tropical soils, bentonite, hydraulic conductivity, compatibility, barriers. / CONDUTIVIDADE HIDRÁULICA E COMPATIBILIDADE EM COMBINAÇÕES DE SOLO TROPICAL E BENTONITA PARA USO EM BARREIRAS

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

Barriers are key elements for the environmental protection in waste disposal sites. Additionally, compacted tropical soils have great potential to be used in these barriers, once some technical matters are correctly addressed, including low hydraulic conductivity and adequate compatibility to the disposed fluids. In this context, the bentonite addition in tropical soils could be an alternative to improve these and other technical properties. This dissertation involves an integrated laboratorial study of the hydraulic conductivity of mixtures a tropical soil sample and bentonite and also their compatibility previous to different chemical solutions. The bentonite proportions of 3, 6, 9 and 12% (dry weight) were investigated, as well as the tropical soil and bentonite samples. The experimental program can be divided in three different steps: (1) sample characterization, which to investigate the modifications in properties (geotechnical and physicochemical) imposed to the samples as the result of the bentonite addition; (2) assessment of the hydraulic conductivity using the triaxial test (flexible-wall permeameter), under the constant hydraulic head of 50 kPa and confining pressures of 20, 40 and 80 kPa; and (3) compatibility assessment of the studied samples some chemical solutions (HNO3 - pH 3; NaOH - pH 11; NaCl - 5g/l and ethanol), using the modified Atterberg and bentonite free-swelling determination. The characterization results showed important changes in the index properties of tropical soil, highlighting a great increase in the plasticity, CEC and free swelling as the result of the bentonite addition. The hydraulic conductivity, in turn, experimented significant decreasing as the proportions of bentonite and confining pressure increased. Already the compatibility results showed significantly decreased in the plasticity of the samples when subjected to chemical solutions, more relevant for the salt solution, but not negligible for the acidic, basic and organic solutions. The decrease of plasticity has showed to be greater for the higher proportions of bentonite, as the result of the ionic double layer contraction. Finally, the overall results recommend the bentonite addition for improving the quality of tropical soils, once the geotechnical criteria (shear strength and permeability) and compatibility are considered for the specific fluid to be disposed.

ASSUNTO(S)

solos tropicais, bentonita, condutividade hidráulica, compatibilidade, barreiras selantes. tropical soils, bentonite, hydraulic conductivity, compatibility, barriers. geotecnica

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