Influence of fly ash and quicklime addition on behaviour of municipal solid wastes

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Journal Article
Journal of Soils and Sediments, 2013, 13 (7), pp. 1201 - 1212
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Purpose: Many closed municipal solid waste landfill sites are near urban areas and there are high expectations to improve geotechnical properties of these sites for re-development. Construction on closed landfill sites is generally a challenging task due to complex behaviour of creep, settlement, high amount of moisture content and weak shear strength of waste. This study presents the experimental results for the use of fly ash and quicklime in improvement of the geotechnical properties of municipal solid wastes (MSW). Materials and methods: The waste materials were collected from a closed landfill in the southwest of Sydney. The samples were prepared by integrating MSW with a mixture of fly ash-quicklime with a ratio of 3:1 in percentages of 5, 10, 15 and 20 of fly ash by dry weight of the MSW. An array of experimental tests has been conducted on treated and untreated MSW samples including sieve analysis, Atterberg limits, compaction and consolidated-drained triaxial tests. Results and discussion: Results of this investigation showed a significant improvement in geotechnical properties of MSW. It has been found that by increasing fly ash-quicklime admixtures from 0 to 26.7 % (0 to 20 % fly ash), the internal friction angle increased from 29 to 39° and the cohesion intercept increased from 11 to 30 kPa. Under an effective confining pressure of 300 kPa, the peak strength, the brittleness index and the Young's modulus at failure increased from 600 to 1,150 kPa, 0.13 to 0.35 and 5.5 MPa to 28 MPa, by addition of 26.7 % fly ash-quicklime admixture, respectively. Moreover, the compression and the secondary compression indices decreased from 0.33 to 0.23 and 0.052 to 0.033, respectively. Conclusions: It is found that the chemical stabilisation effectively increases the compressive strength, the shear strength parameters, the stiffness and the brittleness index whilst decreases the settlement of the MSW layer. It will be beneficial and effective in re-development of closed landfill sites incorporating chemical treatments. The findings of this study may facilitate the calculations of the bearing capacity and settlement as well as the slope stability analysis of chemically treated closed landfill sites. © 2013 Springer-Verlag Berlin Heidelberg.
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