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201.
Damping of structures resting on flexible foundations is affected by soil-structure interaction in two ways: (1) the structure gains damping through energy dissipation in soil, and (2) the damping the structure would have on a rigid foundation is reduced. These effects are evaluated using two approaches: an energy consideration which is a simple but approximate approach, and the complex eigenvalue analysis which is mathematically accurate but uses damped, non-classical vibration modes. These two methods are compared and the accuracy of the more convenient energy approach is assessed. Examples of modal damping are given for rigid structures, buildings and towers. 相似文献
202.
Philippe Paillou Ahmed El Barkooky Aly Barakat Jean-Marie Malezieux Bruno Reynard Jean Dejax Essam Heggy 《Comptes Rendus Geoscience》2004,336(16):1491-1500
Using orbital imaging radar, we have detected a large number of circular structures in the southwestern Egyptian desert, covering more than 4500 km2 close to the Gilf Kebir plateau in sandstones of Upper Cretaceous. Fieldwork confirmed that it is a new impact crater field: 13 craters from 20 m to 1 km in diameter were studied. The impact origin is confirmed by the observation of shock-related structures, such as shatter cones and planar fractures in quartz grains of breccia. Considering the extension of the crater field, it was possibly created by several meteorites that broke up when entering the atmosphere. To cite this article: P. Paillou et al., C. R. Geoscience 336 (2004).
Résumé
À partir d'images satellites issues de systèmes radar, nous avons détecté un grand nombre de structures circulaires dans le Sud-Ouest du désert égyptien, s'étendant sur plus de 4500 km2 à l'est du plateau du Gilf Kebir, dans des grès du Crétacé supérieur. Une étude sur le terrain a permis de vérifier qu'il s'agit d'un champ d'impacts météoritiques jusque là inconnu : 13 structures, d'un diamètre compris entre 20 m et 1 km, ont été reconnues comme cratères d'impact. La présence d'un grand nombre de cônes de percussion et de brèches dans lesquelles des quartz choqués à structures planaires ont été observés confirment l'hypothèse de l'impact. Considérant l'extension du champ d'impact, il a probablement été créé par plusieurs météorites qui se sont fragmentées dans l'atmosphère terrestre. Pour citer cet article : P. Paillou et al., C. R. Geoscience 336 (2004). 相似文献203.
The survey of sedimentological and lithostratigraphic Liassic facies of the Todrha–Dades area (southwestern part of the central High Atlas) permits to establish new data on the Tagoudite formation. Its environment deposit and its micropalaeontological content are evidenced in relation with the geodynamic evolution of the High Atlas Basin during the Early Toarcian. To cite this article: M. Ettaki, E.H. Chellaï, C. R. Geoscience 337 (2005). 相似文献
204.
Laurent Pfister Gilles Drogue Abdelkhalak El Idrissi Jean-François Iffly Christelle Poirier Lucien Hoffmann 《Climatic change》2004,66(1-2):67-87
The spatial variability of observed trends in rainfall structure over the last 5 decades and its effects on the spatial variability of maximum daily water levels in the Grand-Duchy of Luxembourg (Europe) were investigated in 9 sub-basins of the Mosel river. Over the past 25 years, an increase in westerly atmospheric circulation types during winter months has caused an increase in winter rainfall totals, duration and intensity. More specifically, the spatial variability of trends having affected winter rainfall totals, duration and intensity have led to spatially varying positive trends in maximum daily water levels. Observed trends in rainfall characteristics and maximum daily water levels during winter show closely linked spatial patterns that are strongly related to the topography of the study area. 相似文献
205.
H. El Arabi J. Canrot B. Ouahhabi A. Charrire S. Kerchaoui 《Journal of African Earth Sciences》2004,39(3-5):393
A comparative study of the Middle Liassic series in the south western part of the Middle Atlas system leads to the definition of three new formations called Fellat 1, 2 and 3. They mainly involve gravity-flow deposits related to the breakup of the regional carbonate platform in a subsiding area, the Selloum Basin. The creation of this basin provides evidence for a rifting stage during the Carixian–Domerian interval, inducing the separation of the Selloum unit with respect to the Middle Atlasic trough and its possible connection with the High Atlasic sedimentary domain. 相似文献
206.
This paper reports on the results of a study conducted on tanks partially filled with water, representing tuned liquid dampers (TLD), subjected to both 1D and 2D horizontal excitations. The sloshing response of the water in the tank is characterized by the free surface motion, the resulting base shear force, and evaluation of the energy dissipated by the sloshing water. A 1D non‐linear flow model capable of simulating a TLD equipped with damping screens is employed to model a 2D TLD. Application of this particular model requires the assumption that the response is decoupled and can be treated as the summation of two independent 1D TLDs. Results from the non‐linear flow model are compared with the 2D experimental shake table test results leading to a validation of the decoupled response assumption. This attractive decoupled response property allows square and rectangular tanks to be used as 2D TLDs, which can simultaneously reduce the dynamic response of a structure in two perpendicular modes of vibration. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
207.
Geophysical survey to estimate the 3D sliding surface and the 4D evolution of the water pressure on part of a deep seated landslide 总被引:5,自引:0,他引:5
Geophysical surveys were conducted on the very unstable front part of the La Clapière landslide in the French Alps (Alpes Maritimes). The electrical resistivity survey was carried out to obtain, for the first time on this deep-seated landslide, 3D information on the slipping surface and the vertical drained faults. Moreover, we planned to follow within time (6 months) the evolution of the saturated zones (presence of gravitational water) and their percolation into the shearing zones. Our 4D results showed the importance of the complex water channelization within the slope and relation to geological discontinuities. 相似文献
208.
Mahmoud M. El Banna 《Environmental Geology》2006,49(5):645-652
Bathymetry of the seafloor in the area in front of Ras El Bar coast, the characters of the seafloor sediments and the effects
of protective structures on seafloor bathymetry were examined. Seafloor depths in front of Ras El Bar seawall ranged between
2 and 4 m. These depths, coupled with wave climate, result in waves breaking directly onto the wall and exerting high, dynamic
pressures on the area at the structure’s toe. The sandy seafloor in front of the wall has been scoured. Sea water has undermined
the wall causing removal of sediment, destabilization of its slope and the whole face of the wall has slipped. Toe protection
in the form of a rocky apron is required to prevent such damage. West of the seawall, the constructed breakwater system has
affected the bathymetry of the seafloor in the area. Shoaling and submerged spits have been formed in the shadow of each breakwater
unit. The gaps between the breakwater units have attained deep depths and steep slopes. Scours and steep slopes adjacent to
the head of the breakwater units have been recorded. Seaward of the breakwater system, deeper depths and gentle slopes characterize
the seafloor. Offshore–onshore current and sediment movements toward the northeast is inferred from the configuration of the
bottom contour lines. 相似文献
209.
Geoelectrical and hydrogeochemical studies for delineating seawater intrusion in the outlet of Wadi Ham, UAE 总被引:2,自引:0,他引:2
M. Sherif A. El Mahmoudi H. Garamoon A. Kacimov S. Akram A. Ebraheem A. Shetty 《Environmental Geology》2006,49(4):536-551
The Quaternary aquifer of Wadi Ham, UAE has been overexploited during the last two decades to meet the increasing water demands.
As a result, the dynamic balance between freshwater and seawater has been disturbed and the quality of the groundwater has
deteriorated. In this paper, a 2D earth resistivity survey was conducted in Wadi Ham in the area between Fujairah and Kalba
to delineate the seawater intrusion. Existing monitoring wells were used to measure the horizontal and vertical variations
in water salinity and thus to improve the interpretation of earth resistivity imaging data. Results of vertical electrical
soundings and chemical analyses of collected water samples were used to obtain an empirical relationship between the inferred
earth resistivity and the amount of total dissolved solids. This relationship was used along with the true resistivity sections
resulting from the inversion of 2D resistivity data to identify three zones of water-bearing formation (fresh, brackish, and
salt-water zones). Along the four 2D resistivity profiles, the depth to the fresh-brackish interface exceeded 50 m at the
western part of the area and was in the order of 10 m or less in the eastern side near the shoreline. Depth to the brackish-saline
water interface reached about 70 m in the western side and was in the order of 20 m in the eastern side. The thickness of
the fresh water zone decreases considerably in the farming areas toward Kalba and thus the degree of seawater intrusion increases. 相似文献
210.
Brooks B. Ellwood Jenaro L. García-Alcalde Ahmed El Hassani Jindrich Hladil Francisco M. Soto Montserrat Truyls-Massoni Karsten Weddige Leona Koptikova 《Tectonophysics》2006,418(1-2):31
One major difficulty in geology is high-resolution correlation among widely separated sections, especially in the Paleozoic where magnetostratigraphy polarity is not well established because rocks are often remagnetized, where critical biostratigraphic zonation may be poor or lacking, or where structural complexities make correlations very difficult. To address this problem, we have been using magnetostratigraphy susceptibility measurements. Here, we report our work from the Middle Devonian in Europe and North Africa. The Middle Devonian (Emsian–Eifelian) global boundary stratotype section and point (GSSP), located in the Eifel Hills, western Germany, was ratified by the International Subcommission on Stratigraphy in 1985, after careful evaluation of the biostratigraphy for this and many other sections. The boundary interval has been characterized using biostratigraphy, and the beginning of the Eifelian stage has been specifically defined by the first occurrence of the conodont Polygnathus costatus partitus. We have collected the Eifel Hills section for magnetic susceptibility (MS) measurement and here we establish it as the magnetostratotype for the Emsian–Eifelian stage boundary, by formally defining the magnetostratigraphy susceptibility for the section. We then collected, measured and compared the magnetostratotype to four other sections for which conodont biostratigraphy has been studied and where P. costatus partitus is present; two Emsian–Eifelian sections in Morocco and two sections in the Czech Republic (including the Emsian–Eifelian parastratotype). Finally, we have measured the MS for the El Puerto Creek section in the Cantabrian Mountains of Spain and identified the location of the Emsian–Eifelian boundary within the section based on MS comparison to the GSSP in conjunction with excellent biostratigraphic indicators, primarily brachiopods. While the conodont zonation in the El Puerto Creek section is poorly defined, we believe that the correspondence between the MS and biostratigraphy in the section allows the identification of the Emsian–Eifelian boundary. These results indicate that this method can be successfully applied to marine sequences where ambiguities in correlation exist. 相似文献