulic conductivity behavior,shrinkage potential and strength characteristics of sedimentary residual soil. This studyemployed basic tests of soil, swelling test, compaction, volumetric shrinkage strain, uncon-fined compression, hydraulic conductivity and cation exchange capacity of soil to evaluatewhether the soil could be used for the construction of liner in landfills.

2. Material

The soil that was used for this study is sedimentary residual soil. The soil was obtainedfrom a site within the main campus of the University Kebangsaan Malaysia (UKM) inBangi, Selangor. The soils were excavated with a shovel from the depth of 0.6 m belowthe profile to avoid humus layer and roots, placed in plastic bags, and transported to thegeotechnical laboratory of University Kebangsaan Malaysia. Then, the soils were removedfrom the plastic bags, carefully blended, and stored in a plastic container.

3. Methods

3.1 Basic Tests

The specific gravity, pH and organic content measurements of the soil were performedaccording to British Standard (BS1377:1990) as documented in Head (1992). Particle sizedetermination of the soil was carried out by direct sieving of the sand fraction and by thehydrometer method for silt and clay. The liquid and plastic limit was determined by fallcone method. The data of these index properties were used to classify the soil in the UnifiedSoil Classification System (USCS).

3.2 Processing of Soil

The soil was air dried and crushed with a rubber hammer to break up dried soil crumb intosmall pieces. The crushed soils were then passed through a No. 4 sieve (4.75 mm openings).Soil clods that remained on the sieve were broken down by hand until they passed throughthe sieve. The sieved soils were wetted with tap water (pH = 6.65) using a spray bottle,and stirred with a trowel during hydration to ensure an even distribution of water to achievethe desired water content. Afterward the moistened soils were sealed in plastic bags andstored for at least 3 days to allow moisture equilibration and hydration. The processed soilwas used for compaction, hydraulic conductivity, volumetric shrinkage and compressivestrength tests.

3.3 Compaction Tests

The soil was compacted with three energies (modified, standard, and reduced) as recom-mended by Daniel and Benson (1990). The modified and standard Proctor tests were doneaccording to BS methods (BS1377: Part 4:1990:3.3 and BS1377: Part 4:1990:3.5). Reducedcompaction was identical to standard compaction except that only 15 blows of the hammer

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per lift were applied rather than the usual 27 blows. This range of energy was selected inan effort to bracket the range of reasonable compactive energy (Daniel and Wu, 1993).

3.4 Hydraulic Conductivity Tests

The hydraulic conductivity was measured in 1 liter compaction mold with perforated base(rigid wall permeameter) under falling head condition as recommended by Head (1994).Processed soils were compacted with three energies (modified, standard, and reduced) atdifferent water content within the molds. Then the molds were placed in a sink in whichthe water level was about 50 mm above the top surface of compacted samples while theair bleed valve was opened so that the water could back up through the specimens. Thisprocedure was applied to ensure saturation of the samples and to eliminate entrapped air.Test specimens were free to swell vertically (i.e., no vertical stress was applied). Thepermeant liquid was deaired tap water, and hydraulic gradient was 15. Permeation wasconducted on the samples until steady conditions (h3 = √

(h1 ×h2)) were achieved. Duringeither saturation or permeation of water no air pressure was applied. The experiment wasconducted in triplicate for each particular soil condition to increase the reliability of the testresults.

3.5 Volumetric Shrinkage Tests

The volumetric shrinkage upon drying was measured by extruding compacted cylindricalspecimens from the compaction molds and allowing the cylindrical specimens to dry ona laboratory table in an air-conditioned room (Daniel and Wu, 1993). Four measurementsof diameter and six measurements of height were obtained every day with a digital caliperaccurate to 0.01 mm. The average diameter and height were used to compute volume, andthe measurements were continued until the volume ceased to change further.

3.6 Unconfined Compression Tests

In this study, the unconfined compression test as performed in accordance with the ASTMD2166 procedure, a test method for unconfined compressive strength of cohesive soils.The test as performed on cylindrical specimens having a diameter and length of 50 mmand 100 mm respectively, which were trimmed from the larger compacted cylinders. Thesamples were tested in triaxial compression test machine without applying cell pressure.The rate of strain applied was 0.83% per minute (Mohamed et al., 2002).

3.7 Swelling Tests

Free swell (FS) test was carried out to determine the swelling potentials. It is one of themost commonly used test to estimate the swelling potential of soil. This test, as suggestedby Holtz and Gibbs (1956), was performed by pouring 10 cm3 of dry soil through a 425 µmsieve into a 50 cm3glass measuring cylinder filled with distilled water, noting the swelledvolume of the soil when it came to rest.

3.8 Cation Exchange Capacity

United States EPA test method 9081 (sodium acetate) was followed to measure the cationexchange capacity of soil. The soil sample was mixed with an excess of sodium acetate

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solution, resulting in an exchange of the added sodium cations for the matrix cations. Sub-sequently, the sample was washed with isopropyl alcohol. An ammonium acetate solutionwas then added, which replaces the adsorbed sodium with ammonium. The concentrationof displaced sodium was then determined by Inductively Coupled Plasma—Mass Spec-trometer (ICP-MS).

4. Experimental Results and Discussions

4.1 Basic Properties

The basic properties of the sedimentary residual soil are listed in Table 1.

Organic Content

The soil contains 0.63% of organic matter. Organic matter has a stabilizing effect (increasesthe cohesion of clay fractions) on soil structure, improves the moisture holding capacity andprotects soils against erosion (Batjes and Bridges, 1992). But the presence of large amountsof organic matter in soils is usually undesirable from the engineering point of view. Thoughorganic matter increases the cation exchange capacity and decreases the permeability of soil,it may cause high plasticity, high shrinkage, high compressibility and low strength (Mitchell,1976). However, the sedimentary residual soil contains a small amount of organic matter,which may not significantly affect its physio-chemical properties.

pH

The soil possesses pH of 4.95. According to U.S. Department of Agriculture, Natural Re-sources Conservation Service (2003), this is a very strongly acidic soil. pH has stronginfluences on cation adsorption capacity as well as structure of clay because hydrogenions play active role in both chemical and physical bonding processes (Mohamed andAntia, 1998). In low pH, the edges of the clay particles ionize positively, thus encour-aging edge-to-face contacts. The clay particles flock to each other in a random fash-ion with edge-to-face orientation yielding a flocculated structure. Clayey soil that hasflocculent structure possesses high void ratio (Das, 1998). Thus, soil may exhibit man-ifold variations in hydraulic conductivity as a result of changes in void ratio (Mitchell,1976).

Table 1Basic properties of sedimentary residual soil

Sand fraction(2 to 0.063 mm)

(%)

Silt fraction(0.063 to

0.002 mm)(%)

Clay fraction(<0.002 mm)

(%)Specificgravity

Liquidlimit(%)

Plasticlimit(%) pH

Organiccontent

(%)

59 18 23 2.596 36 17.2 4.95 0.63

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Figure 1. Particle size distribution curve.

Particle Size Distribution and Atterberg Limits

Figure 1 shows the results of particle size analysis. The soil contains 42% fines (<0.075 mm),whereas a zero percent was retained on No. 4 sieve (opening = 4.75 mm). Moreover, theresults of Atterberg limits reveal the liquid limit (LL) = 36%, the plastic limit (PL) =17.2% and the plasticity index (PI = LL – PL) = 18.8%. On the basic of these data, thesedimentary residual soil is classified as SC (clayey sand) according to the Unified SoilClassification System. The data presented here suggest that sedimentary residual soil hassimilar properties to cohesive soils, and therefore is likely to have desirable characteristicsto minimize hydraulic conductivity.

Activity

The activity [PI/% clay fraction] of sedimentary residual soil is about 0.82. Thus, accordingto Skempton’s classification (1953) it is normal clay. Activity is an index of the surfaceactivity of the clay fraction. Soils with higher activity are likely to consist of smaller particleshaving larger specific surface area and thicker electrical double layers. Thus hydraulicconductivity should decrease with increasing activity. Benson et al. (1994) collected data(index properties, water content, dry unit weight, initial saturation, hydraulic conductivity,etc.) from 67 landfills at various locations in North America. Their graphical presentation ofthe data (hydraulic conductivity as a function of activity) also shows the trend of decreasinghydraulic conductivity with increasing activity. However, soils with high activity are notrecommended for use in landfill liners or containment structures as they are more readilyaffected by pollutant (Oweis and Khera, 1998).

Particle size distribution, Atterberg limits and activity of a soil influences the hy-draulic conductivity. For use as waste containment barrier, soil should have a hydraulicconductivity of at least 1 × 10−7 cm/s. Benson et al. (1994) suggested that hydraulicconductivity of ≤1 × 10−7 cm/s could be achieved if the soil possesses the following in-dex properties: percentage fines ≥30%, percentage of clay ≥15%, liquid limit (LL) ≥20,plasticity index (PI) ≥7, and activity ≥0.3. The comparison between the index proper-ties of sedimentary residual soil and the index properties as suggested by Benson et al.

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Figure 2. Compaction curves for sedimentary residual soil.

(1994) shows that sedimentary residual soil has suitable properties to use as hydraulicbarrier.

4.2 Compaction Properties

The compaction curves for sedimentary residual soil are shown in Figure 2. The curvesare parabolic in shape, which is typical of most clayey soils. The curves represent therelationship between dry density and water content obtained from the modified, standard andreduced Proctor compaction tests, respectively. Compaction curve is plotted to determine theoptimum water content corresponding to maximum dry density (peak of the compactioncurve) for a soil under a specific compactive effort. The maximum dry density and theoptimum water content obtained from these curves are given in Table 2. An increase incompactive effort increases the maximum dry density but decreases the optimum watercontent. Because higher compactive effort yields a more parallel orientation to the clayparticles, which gives a more dispersed structure, the particles become closer and porosityreduces.

Compaction of soils increases their density and strength, and reduces their hydraulicconductivity. The compaction parameters and their effects on hydraulic conductivity, shrink-age and strength are discussed in the following sections.

Table 2Maximum dry density and corresponding optimum water

content of sedimentary residual soil

Optimum water Max. dry density,Compactive efforts content, wopt (%) γd (kN/m3)

Modified Proctor 12.4 18.95Standard Proctor 15.8 17.48Reduced Proctor 17.4 16.72

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4.3 Hydraulic Conductivity

The hydraulic conductivity test was conducted in triplicate for each particular soil condition.Results of the three replicate measurements of hydraulic conductivity and their averagesfor reduced, standard, and modified Proctor efforts are shown in Table 3. For a particularsoil condition each replication yielded almost identical results. The variations among thethree replicate measurements did not exceed 25%. The average of the three replicate mea-surements was considered as the hydraulic conductivity for each particular soil condition.The relationship between average hydraulic conductivity, water content and compactiveeffort is shown in Figure 3. The hydraulic conductivity decreases with the increasing com-pactive effort. Because increasing compactive effort decreases the frequency of large poresand can eliminate the large pore mode (Acar and Oliveri, 1989). These changes in poresize yield lower hydraulic conductivity. The hydraulic conductivity also changes with thechange of compaction water content. Soils compacted at dry of optimum water content tendto have relatively high hydraulic conductivity whereas soils compacted at wet of optimumwater content tend to have lower hydraulic conductivity. At the macroscopic viewpoint,increasing water content generally results in an increased ability to break down clay aggre-gates and to eliminate inter-aggregate pores (Mitchell et al., 1965; Benson and Daniel, 1990;Garcia-Bengochea et al., 1979). In addition, the clay particles are more uniformly dispersedand the macropores become constricted and tortuous (Barden, 1974). At the microscale,increasing water content result in reorientation of clay particles and reduction in the size of

Table 3Results of the three replicate measurements of hydraulic conductivity and their averages at

various water contents and compactive efforts

Hydraulic conductivity (cm/s)

Compactive Measurement Measurement Measurementefforts

Watercontent

(%) no. 1 no. 2 no. 3 Average

Modified Proctor 10.12 1.16 × 10−7 1.42 × 10−7 1.34 × 10−7 1.31 × 10−7

12.06 5.91 × 10−8 5.21 × 10−8 6.02 × 10−8 5.71 × 10−8

14.02 3.19 × 10−8 2.84 × 10−8 3.44 × 10−8 3.16 × 10−8

15.92 4.01 × 10−8 3.36 × 10−8 3.45 × 10−8 3.61 × 10−8

18.12 5.72 × 10−8 6.52 × 10−8 5.52 × 10−8 5.92 × 10−8

20.03 1.09 × 10−7 8.40 × 10−8 8.02 × 10−8 9.11 × 10−8

Standard Proctor 12.03 4.66 × 10−7 5.43 × 10−7 4.34 × 10−7 4.81 × 10−7

14.10 2.59 × 10−7 3.01 × 10−7 2.99 × 10−7 2.86 × 10−7

16.13 7.71 × 10−8 7.48 × 10−8 8.10 × 10−8 7.76 × 10−8

18.06 6.13 × 10−8 5.94 × 10−8 5.45 × 10−8 5.84 × 10−8

20.11 7.49 × 10−8 7.30 × 10−8 6.79 × 10−8 7.19 × 10−8

22.16 9.93 × 10−8 9.60 × 10−8 1.26 × 10−7 1.07 × 10−7

Reduced Proctor 14.03 1.25 × 10−6 1.11 × 10−6 9.52 × 10−7 1.10 × 10−6

16.20 5.77 × 10−7 5.34 × 10−7 6.49 × 10−7 5.87 × 10−7

18.10 1.48 × 10−7 1.20 × 10−7 1.10 × 10−7 1.26 × 10−7

19.99 1.37 × 10−7 1.12 × 10−7 1.14 × 10−7 1.21 × 10−7

22.13 1.52 × 10−7 1.55 × 10−7 1.90 × 10−7 1.66 × 10−7

24.09 2.49 × 10−7 2.40 × 10−7 3.03 × 10−7 2.64 × 10−7

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Figure 3. Hydraulic conductivity versus molding water content.

interparticle pores (Lambe, 1954; Acar and Oliveri, 1989). The hydraulic conductivity isthe key parameter for most soil liners and covers, thus great attention is generally focusedon ensuring that low hydraulic conductivity is achieved. Therefore, it is usually preferredto compact the soil wet of optimum.

For use as waste containment barrier, compacted clay liners should have a hydraulicconductivity of at least 1 × 10−7 cm/s. Figure 3 shows that both the modified and standardcompaction efforts cause hydraulic conductivity less than 1 × 10−7 cm/s for a wide rangeof water content. But reduced proctor compactive effort does not yield minimum hydraulicconductivity of 1 × 10−7 cm/s. The minimum hydraulic conductivity and correspondingwater content at various compactive efforts is presented in Table 4. In the case of each com-pactive effort the minimum hydraulic conductivity is obtained at water content of slightly(2–2.5%) wet of optimum water content. This is similar to that reported for compacted clays(Benson and Daniel, 1990; Elsbury et al., 1990).

Compaction mold permeameter is known to cause sidewall leakage between sampleand compaction mold. Thus, it overestimates the hydraulic conductivities of the samplestested. Therefore, the actual hydraulic conductivities are expected to be lower. On the otherhand, there is another fact that the field hydraulic conductivities are usually higher thanthat found in the laboratory. Thus, a better judgment on the hydraulic conductivity of soilliners could be achieved based upon in situ experiments. However, Reades et al. (1990)

Table 4Minimum hydraulic conductivity and corresponding water content at various

compactive efforts

Water content (%) atMinimum hydraulic minimum hydraulic Optimum water

Compactive efforts conductivity (cm/s) conductivity content (%)

Modified Proctor 3.05 × 10−8 14.6 12.4Standard Proctor 5.82 × 10−8 18.1 15.8Reduced Proctor 1.15 × 10−7 19.5 17.4

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demonstrated that similar hydraulic conductivity values could be obtained between labo-ratory hydraulic conductivity testing of samples collected in tubes and full-scale lysimetertesting of the clay liner. The work of Johnson et al. (1990) also indicated that with well-controlled field compaction the ratio between field and laboratory measured hydraulic con-ductivity would be between 0.6 and 2, i.e. effectively equal. The works of these two authorsdemonstrate that laboratory testing can be a useful means of measuring hydraulic conduc-tivity and the expense of large-scale field hydraulic conductivity testing may not always benecessary.

4.4 Volumetric Shrinkage

Compacted cylindrical specimens are used to determine shrinkage strain of the residualsoil. Cylindrical specimens shrink into smaller cylinders but do not crack. The result ofvolumetric shrinkage test is presented in Figure 4. Test results indicate that shrinkageincreases with increasing compaction water content and independent of compactive effort,which is also the case in the study performed by Daniel and Wu (1993). Each of the threedifferent compactive efforts show little volume change behavior of less than 4%, which istypical maximum permissible limit for compacted clay liner.

4.5 Unconfined Compressive Strength

The result of unconfined compression test against molding water content is shown inFigure 5. The strength of compacted soil decreases with the increase of molding watercontent. The same fact was observed by Seed and Chan (1959). The strength greatly de-creased for the samples compacted at wet of optimum water content. Compactive effort hasalso a great influence on soil strength. At lower water contents, unconfined compressivestress decreases with decreasing compactive effort. But no clear trend is noticed at higherwater contents.

Compacted soils used for waste containment barrier must have adequate strength forstability. The bearing stress acts on the barrier system depends on the height of landfill andthe unit weight of waste. Thus, to date, the minimum required strength of soil used for CCL

Figure 4. Volumetric shrinkage strain versus molding water content.

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Figure 5. Unconfined compression strength versus molding water content.

is not specified. Test result shows (Figure 5) that the soil possesses higher strength than therecommended minimum strength of 200 kPa for all compactive efforts at water contents ofabout 16% or less.

From the above discussions it is clear that the primary factors (such as hydraulicconductivity, strength, and shrinkage potential) controlling the performance of clay linersare greatly influenced by molding water content. In order to minimize hydraulic conductivityit is usually preferable to compact the soil at wet of optimum water content. However, themolding water content should not too high. Otherwise, the strength will be too low. Inaddition, the soil will show high volumetric shrinkage potential. Thus, it is very importantto specify the acceptable range of water contents within which the compacted soil willexhibit hydraulic conductivity ≤1×10−7 cm/s, volumetric shrinkage ≤4% and unconfinedcompressive strength ≥200 kPa. The acceptable range of water content is given in Table 5.Only the modified Proctor test meets the acceptable limits.

Table 5Acceptable range of water content

Range of water Range of watercontent (%) within Range of water content (%) within

which hydraulic content (%) within which unconfined AcceptableCompactive conductivity which volumetric compressive strength range of

efforts ≤1 × 10−7cm/s shrinkage ≤4% ≥200 kPa water (%)

Proctor 10.7 to 20.2 0 to 14.3 <10 to 17.1 10.7 to 14.3modifiedcompaction

Proctor 15.6 to 21.8 0 to 15 <12 to 16.9 —standardcompaction

Reduced — 0 to 15.2 <14 to 16 —compaction

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Moreover, the free swell index of the soil is 23%, indicates low to moderate swellingpotential. Soils with low swelling potential are suitable for compacted soil liner (McBeanet al., 1995). In addition, the soil possesses a cation exchange capacity of 5.3 meq/100 g ofsoil. Though its CEC does not meet the minimum requirement, modified compactive effortcould significantly increase its fluid retention capacity.

5. Conclusions

Based on the results presented in this paper, the following conclusions can be made:

1. The basic properties (liquid & plastic limit, % fines, % clay content, etc.) of the soilsatisfy the basic requirements as a hydraulic barrier material.

2. The activity (PI/%C) value of the soil is lower than bentonite (activity 1.5 to 7),which indicates that this soil would likely be less affected by waste chemicals andalso less susceptible to shrinkage.

3. The free swell index for sedimentary residual soil is 23%. Therefore, the swelling po-tential is low to moderate and it indicates that the soil is suitable for the constructionof hydraulic barrier/compacted clay liners.

4. The required hydraulic conductivity (≤1 × 10−7 cm/s) and unconfined compressivestrength (≥200 kPa) can be achieved by applying modified compaction energy at ashort range of water content of around ±2% from the optimum water content. Thevolumetric shrinkage strain can be also kept/restricted below 4%.

5. The sedimentary residual soil can be considered a suitable material for waste con-tainment barrier/compacted soil liner in landfills. However, extensive field studiesare required to ascertain this laboratory observation. Careful consideration must begiven to mixing, compaction, and lift thickness so that macroscopic defects leads tohigh field hydraulic conductivity could be avoided.

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