Abstract The rock mass deformation modulus, Erm, is an input parameter for most numerical modeling to verify the deformation behavior of rocks due to rock engineering activities within/on it. Among the most common methodologies used for estimating this parameter, empirical correlations based on rock mass classification schemes (e.g., RQD, RMR, GSI, and Q) stand out the most, principally because of their low cost when compared to the other methods. Herein, the main correlations used in practice are evaluated and comparted for 48 different rock quality scenarios, previously characterized and classified according to rock mass classification systems. The results obtained by each of the empirical correlations demonstrated that normalized correlations, that is, based on the ratio of the rock mass and intact rock modulus, Erm/Ei, underestimate the Erm values when compared to those results obtained from not-normalized correlations in the scenarios of better quality rock masses. For poor quality rock mass scenarios, both non-normalized and normalized correlation presented similar results. The correlations proposed by Hoek and Diederichs (2006) and Galera et al. (2007) estimated more central Erm values when compared to the other correlations, for all quality scenarios, while the Mitri et al. (1994) and Sonmez et al. (2006) methods estimated most high and low values of Erm, respectively.

Abstract Sequence stratigraphy is a method that unravels the evolution of sedimentation through time and space within sedimentary basins. Nowadays, the exploration and production of natural resources generated by or related to sedimentary processes depend on constructing a chronostratigraphic framework to identify sequences of distinct hierarchies. In clastic and carbonate successions, exploratory studies focus on higher-rank sequences to evaluate the potential of natural resources and to make discoveries. Conversely, lower-rank (i.e. high-frequency) sequences characterize and highlight the spatial and temporal occurrence of natural resource deposits and heterogeneities, necessary for optimizing production. For instance, high-resolution sequence stratigraphic surfaces may indicate the location of placer deposits or coal seams. In the petroleum industry, high-resolution sequence stratigraphy is applied in reservoir zonation and characterization, which are the stratigraphic essence of 3D geological and fluid flow models. Thus, this methodology can guide reservoir management, forecast and optimize production, and increase the ultimate recovery factor. Recent technological innovations such as virtual outcrop models and Ground Penetration Radar have promoted a significant advance in the visualization of surfaces and stacking patterns, making stratigraphic analysis more accurate and efficient than the traditional use of analogs.

RESUMO Um estudo na sub-bacia hidrográfica do rio das Cobras foi realizado com o objetivo de avaliar as características morfométricas e o perfil longitudinal da bacia hidrográfica, como ferramenta de planejamento na locação de barragens subterrâneas. Os parâmetros morfométricos - coeficiente de compacidade, fator forma, densidade de drenagem e índice de circularidade - foram determinados. Também foi realizado o perfil de equilíbrio a fim de compreender a dinâmica de erosão e a disposição na sub-bacia estudada. Os resultados demonstraram que a sub-bacia do rio das Cobras possui forte caráter alongado, baixa densidade de drenagem e altas taxas de escoamento superficial para as áreas aluvionares. O perfil de equilíbrio indicou que o médio curso (18 km, trecho 2) da sub-bacia tem anomalia de primeira ordem com susceptibilidade a processos erosivos ao longo deste trecho. O segmento baixo curso (10 km, trecho 3) também possui anomalia de primeira ordem; porém, com tendência de agradação de material sedimentar (pacote sedimentar maior), advindo do médio curso. O médio curso da sub-bacia tem potencial para a construção de barragens subterrâneas submersíveis; já no baixo curso, recomenda-se a construção de barragens subterrâneas submersas. Os parâmetros morfométricos físicos não devem ser analisados isoladamente, mas integrados a outros aspectos de qualidade das águas superficiais e subterrâneas, área de recarga e demanda social ou produtiva da sub-bacia.

ABSTRACT A study was carried out in the sub-basin of the River Cobras with the aim of evaluating the morphometric characteristics and longitudinal profile of the river basin as a tool for planning the location of underground dams. Morphometric parameters - compactness coefficient, form factor, drainage density and circularity index - were determined. An equilibrium profile was also performed in order to understand the dynamics of erosion and disposition in the sub-basin under study. The results showed that the River Cobras sub-basin is strongly elongated, with low drainage density and high rates of runoff in alluvial areas. The equilibrium profile indicated that the middle course (18 km, stretch 2) of the sub-basin includes a first-order anomaly and is susceptible to erosive processes along this stretch. The lower course (10 km, stretch 3) also has a first order anomaly; however, with a tendency to favour the aggregation of sedimentary material (larger sedimentary bundle) coming from the middle course. The middle course of the sub-basin has potential for the construction of submersible underground dams; whereas in the lower course, the construction of submerged underground dams is recommended. The physical morphometric parameters should not be analysed in isolation, but together with other aspects of surface- and groundwater quality, the recharge area and the social or production demand on the sub-basin.

RESUMO Os métodos de investigação convencionais para alocação e manejo de barragens subterrâneas requerem ações invasivas no interior da estrutura investigadas, fornecendo apenas informações pontuais para pequenos volumes. Já, a aplicação de técnica de detecção não invasiva como, por exemplo, o Ground Penetrating Radar (GPR), possibilita investigar e explorar o sub-superficie sem destruir a estrutura. Com o objetivo de avaliar a inclusão da técnica Ground Penetrating Radar para estudos de alocação e monitoramento de barragens subterrânea no semiárido brasileiro, realizou-se a aquisição de perfil com Ground-Penetrating Radar no corpo aluvionar na sub-bacia do riacho Pau Lavrado, região Sertão Central de Lajes, Estado do Rio Grande do Norte do Brasil. O dados de registro do perfil Ground-Penetrating Radar foram adquiridos ao longo do trecho do corpo aluvionar selecionado, processado no software Reflex 5 e exportadas para o software Opendetec 4.4.0, obtendo-se um modelo virtual 3D do corpo aluvionar. A análise do perfil Ground-Penetrating Radar com modelagem 3D do corpo aluvionar indicaram as irregularidades do embasamento cristalino e da superfície topográfica externa (solo). A interpretação do perfil GPR do corpo aluvionar permitiu a alocação precisa da barragem subterrânea, aumentando a sua área de acumulação hídrica com custo construtivo reduzido devido à escolha de locais com menores pacotes sedimentares.

ABSTRACT The conventional method monitoring and adequateness of underground dams requires invasive investigatory actions with in their interior structure and only provides specific information for small volumes. On the contrary, application of non-invasive sensing techniques, such as ground penetrating radar (GPR), makes it possible to investigate and explore underground without affecting their structure. A GRP 3D profile was acquired with the aim to allot and monitor an underground dam in the Brazilian semiarid region in the alluvial sub-watershed of the Riacho Pau Lavrado in the Sertão Central de Lajes region of the state of Rio Grande do Norte in Brazil. The GPR profile records were acquired along an alluvial section, processed using the Reflex 5 software and exported into the Opendetec 4.4.0 software in order to obtain a virtual 3D model. The GPR 3D profile of the alluvial deposits shows irregularities of the crystalline basement and external topographical surface (soil). The interpretation of the alluvial GPR profile allows precise adequateness of the underground dam, which supports an increase in the area of hydric accumulation and promotes low-cost building due to the allocation selected with minor sedimentation.

RESUMO A qualidade da água de um rio dependente de vários fatores, incluindo a origem e quantidade de escoamento e a formação geologia dos solos ao longo do fluxo. Objetivou-se avaliar a origem e os mecanismos controladores da entrada dos íons e, consequentemente, da qualidade da água na sub-bacia do rio das Cobras, RN. Foram selecionados 13 açudes, sendo 3 no rio principal e 10 entre os afluentes, abrangendo toda a área e litologias da sub-bacia. As amostras foram coletadas em duas épocas distintas (final dos períodos secos e chuvosos) nos anos hidrológicos de 2009 e 2010, totalizando 4 momentos de coleta. Analisou-se o comportamento espacial e sazonal da qualidade da água na sub-bacia utilizando o diagrama de Piper e a origem dos íons pelo diagrama de Gibbs e razão molar. Constatou-se que em relação aos íons, predominam águas sódicas em 82% e águas bicarbonatadas 76% (cátions e ânions), respectivamente. Os resultados obtidos sugerem que o principal mecanismo controlador da salindiade está relacionado a interação das partículas coloidais (sedimentos orgânicos e minerais) com os íons dissolvidos na água. Também não se observou indícios de contaminação antrópica na área, tendo por base a análise de nitratos e nitritos.

ABSTRACT Stream water quality is dependent on many factors, including the source and quantity of the streamflow and the types of geology and soil along the path of the stream. This study aims to evaluate the origin and the mechanisms controlling the input of ions that effect surface water quality in the sub -basin of the Rio das Cobras, Rio Grande do Norte state, Northeastern Brazil. Thirteen ponds were identified for study: three in the main river and ten in the tributaries between, thus covering the whole area and lithology of the sub -basin. The samples were collected at two different times (late dry and rainy periods) in the hydrological years 2009 and 2010, equating to total of four collection times. We analyzed the spatial and seasonal behavior of water quality in the sub-basin, using Piper diagrams, and analyzed the source of the ions using Guibbs diagram and molar ratios. With respect to ions, we found that water predominate in 82% sodium and 76% bicarbonate water (cations and anions, respectively). The main salinity control mechanism was related to the interaction of the colloidal particles (minerals and organic sediment) with the ions dissolved in water. Based on the analysis of nitrates and nitrites there was no evidence of contamination from anthropogenic sources.