Construction Problems on the Karstified Limestone Tuffs of Condeixa, Central Portugal: A Case Study     

M. Quinta Ferreira  J. L. Velho 《Geotechnical and Geological Engineering》2006,24(1):101-116

During the excavations for the foundations of a three storey building on the limestone tuffs of Condeixa, Central Portugal, a large dissolution fissure and smaller dissolution voids were found. Since the area has never been the subject of engineering geology investigation, it was decided to evaluate the risk associated with the construction of the building. These limestone tuffs were formed in a continental environment by the precipitation of calcite carried by the water coming from the large limestone body in the east. The precipitated calcite mixed with the terrigenous materials and around trunks and leaves of plants, originating a very heterogeneous and porous ground, which is characteristic of limestone tuffs. The study started with a detailed geological survey followed by a large number of destructive drillings, located essentially under the pad foundations. The results revealed several karstic cavities with serious problems for the building foundations and the structure, and many smaller dissolution cavities, often filled with clayey soils. The ground treatment solutions used included, dental cleaning, filling with concrete or granular material the dissolution structures accessible at the level of the foundation, reinforcement of the footing and the structure of the building and adding a continuous foundation beam to hold the foundations together. The cost of the engineering geology study, site investigation, ground treatment, and the reinforcement of the foundation and building, increased the total construction cost from 2%, at the design stage, to 4.8%.  相似文献   

The local structure of Ca-Na pyroxenes. I. XANES study at the Na K-edge     

Annibale Mottana  Takatoshi Murata  Ziyu Wu  Augusto Marcelli  Eleonora Paris 《Physics and Chemistry of Minerals》1997,24(7):500-509

 X-ray absorption Na K-edge spectra have been recorded on synthetic endmember jadeite and on a series of natural Ca-Na pyroxenes compositionally straddling the Jd-Di join. The C2/c members of the series are systematically different from the P2/n members. Differences can be interpreted and explained by comparing the experimental spectra with theoretical spectra. These have been calculated by the multiple-scattering formalism from the atomic positional parameters determined by single-crystal X-ray diffraction structure refinement on the same samples. In the full multiple scattering region of the spectra (1075 to 1090 eV) C-pyroxenes exhibit three features which reflect the 6-2 configuration of the O back-scattering atoms around the Na absorber located at the center of the cluster (site M2 of the jadeite structure). P-pyroxenes show more complicated spectra in which at least four (possibly five) features can be recognized; they reflect the two types of configuration (6-2 and 4-2-2) of O around Na in the two independent M2 and M21 eight-fold coordinated sites of the omphacite structure. A weak, sometimes poorly resolved peak at 1079 eV is diagnostic and discriminates C- from P-pyroxenes. The Garnet Ridge C2/c impure jadeite exhibits a spectrum which is intermediate between those of jadeite and omphacite. The Hedin-Lundqvist potential proves best for these insulating materials and allows multiple-scattering calculations agreeing well with experiments. Received: July 11, 1996/Revised, accepted: October 21, 1996  相似文献   

The organisation of fish assemblages in the regulated Lima basin, Northern Portugal     

Jos Maria Santos  Francisco Godinho  Maria Teresa Ferreira  Rui Cortes 《Limnologica》2004,34(3):224-235

In order to understand the structure of fish assemblages in the modified Lima basin (Northern Portugal), two distinct datasets concerning the presence and abundance of fish species were subjected to multivariate analysis. On the River Lima two types of flow modification are present within kilometres of one another: (a) a reduced and constant flow due to hypolimnetic release; and (b) an intense and irregular flow. A comparison of their influence on fish assemblages revealed a gradient of assemblage types from tributaries to main river sites. The latter were characterised by a strong dominance of cyprinids, particularly Iberian barbel (Barbus bocagei). The former harboured two kinds of fish assemblages: those closer to the river mouth were dominated by the cyprinids Iberian chub (Squalius carolitertii) and Iberian nase (Chondrostoma polylepis), which were also frequently present in the main river; while in those further upstream the predominant species was the brown trout (Salmo trutta). Although explanatory variables such as distance from source, altitude, substrate coarseness and width were the primary correlates of fish assemblage composition, dam construction and flow regulation also had a significant effect upon assemblage structure, particularly by: i) reducing the importance of migratory species; ii) constraining the presence of trout in the regulated segments; and iii) simplifying the community, especially in the case of the constant and reduced flow regime.  相似文献   

Problems associated with tourism development in Southern Africa: The case of Transfrontier Conservation Areas   总被引：2，自引：0，他引：2  

Sanette Ferreira 《GeoJournal》2004,60(3):301-310

Tourism in Southern Africa is synonymous with the wildlife safari. In the post-colonial era the establishment of so-called ‘peaceparks’ that straddle the borders of states has come to be seen as a key not only to increasing tourism in the Southern African region, but also to the modernizing of conservation policies and the development of rural economies. This paper focuses on the global and continental presence of transfrontier conservation areas, the link between conservation and tourism development, and the current factors that constrain and influence the realization of an ‘African Dream’ — ‘establishment of the greatest animal kingdom’. The unstable political situation in Zimbabwe and how this negatively affects wildlife conservation and tourism in the Gonarezhou part of the Greater Limpopo Transfrontier Park, serves as a case study. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Intermittent chaos in nonlinear wave–wave interactions in space plasmas     

Rodrigo A. Miranda  Erico L. Rempel  Abraham C.-L. Chian  Felix A. Borotto 《Journal of Atmospheric and Solar》2005,67(17-18):1852

There is increasing observational evidence of nonlinear wave–wave interactions in space and astrophysical plasmas. We first review a number of theoretical models of nonlinear wave–wave interactions which our group has developed in the past years. We next describe a nonlinear three-mode truncated model of Alfvén waves, involving resonant interactions of one linearly unstable mode and two linearly damped modes. We construct a bifurcation diagram for this three-wave model and investigate the phenomenon of intermittent chaos. The theoretical results presented in this paper can improve our understanding of intermittent time series frequently observed in space and astrophysical plasmas.  相似文献   

C-isotope Composition of Carbonates from Indravati Basin, India: Implications for Regional Stratigraphic Correlation     

Anil Maheshwari  A.N. Sial  Rajeeva Guhey  V.P. Ferreira 《Gondwana Research》2005,8(4):603-610

The Indravati Basin represents an unmetamorphosed and unfossiliferous sequence and shows a broad similarity in lithological association with other Purana Basins of Central India. The carbonates belonging to Indravati Basin have on average, moderately positive δ13 C values (up to +4.5). Numerous successions reported from other parts of world, show similar δ13 C values and contain evidence to suggest that the latest Mesoproterozoic to early Neoproterozoic period may represent an isotopically recognizable interval globally. The elevated δ13 C values of Indravati Basin are also correlatable with other Purana Basins in India including Upper Vindhyan Supergroup.  相似文献   

Coupling watersheds,estuaries and regional ocean through numerical modelling for Western Iberia: a novel methodology   总被引：1，自引：1，他引：0  

Francisco Campuzano  David Brito  Manuela Juliano  Rodrigo Fernandes  Hilda de Pablo  Ramiro Neves 《Ocean Dynamics》2016,66(12):1745-1756

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Glacial flood pulse effects on benthic fauna in equatorial high‐Andean streams          下载免费PDF全文

Sophie Cauvy‐Fraunié  Patricio Andino  Rodrigo Espinosa  Roger Calvez  Fabien Anthelme  Dean Jacobsen  Olivier Dangles 《水文研究》2014,28(6):3008-3017

Equatorial glacier‐fed streams present unique hydraulic patterns when compared to glacier‐fed observed in temperate regions as the main variability in discharge occurs on a daily basis. To assess how benthic fauna respond to these specific hydraulic conditions, we investigated the relationships between flow regime, hydraulic conditions (boundary Reynolds number, Re*), and macroinvertebrate communities (taxon richness and abundance) in a tropical glacier‐fed stream located in the high Ecuadorian Andes (> 4000 m). Both physical and biotic variables were measured under four discharge conditions (base‐flow and glacial flood pulses of various intensities), at 30 random points, in two sites whose hydraulic conditions were representative to those found in other streams of the study catchment. While daily glacial flood pulses significantly increased hydraulic stress in the benthic habitats (appearance of Re* > 2000), low stress areas still persisted even during extreme flood events (Re* < 500). In contrast to previous research in temperate glacier‐fed streams, taxon richness and abundance were not significantly affected by changes in hydraulic conditions induced by daily glacial flood pulses. However, we found that a few rare taxa, in particular rare ones, preferentially occurred in highly stressed hydraulic habitats. Monte‐Carlo simulations of benthic communities under glacial flood reduction scenarios predicted that taxon richness would be significantly reduced by the loss of high hydraulic stress habitats following glacier shrinking. This pioneer study on the relationship between hydraulic conditions and benthic diversity in an equatorial glacial stream evidenced unknown effects of climate change on singular yet endangered aquatic systems. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Crustal segments in the North Patagonian Massif,Patagonia: An integrated perspective based on Sm–Nd isotope systematics     

Carmen I. Martínez Dopico  Mónica G. López de Luchi  Augusto E. Rapalini  Ilka C. Kleinhanns 《Journal of South American Earth Sciences》2011,31(2-3):324-341

New insights on the Paleozoic evolution of the continental crust in the North Patagonian Massif are presented based on the analysis of Sm–Nd systematics. New evidence is presented to constrain tectonic models for the origin of Patagonia and its relations with the South American crustal blocks. Geologic, isotopic and tectonic characterization of the North Patagonian Massif and comparison of the Nd parameters lead us to conclude that: (1) The North Patagonian Massif is a crustal block with bulk crustal average ages between 2.1 and 1.6 Ga T_DM (Nd) and (2) At least three metamorphic episodes could be identified in the Paleozoic rocks of the North Patagonian Massif. In the northeastern corner, Famatinian metamorphism is widely identified. However field and petrographic evidence indicate a Middle to Late Cambrian metamorphism pre-dating the emplacement of the ca. 475 Ma granitoids. In the southwestern area, are apparent 425–420 Ma (?) and 380–360 Ma metamorphic peaks. The latter episode might have resulted from the collision of the Antonia terrane; and (3) Early Paleozoic magmatism in the northeastern area is coeval with the Famatinian arc. Nd isotopic compositions reveal that Ordovician magmatism was associated with attenuated crust. On the southwestern border, the first magmatic recycling record is Devonian. Nd data shows a step by step melting of different levels of the continental crust in the Late Palaeozoic. Between 330 and 295 Ma magmatism was likely the product of a crustal source with an average 1.5 Ga T_DM (Nd). Widespread magmatism represented by the 295–260 Ma granitoids involved a lower crustal mafic source, and continued with massive shallower-acid plutono volcanic complexes which might have recycled an upper crustal segment of the Proterozoic continental basement, resulting in a more felsic crust until the Triassic. (4) Sm–Nd parameters and detrital zircon age patterns of Early Paleozoic (meta)-sedimentary rocks from the North Patagonian Massif and those from the neighboring blocks, suggest crustal continuity between Eastern Sierras Pampeanas, southern Arequipa-Antofalla and the northeastern sector of the North Patagonian Massif by the Early Paleozoic. This evidence suggests that, at least, this corner of the North Patagonian Massif is not allochthonous to Gondwana. A Late Paleozoic frontal collision with the southwestern margin of Gondwana can be reconcilied in a para-autochthonous model including a rifting event from a similar or neighbouring position to its post-collision location. Possible Proterozoic or Early Paleozoic connections of the NPM with the Kalahari craton or the western Antartic blocks should be investigated.  相似文献   

Bismuth‐melt trails trapped in cassiterite–quartz veins     

Frederico Sousa Guimares  Alexandre Raphael Cabral  Bernd Lehmann  Francisco Javier Rios  Moiss Augusto Bacellar vila  Marco Paulo de Castro  Glucia Nascimento Queiroga 《地学学报》2019,31(4):358-365

Native bismuth in the form of metallic melt has been considered instrumental to the formation of some metallic ore deposits via a mechanism dubbed the “Liquid Bismuth Collector Model.” Here, we provide petrographical documentation of trail‐forming, μm‐sized blebs of native bismuth in cassiterite–quartz veins from the Santa Bárbara greisen Sn deposit in the Rondônia tin province of northern Brazil. These inclusions suggest the trapping of a Bi melt that took place during vein formation, in a mechanism similar to the entrapment of fluid inclusions.  相似文献