Solid Waste Technology & Management (Christensen/Solid Waste Technology & Management) || Landfilling: Geotechnology

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<ul><li><p>P1: JYSc10-04 JWBK458-Christensen September 3, 2010 21:5 Printer: Yet to come</p><p>10.4Landfilling: Geotechnology</p><p>R. Kerry Rowe</p><p>Queens University, Kingston, Ontario, Canada</p><p>Jamie F. VanGulckArktis Solutions Inc., Yellowknife, Northwest Territories, Canada</p><p>The geotechnical properties of waste are strongly influenced by its type. From a geotechnical perspective, waste canbe classified into two main groups. The first is soil-like waste, which is defined as particulate material for which theprinciples of soil mechanics are applicable. Examples of soil-like waste include excavated soil, road construction debris,and incineration residue (i.e. slag, ash, dust). The second is nonsoil-like waste, which includes material for which theprinciples of soil mechanics may have limited applicability, but have been used in describing waste behaviour. Nonsoil-likewaste may include municipal solid waste (MSW), some industrial waste, bulky waste, green waste, and residues frommechanical-biological treated waste. It is desirable during the design of landfill facilities to have details of the mechanical,hydraulic, and geotechnical properties of the disposed waste. Such information is necessary for proper investigationsinto issues such as landfill stability, settlement behaviour, and the design of landfill engineered components (i.e. barriersystem, collection system).</p><p>This chapter provides a summary of reported nonsoil-like waste parameters, specifically municipal solid waste, suchas unit weight, shear strength, hydraulic conductivity, settlement parameters, and dynamic stability values taken fromliterature. For each parameter, the chapter discusses factors influencing their value, methods of determination, valuesreported in the literature, and relevance to engineering design. Additionally, a summary of landfill failures and lessonslearned from these case histories is provided.</p><p>10.4.1 Geotechnical Classification of Waste</p><p>Classification and analysis of soil-like waste for geotechnical properties should be performed in accordance with con-ventional soil mechanics principles (Konig and Jessberger, 1997). Caution must be exercised in the interpretation of theresults and their implications for design because certain soil-like waste may produce geotechnical properties that cannot</p><p>Solid Waste Technology &amp; Management Edited by Thomas H. Christensen 2011 Blackwell Publishing Ltd. ISBN: 978-1-405-17517-3</p></li><li><p>P1: JYSc10-04 JWBK458-Christensen September 3, 2010 21:5 Printer: Yet to come</p><p>Landfilling: Geotechnology 735</p><p>Table 10.4.1 Classification proposed by Konig and Jessberger (1997) for material class analysis of waste materials.Reproduced with permission from Waste mechanics. Report of subcommittee 3, ISMMFE Technical Committee TC5 onEnvironmental Geotechnics, by Konig, D. and Jessberger, H.L, pp. 3576. (1997) Ruhr-Universitat, Bochum, Germany.</p><p>Analytical steps Material classes</p><p>Step 1: Sorting the material classes from total waste sample Bulky components, paper, cardboard Soft synthetics Hard synthetics Metals Minerals Wood Organics SludgeRemainder 120 mm</p><p>Step 2: Particle size distribution for remainder 120 mm. Distinguish ata minimum between three broad size fractions</p><p> 8 mm 840 mm 40120 mm</p><p>Step 3: Identification and description of each material class Geometry of waste components Grain Stick, fibre Foil-like Box</p><p> Water content Organic content</p><p>be fully explained based on the theory of soil mechanics. Information on the composition of waste can be obtained by anaudit of incoming waste to a landfill or by analysing already landfilled waste in test pits or borings.</p><p>Fassett et al. (1994) stated that the determination of engineering properties of nonsoil-like waste (specifically MSW)is problematic due to:</p><p> Widely variable properties resulting from the inconsistent and heterogeneous composition of the waste. Difficulty of obtaining representative samples of a sufficient size. Erratic nature of the waste particles which makes sampling and testing difficult. Change in waste properties with time and location (due to biodegradation and physicochemical decay processes).</p><p>A waste audit can be made on a large quantity of waste that enters a landfill facility. Konig and Jessberger (1997)proposed the following description of the waste (Table 10.4.1) including the following three steps: (1) sorting of materialclasses from total waste sample (bulky components like paper and cardboard, soft synthetics, hard synthetics, metals,minerals, wood, organics, sludge), (2) determining the particle size distribution (at least three size fractions) for theremainder from the sorting procedure 120 mm, and (3) identification and description of each material class with respectto particle geometry, water content, and content of organics. The organic content may be classified according to therelative ease of breakdown over time (Landva and Clark, 1990), as summarized in Table 10.4.2.</p><p>For existing landfills, samples are obtained by borings and excavation of pits. But it is difficult or expensive to obtain alarge number of samples. Landva and Clark (1990) summarized their experiences in drilling and sampling within landfillsas follows:</p><p> The use of split spoon samplers of various diameters in municipal waste recovered very little material. Auger drilling is most suitable for sampling all types of municipal waste above and below the water table. The best</p><p>overall continuous auger with respect to production rate and quality and size for the sample was a solid-stem 130-mmauger (140-mm bit). The range of auger diameters used varied between 100 and 230 mm in diameter. A reasonably</p></li><li><p>P1: JYSc10-04 JWBK458-Christensen September 3, 2010 21:5 Printer: Yet to come</p><p>736 Solid Waste Technology &amp; Management</p><p>Table 10.4.2 Classification of the biodegradability of waste (adapted from Landva and Clark, 1990).</p><p>Class Examples</p><p>1. Organics(a) Putrescible (monomers and low-resistance polymers,</p><p>readily biodegradable)Food wasteGarden wasteAnimal wasteMaterial contaminated by such waste</p><p>(b) Nonputrescible (highly resistant polymers, slowlybiodegradable)</p><p>PaperWooda</p><p>TextilesLeathera</p><p>Plastica, rubbera</p><p>Paint, oil, grease, chemicals, organic sludge2. Inorganic</p><p>(a) Degradable Metals (corrodible to varying degrees)a</p><p>(b) Nondegradable Glassa, ceramicsa</p><p>Mineral soil, rubbleTailings, slimesAshConcrete, masonry (construction debris)</p><p>aMay contain numerous void-forming constituents that will affect the geotechnical behaviour of the waste fill.</p><p>heavy drill rig is required to penetrate or displace problematic materials such as wood, tires, rock, concrete blocks,and steel objects.</p><p> Test pits can be used in most landfills but are limited to depths of about 4 m and generally it is not feasible to excavatebelow the ground water level.</p><p>10.4.2 Density and Unit Weight of Waste</p><p> Definitions: Density and Unit Weight of WasteThere are two densities commonly used in landfill engineering, they are the in-place density and total average landfilldensity.</p><p>The in-place density () is defined as the mass of waste (Mw, includes mass of refuse and moisture) per unit volumeof waste (Vw, includes mass of refuse, moisture, and voids).</p><p> = MwVw</p><p>The in-place density has units [M/L3], typically reported as kg/m3 or t/m3. The in-place density will depend on thecomposition of the waste and can be used as an assessment of the degree of compaction.</p><p>The total average landfill density (av) is equal to the mass of waste plus cover material (including the moisturecontained in both) per unit volume of landfill and has the same units as in-place density.</p><p>av = Mw + McVw + Vc</p><p>This is the density used in stability calculations for loads on collection pipes, foundation, etc.</p></li><li><p>P1: JYSc10-04 JWBK458-Christensen September 3, 2010 21:5 Printer: Yet to come</p><p>Landfilling: Geotechnology 737</p><p>The bulk unit weight of the waste ( ) can be calculated by multiplying the total average landfill density by gravitationalacceleration constant (g):</p><p> = avg</p><p>The bulk unit weight has units [Force/L3], typically reported as kN/m3.The bulk unit weight of waste has a reported range of 1 to 19 kN/m3. The average landfill density can be calculated</p><p>by dividing the unit weight by gravitational acceleration constant (9.81 m/s2), which results in a density range of 102 to1936 kg/m3 or 0.10 to 1.93 t/m3 (note: 1 kN = 1000 kg/m/s2; 1000 kg = 1 t).</p><p> Influencing Factors: Density and Unit WeightThe density or unit weight of landfill waste is highly variable and is dependent on many factors such as:</p><p> Waste composition: MSW containing relatively greater proportions of dense material such as metal, glass or rock,would be expected to have a higher unit weight than MSW comprised primarily of less dense material such as organicmatter or textiles (Landva and Clark 1990; Manassero et al. 1996). Similarly, the frequency of placement and thethickness of relatively dense daily cover soil will influence the bulk unit weight of the waste mass. Additionally, wastecomposition changes due to decomposition. Thus, the unit weight may change depending on the age of the waste andtherefore may have different values with time and location within the landfill.</p><p> Degree of compaction: An increase in the compacted effort applied to the waste increases the unit weight of thewaste (e.g. Fassett et al. 1994; Van Impe 1994).</p><p> Moisture content: The larger the percentage of fluid (e.g. water or leachate) in the waste, the greater the bulk unitweight. The moisture content of MSW may be highly variable, with reported values between 10 and 100 %, dependon factors such as the organic content and age of the waste (Knochenmus et al. 1998). Other factors that may influencethe moisture content include: (1) landfill operations, such as leachate recirculation which inject leachate back into thewaste to promote rapid waste stabilization, (2) composition of the waste, (3) local climatic conditions, (4) percolationthrough the landfill cap/cover, and (5) effectiveness of the leachate collection and removal systems.</p><p> Applied stress: The unit weight of waste generally increases with depth due to the compression and consolidationunder the overburden stress (Knochenmus et al., 1998).</p><p> Methods of Determination: Density and Unit Weight of WasteThe most common and reliable method of evaluating the in-situ unit weight of landfilled MSW is through the excavationof test pits (Gachet et al. 1998). This method involves the excavation of waste using a mechanical shovel (backhoe). Thewaste is then weighed, and the excavated volume is deduced by either (1) lining the excavation with an impermeablematerial (PVC, HDPE) and filling with a known volume of water, or (2) surveying the volume of the cut. Detailedspecifications and analysis of the advantages and disadvantages of this and other density determination methods may befound in Gachet et al. (1998). Other techniques that have been employed include indirect methods such as core and augerdrilling, and direct methods, such as -adsorption, microgravimeter, and penetrodensitometer (Gachet et al. 1998). Somestudies have used test fills (e.g. Marques et al. 1998) and large-scale laboratory methods (e.g. Powrie and Beaven 1999)to obtain the unit weight of waste.</p><p>Other indirect methods for density determination involve surveying landfill volume and weight of incoming wasteand cover material, and measuring the unit weight of individual components of the waste and making an estimate of theoverall unit weight by using percentages of each component (Landva and Clark 1990; Qian et al. 2002). Oweis and Khera(1990) provide values for unit weight of individual waste components in municipal landfills. Landva and Clark (1990)also provide a summary of typical refuse composition and corresponding dry and saturated unit weights. Fassett et al.(1994) suggested the least reliable values are computed using indirect methods of determination.</p></li><li><p>P1: JYSc10-04 JWBK458-Christensen September 3, 2010 21:5 Printer: Yet to come</p><p>738 Solid Waste Technology &amp; Management</p><p>Table 10.4.3 Summary of density/unit weight of landfilled waste.</p><p>Bulk unit weight(kN/m3)</p><p>Density(tonne/m3) Source</p><p>Refuse landfill:Refuse to soil over ratio: 2:1 to 10:1</p><p>9.013.2 0.911.34 Landva and Clark (1986)a</p><p>For 6:1 refuse to daily cover soil 7.2 0.73 EMCON Associates (1989)a</p><p>Municipal refuse: Oweis and Khera (1990)b</p><p>Poor compactionModerate to good compactionGood to excellent compactionBaled wasteShredded and compacted</p><p></p><p>5.510.56.410.5</p><p>0.280.470.470.720.720.960.561.070.651.07</p><p>Incinerator residue Oweis and Khera (1990)b</p><p>Poorly burntIntermediately burntWell burntAshes</p><p>7.211.812.6</p><p>6.48.2</p><p>0.731.201.28</p><p>0.650.83Densified MSW (heavy tamping) 10 1.02 Van Impe (1994)MSW Fassett et al. (1994)Poor compactionModerate compactionGood compaction</p><p>3958</p><p>9.010.5</p><p>0.310.910.510.810.911.07</p><p>MSW Gachet et al. (1998)c</p><p>Zero compactionSlight compactionMean compactionExtreme compactionNot important</p><p></p><p>1.017.3</p><p>0.100.810.240.660.360.780.</p><p>MSW Machado Santos et al. (1998)Compacted waste, heavy cover 1419 1.431.94MSW Marques et al. (1998)Compacted to varying degreesLoose (precompaction)</p><p></p><p>0.710.960.370.67</p><p>aCompiled based on summaries by Sharma et al. (1990), modified from Qian et al. (2002).bModified from a summary compiled by Oweis and Khera (1990).cSummary of various reported studies (approximately 200 values).</p><p> Reported Values: Density and Unit Weight of WasteA summary of literature reported waste unit weight is provided in Table 10.4.3. The range of reported values is indicativeof the heterogeneous nature of waste. The great degree of scatter indicates the importance of site-specific unit weightdeterminations for any landfill design analyses. Note the importance of compactive effort on waste unit weight in thereported values. It should also be noted that these values do not reflect the increase in unit weight that can occur with theuptake of additional moisture due to heavy rain, leachate recirculation, or leachate mounding.</p><p> Relevance to Design: Density and Unit Weight of WasteThe weight of the waste material within a landfill typically provides the main driving force in slope stability analyses, anda reliable estimate of the unit weight is necessary for an accurate assessment of stability (discussed in Section 10.4.3).Likewise, the weight of waste provides the main component of overburden pressure giving rise to settlement (discussedin Section 10.4.5). Due to the heterogeneity of MSW and the change in parameters with time (due to physicochemical</p></li><li><p>P1: JYSc10-04 JWBK458-Christensen September 3, 2010 21:5 Printer: Yet to come</p><p>Landfilling: Geotechnology 739</p><p>processes), an accurate assessment of unit weight is often difficult, time-consuming and costly, and therefore the unitweight is often estimated for stability and settlement analyses. Acknowledging the difficulty in measuring this parameter,Manassero et al. (1996) recommended that testing be undertaken to assess the unit weight prior to undertaking stabilityor se...</p></li></ul>


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