Alterações geomecânicas e mineralógicas de mistura solo-bentonita contaminada por lixiviado de aterro sanitário.

Abstract

Municipal Solid Waste Landfill leachate poses a high risk to the environment because of its high contamination potential. In landfills, the percolation of this contaminant is contained through the liner. However, the compacted clay liner can have its properties changed, because of the leachate's high degree of alteration, and it can lead to the liner failure. Therefore, it is necessary to understand the effects of leachate on the liner materials to ensure that this constructive element fulfills its functions of load support and contaminant containment. This thesis aims to identify changes in the shear strength of a soil-bentonite mixture subjected to different degrees of contamination by landfill leachate. The research experimental field was the Sanitary Landfill in Guarabira (Brazil), where leachate samples and samples of soils that composed the Landfill liner were collected. The soil and leachate samples were characterized and the soil mixture was contaminated by the addition of leachate in proportions of 5%, 12.5% , and 20% to the dry mass of the studied soil mixtures. The contaminated soil samples were submitted to consistency limit tests, compaction, energy dispersion X-ray spectroscopy, X-ray diffraction, and direct shear strength tests. The results obtained show that the increase in the percentage of leachate added to the soil mixtures, in dry mass, resulted in an increase in the liquidity limit and an increase in the plasticity index of the mixture, this behavior is justified by the high concentration of chemicals and compounds organics in the leachate, which results in flocculation of the material due to the reduction of the diffuse double layer of the soil. The optimum moisture content of the contaminated samples ranged between approximately 15% and 17% and the maximum dry bulk density ranged between 1.88 g/cm³ with the clean sample and 1.70 g/cm³ for the contaminated sample with a proportion of 20% leachate added to the dry mass. For a normal tension of 50 kPa, the increase in the percentage of leachate added to the soil mixture generated an increase in the soil shear strength of this mixture. For tensions above 200 kPa, the increase in the perce ength of the samples. In general, the percentage of leachate added to the soil samples in the chosen proportions, and following the proposed methodology, did not demonstrate significant effects on soil chemistry and mineralogy, although they changed the behavior of the consistency limits of the samples. On the other hand, the obtained model showed that the soil samples contaminated with leachate presented a tendency to reduce their shear strength with the increase of the applied normal stress, which can generate problems with the embankment Cells heightening.