DSpace Community:
http://hdl.handle.net/10174/14389
2024-03-28T17:27:29Z
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Preliminary Analysis of Slope Instability Processes Triggered in the Guilherme Creek Watershed (Nordeste Municipality, S. Miguel Island, Azores)
http://hdl.handle.net/10174/27453
Title: Preliminary Analysis of Slope Instability Processes Triggered in the Guilherme Creek Watershed (Nordeste Municipality, S. Miguel Island, Azores)
Authors: Maciel Amaral, Paulo; Marques, Rui T. F.; Duarte, Isabel M.R.; Pinho, António B.
Editors: Fernandes, Francisco; Malheiro, Ana; Chaminé, Helder I.
Abstract: The Nordeste Volcanic Complex is located in the NE sector of S. Miguel Island (Azores) and it is composed of geological formations with about 4 million years old, extremely weathered. This fact, allied to the steep slopes on the area, promotes the occurrence of slope instability phenomena. In particular, the Guilherme Creek watershed has a high recurrence of this type of geological hazard, mainly triggered by precipitation, which promotes a high density of landslides in the area. Considering as main objective the landslide susceptibility analysis in the Guilherme Creek watershed, using statistical/probabilistic methods, it is ongoing an inventory process of these phenomena in a GIS, based on the aerial photography interpretation and fieldwork. Currently, the inventory is concluded based on aerial photography from 1982 and orthorectified aerial photography from 1995 to 2005. In order to validate and update the landslide inventory produced in the office, fieldwork has been carried out using, besides more traditional techniques, a drone (DJI Phatom 4 PRO). This tool has allowed studying steep slopes, which would otherwise be impossible to access in an area with a high forest density and very steep slopes. Until now, 517 landslides have been identified in the study area, mainly belonging to slides and falls typologies.
2020-01-03T00:00:00Z
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Subsidence Hazard in Limestone Cavities: The Case of “Grutas da Moeda” (Fátima, Central Portugal)
http://hdl.handle.net/10174/27435
Title: Subsidence Hazard in Limestone Cavities: The Case of “Grutas da Moeda” (Fátima, Central Portugal)
Authors: Duarte, Isabel M. R.; Pinho, António B.; Lopes, Luís; Sábio, Ricardo; Jorge, Micael
Editors: Fernandes, Francisco; Malheiro, Ana; Chaminé, Helder I.
Abstract: “Grutas da Moeda” are natural touristic caves, located in the plateau of São Mamede, near Sanctuary of Fátima, in Portugal. They have been opened to the public since 1974, and receives about 75,000 visitors per year, from 76 nationalities. They are located in the “Maciço Calcário Estremenho”, composed by limestone deposits of the Middle Jurassic (Bathonian), corresponding to the Serra de Aire formation. The geological risk assessment is fundamental to guarantee the safety of its visitors and staff; therefore, it is intended to develop geotechnical monitoring methodologies in order to collect data to understand the risks that may be associated with this natural cavity and to identify critical areas of collapse. There are four main alignments (faults/joints), which assume parallelism with the development of the caves. The trend of the layers in the cave is approximately N30ºE; 17ºSE. In the year 2015, a geophysical study was carried out, using the 3D electrical resistivity method and, for one of the areas in particular, the georadar method. The georadar method allowed to map the anomalies corresponding to empty spaces that have been identified with the 3D electrical resistivity technique. This paper presents the results obtained, as well as proposals for geotechnical measures to mitigate the risk of collapse subsidence.
2020-01-03T00:00:00Z
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Residual Soils
http://hdl.handle.net/10174/24936
Title: Residual Soils
Authors: Duarte, Isabel M.R.; Rodrigues, Isabel M. R.
Editors: Bobrowsky, Peter T.; Marker, Brian
Abstract: 2018 Edition reference work entry "Synonyms: Alteration products; Lateritic soils; Saprolites; Weathering products Definition: Residual soil is the material resulting from the in situ weathering of the parent rock which has not been transported from its place of origin. Residual soils are distributed throughout many regions of the world, such as Africa, South Asia, Australia, Southeastern North America, Central and South America, and considerable regions of Europe. The largest areas and thicknesses of these soils occur normally in humid tropical regions, such as Brazil, Nigeria, South India, Singapore, and the Philippines. Characteristics: According to Duarte (2002), the diversity exhibited by the residual soils is due, not so much, to the lithology of the original rock, but mainly to external factors such as climate, topography, and vegetation cover; factors that provide distinctive weathering processes; and, consequently, distinctive weathering products – the residual soils. At the first International Conference on Tropical Residual Soils, it was proposed to divide such soils into..." This is a preview of subscription content, log in to check access Copyright information © Springer International Publishing AG 2018.
2018-01-01T00:00:00Z
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Influence of anisotropy on the mechanical properties of Baixo Alentejo flysch rocks (Portugal)
http://hdl.handle.net/10174/17370
Title: Influence of anisotropy on the mechanical properties of Baixo Alentejo flysch rocks (Portugal)
Authors: Pinho, António B.; Duarte, Isabel M.R.; Rosa, Francisco R.S.; Rodrigues-Carvalho, José A.
Editors: Hassani, Ferri; Hadjigeorgiou, John; Archibald, Jamie
Abstract: This paper aims to contribute to the knowledge of the mechanical properties of the shales and
greywackes which constitute the flysch-type deposits of the Baixo Alentejo Flysch Group, in the south of
Portugal. These formations are flysch-type deposits constituted by sequences of usually thick greywacke
beds alternating with thin shale beds, which include sometimes intercalations of conglomerate beds. All the
sedimentation of these flysch formations was controlled by tectonics. At the same time, should have
occurred along with the first Hercynian deformation phase, a low-grade metamorphic event (chlorite zone),
that affected these flysch deposits. This study highlights the influence of anisotropy and heterogeneity of
these flysch rocks on their physical and mechanical characteristics. The anisotropy verified in some
physical properties and on mechanical properties, due to the foliation makes difficult the sample
preparation for the laboratory tests. Besides, it induces a scattering of the properties values measured, as
for example, the strength and the deformability. The heterogeneity is related to the main features of these
geological formations, which are constituted mostly by thinly stratified greywackes and shale beds, which
sometimes may affect the results of the laboratory tests making them less representative. The study is made
by using both shales and greywackes that constitute these flysch-type deposits in order to evaluate their
geotechnical properties, mainly of the shales. Samples of these two rock materials, are tested accordingly a
laboratory testing programme, which includes which included mineralogical analysis (X-ray diffraction),
physical tests (bulk density, porosity, and void index) and mechanical tests (uniaxial compression, and
deformability tests).
2015-05-09T23:00:00Z