This work results from the application of geostatistical techniques on Standard Penetration Test (SPT) data to the geotechnical characterisation of an area with 44km² situated on the northeastern region of Fortaleza county, northeastern Brazil. The geotechnical characterization involved the following steps: the geotechnical databank development; the performance of the interpolation algorithms and application to the Digital Elevation Model (DEM); estimation and mapping the water table level with ordinary kriging and cokriging techniques; generation of a 3D surface geological model; geostatistical mapping the SPT maximum hard penetration surface; application of 3D geostatistical modeling techniques to SPT database providing bench estimates on blocks. The SPT estimated data were inserted and reclassified on the Geographical Information System based on the software ESRI ArcView 3.1 in order to produce the suggested foundation maps with references to SPT penetration limits.

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Recebido em 06 de junho de 2008; aceito em 15 de setembro de 2008 RESUMOMapas de curvas equipotenciais são obtidos a partir de poços de monitoramento espalhados pela região que se deseja representar. Estes mapas são elaborados a partir dos mais variados métodos de interpolação, porém nem sempre a densidade de informações de cota potenciométrica disponível é sufi ciente para a realização de uma boa estimativa. Nestes casos pode-se lançar mão da utilização de interpoladores mais complexos, como por exemplo, a cokrigagem ou a krigagem com deriva externa, que são métodos que utilizam mais de uma fonte de informações, complementares, para a interpolação de uma dada característica. Neste trabalho foram aplicadas a cokrigagem ordinária, a krigagem com deriva externa e a krigagem com deriva externa com correção do efeito de suavização para a elaboração do mapa potenciométrico de um aquífe-ro livre na porção NE da região metropolitana de Fortaleza, estado do Ceará. A cokrigagem ordinária, dos três métodos, é sem dúvida o mais trabalhoso e o que apresentou os piores resultados uma vez que a correlação entre a cota potenciométri-ca e a cota altimétrica diminuiu após as estimativas. A krigagem com deriva externa apresentou-se como uma técnica viá-vel e mais simples de ser aplicada que a cokrigagem ordinária além de ter apresentado melhores resultados uma vez que a correlação entre as duas informações não foi alterada signifi cativamente.Palavras-chave: geoestatística multivariada, cokrigagem, krigagem com deriva externa, efeito de suavização, mapa potenciométrico, hidrogeologia. ABSTRACTEquipotential maps are obtained from monitoring wells distributed over the study area. These maps can be built using several interpolation methods, nevertheless the available potentiometric information is not suffi cient to ensure good estimation for unsampled locations. In these cases one can use more complex interpolators such as normal cokriging and external drift kriging, with and without correction of the smoothing effect. These methods consider not only the variable to be estimated but also another correlated variable. Thus, we can use information coming from a secondary source to estimate the main variable. For instance, elevation is well correlated with potentiometric data and it is very easy to acquire over the study area. In this paper cokriging, kriging with external drift, and kriging with external drift after correcting the smoothing effect have been used for the preparation of the potentiometric map of a free aquifer in the NE part of Fortaleza City, Ceará State. Among the three tested methods cokriging gave the worst results because of the instability of the system of cokriging equations. Kriging with an external drift seems to be appropriate since it is simpler to implement than cokriging, and it depends on correlation of the secondary information with the variable to be estimated. Furthermore, kriging with external drift after correcting the smoothing effect did not improve the results because available information is not un...

This research was focused on weathering conditions regarding Banded Iron Formations (BIF) ore exploitation at Bonito Mine. The database is stemmed from an exhaustive drilling program at the mining site. Therefore, hundreds of iron ore samples were assayed for Fe2O3, SiO2, Al2O3, P and Mn grades, and qualitative geotechnical data such as weathering grades, physical ore type, voids, and coring depth levels were collected from drilling core samples. A previous petrographic study has shown that there are four BIF types: amphibolitic itabirites, martitic itabirites, hematitic itabirites, and magnetitic itabirites. In order to enhance this study, a multivariate model using geochemical and geotechnical data under a systemic approach was employed. This approach was conceived to account for the whole available information, both quantitative and qualitative, through the Correspondence Analysis and Cluster Analysis grounded appropriate methodology. This innovative strategy disclosed the presence of two groups of samples, denoted in the sequel Cluster 1 and Cluster 2. Cluster 1 is characterized by the Fe-poorer/High-Al BIF ores describing an association of magnetitic itabirites, martitic itabirites to amphibolitic itabirites which are conditioned to depths deeper than 70 meters and they usually stand as slightly weathered rocks or fresh rocks. Cluster 2 encompasses Fe-richer/Low-Al BIF ores composed of martitic, magnetitic and hematitic itabirites which are described as moderate to highly weathered porous friable ore materials. The proposed multivariate modeling strategy can deal with a wide range of miscellaneous geological issues.