Avaliação de métodos de campo para a determinação de condutividade hidráulica em meios saturados e não saturados

AUTOR(ES)
DATA DE PUBLICAÇÃO

2010

RESUMO

The determination of the hydraulic conductivity of saturated insaturated media for hydrogeologic research is a frequent activity, to academic studies and for practical works. This hydrodynamic parameter is determined by in situ measures, for the insaturated zone the concentric rings and open end hole methodologies are applied and for the saturated zone the slug and bail test is commonly used. To the determination of the hydraulic conductivity the field data attainment can be carried out by different ways and the treatment of these data can be developed by the use of different equations, generating contradictory results and some times results totally disconnected to the reality of the studied aquifers systems. This research looked for the evaluation of the methodologies for field data acquisition and the best solution for the data set for estimation of hydraulic conductivity in different media (sandy-gravel material, structured tropical soils, broken and granite and siltstone saprolite), in the vadose and in the saturated zone. It was developed in situ infiltration tests to the saturated and not saturated zones in soils and monitoring wells in the Federal District and south Tocantins State regions (Brazil). The data were obtained by hand and automatically (with a pressure transducer advice) and were treated by Microsoft Excel and by hydrogeology commercial software using four mathematical solutions: the Yield Method, Hvorslev, Bouwer &Rice and Cooper et al. For the not saturated zone it was observed that the structured of soils and bioturbation are basic factors in the control of the hydraulic conductivity. The differences in soil types and in different horizons of the same soil profile are due to the texture, grain size and compaction of the different materials. For the saturated zone the different methods for determining the hydraulic conductivity, can result in contrasts over 100 times. By the results of this research, it was observed that the Yield Method can be applied to answer questions where the constructive or descriptive parameters of the well are not known. However, the results must be evaluated with care, because this equation tends to overestimate the hydraulic conductivity values. The results of the Slug type test added to the evaluation of the results of the in situ infiltration test and to the physical characteristics of the studied media, lead to consider that the data treated by the Hvorslev method indicate hydraulic conductivity values next to the waited for the studied materials. The results show that the type Slug Test can be carried out by manual form, without necessarily making use of a pressure transducer device, since some special care are considered as the repetition of the experiment when the maximum rise are not well measured and to evaluate the time intervals between each measure (in an approximately logarithmic scale of the drawdown versus time). The studies developed in this work show that the introduction of a water volume in the well is more convenient than the use of a slug for rising of the water level. This procedure is viable in cases where the well penetrates only one reduced section of the saturated zone, facilitates the repetition of the test with successively larger volumes and allows to more easily eliminate the well constructive effect on the results of hydraulic conductivity.

ASSUNTO(S)

hidrogeologia geografia física geociencias

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