Comportamento filtro-drenante de geotêxteis em barragens de rejeitos de mineração

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

The behaviour of tailing dams depends on their filtration and drainage systems. In this context, this dissertation aimed to study the behaviour of geotextiles in such systems. To accomplish that, field and laboratory tests were performed on the main variables related to the filtration mechanism. These tests allowed the characterization of the filtration process and the identification of the main agents of this process. The field investigations were made in tailing dams of iron and phosphate industries. In these investigations the flow condition was the main disturbing agent. The general geometry of the tailing dams, as well as the field properties of the materials, were studied. A geotextile specimen was exhumed from a drainage system of one of the tailing dams of the iron industry and was subjected to studies on the interaction with the tailings by assessing its impregnation level, grain size analyses of the particles entrapped in the geotextile and optical and electronic scanning microscopy. Twenty samples of the tailings were collected and representative samples were chosen for the laboratory filtration tests. Geotextiles with masses per unit area varying between 200 and 600 g/m2 were employed in the gradient ratio tests (GR) under pressure, being subjected to constant and varying hydraulic gradients. It was observed that the stresses applied at the top of the soil samples tended to reduce eventual heterogeneities observed at the beginning of the tests, being the stress of 200 kPa a threshold value for these variations. The tailings tested behaved as stable materials in all tests, being observed only localized migrations of particles in the regions close to the geotextile layer. The grain size analyses of the particles that piped through the geotextiles showed that only the soil fine fraction suffered the effects of the variation of hydraulic gradient, while the increments in normal stresses affected the passage of coarser particles thorough the geotextile. Post test microscopic analyses of the geotextiles showed large particles in the geotextile voids, which was corroborated by the grain size analyses of the entrapped particles. In general, the tailing-geotextile systems tested behaved in a stable manner, which was conflicting with some predictions by design criteria available in the literature. In this sense, the GRASTM was very effective to quantify the system behaviour and this value was always close to unity, which is a sign of system stability. Nevertheless, the other GR definitions, GRMod and GR3mm, were also important for the evaluation of the geotextile influence on the behaviour of the neighbouring soil regions. It is important to point out the relevance of the complementary studies carried out to understand the behaviour of the systems tested that included grain size analyses of the particles that piped through the geotextile as well as visual and microscopic investigations of the geotextiles at the end of the tests.

ASSUNTO(S)

ensaios de laboratório geotêxteis geotecnica filtração engenharia civil drenagem mecânica dos solos barragens de rejeitos

ACESSO AO ARTIGO

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