ABSTRACT. The influence of array configurations on the resolution of subsurface electrical resistivity tomography (ERT) imaging is one of the most discussed factors when it comes to resistivity data quality. Despite the flexibility of multichannel data acquisition systems nowdays, there is still a tendency to perform field observations with traditional arrays, mainly because they are already well understood configurations. The present work discusses a comparison between the results obtained with four electrode arrays (dipole dipole, pole dipole, Wenner-Schlumberger and Wenner) regarding the data resolution and the ability to identify the bedrock over the buried waste in the former Jockey Club landfill of Brasília, an important information to delimit the geometry of the mass of waste. Four electroresistivity lines were acquired with different electrode arrays, using the ERT technique, and models were calculated using the Res2DInv software, by the robust inversion method (L1-norm) and smooth-constrained least squares inversion (L2-norm). All arrangements produced models that presented the mass of waste with low resistivity, indicating strong influence of leachate. The best agreement with borehole information regarding the bedrock level was achieved with the dipole-dipole array. The L1-norm inversion provided more stable and smoothed models than the results obtained with the L2-norm method, also presenting smaller differences between the calculated and observed apparent resistivity.KEYWORDS: Electrical Resistivity Tomography; electrode arrays, waste disposal. RESUMO. A influência do arranjo eletródico na resolução de imageamento por tomografia de resistividade elétrica (TRE) da subsuperfície é um dos fatores mais discutidos quando se trata de qualidade de dados de resistividade. Apesar da flexibilidade dos sistemas multicanais de aquisição de dados, ainda há uma tendência em realizar observações em campo com arranjos tradicionais de eletrodos, devido a serem configurações já bem compreendidas. No presente trabalho, é discutida uma comparação entre os resultados obtidos a partir de quatro arranjos de eletrodos (dipolo-dipolo, polo-dipolo, Wenner-Schlumberger e Wenner) quanto a resolução dos dados e quanto a capacidade de identificar o embasamento rochoso sobre o maciço de resíduos no antigo aterro controlado do Jockey Clube de Brasília, uma importante informação para delimitar a geometria do maciço de resíduos. Foram adquiridas quatro linhas de eletrorresistividade com diferentes arranjos eletródicos, com a técnica TRE, e foram calculados modelos no software Res2DInv pelo método de inversão robusta (norma-L1) e de inversão de mínimos quadrados com restrição de suavidade (norma-L2). Todos os arranjos produziram modelos que apresentaram o maciço de resíduos com baixa resistividade, indicando forte influência de chorume. As melhores concordâncias com as informações de furos de sondagem foram alcançadas com o arranjo dipolo-dipolo. A inversão norma-L1 forneceu modelos mais estáveis e suavizados do que os resultados obtidos com a norma-L2, também apresentando diferenças menores entre a resistividade aparente calculada e medida.PALAVRAS-CHAVE: Tomografia de Resistividade Elétrica; arranjos eletródicos; disposição de resíduos.
The present work discusses the characterization of landfilled solid waste and saturated zones from the response of P and S-waves velocities (Vp and Vs), Poisson ratio (υ), Young’s modulus (E) and shear modulus (), obtained from velocity models in an area located in the former Jockey Clube Controlled Landfill. The obtained Vp values ranged from 231 to 1,160 m/s, while Vs values range from 124 to 449 m/s. The calculated υ ranged from 0.11 to 0.4, while and E ranged from 15 to 319 kPa and from 42 to 901 kPa, respectively. The values of and E indicate that the landfilled material is poorly competent. The combined interpretation of Vp, Vs and elastic parameters allowed the definition of three main layers in the surveyed area and their respective distance from soil surface, defined as: 1) Civil construction residual material, of around 10 meters thick; 2) A solid waste layer, of around 18 meters thick, marked as a lower Vs and higher υ interval, possibly associated with saturated material; and 3) below the depth of 28 meters, we estimate the natural landfill terrain, composed by the oxisol.
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