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Chen, Meixiang (College of Physical and Environmental Oceanography, Ocean University of China, Qingdao, Shandong, China) | Du, Ling (College of Physical and Environmental Oceanography, Ocean University of China, Qingdao, Shandong, China) | Zuo, Juncheng (Key Laboratory of Coastal Disaster and Defence, Ministry of Education, Hohai University, Nanjing, Jiangsu, China) | Chen, Changlin (College of Physical and Environmental Oceanography, Ocean University of China, Qingdao, Shandong, China, and Key Laboratory of Coastal Disaster and Defence, Ministry of Education, Hohai University, Nanjing, Jiangsu, China)
Characteristics of the tide and tidal currents on the northern Portuguese shelf are studied based on both station observation through May 13 to June 15, 2002 and a three-dimensional ECOM model simulation of the same period. Observation shows a surface intensified diurnal current in the upper layer of the area and a typically semidiurnal current in the layers below. Spectrum analysis suggests the summer wind stress in this area presents a strong diurnal fluctuation, which may induce a diurnal current in the sea surface. A three-dimensional model, ECOM, is implemented in this area for high-resolution tidal simulations for a homogeneous ocean. The four constituents M2 INTRODUCTION The northern Portuguese shelf (40ºN-42ºN) is characterized by a relatively regular topography and coastline. The shelf is flat, with an average width of about 45km and a bottom slope of about 5×10. The continental slope is well defined, with a slope of 0.1-0.2. The major topographic feature in this area is Porto Canyon and Aveiro Canyon, which affects the dynamic in the local sea area. The broad aspects of the shelf dynamics in this area can be related to the seasonal evolution of two major atmospheric systems, the Azores High and the Iceland Low (Woosteret al., 1976; Fiuza et al., 1982)., S2, K1 and O1, are included in the experiments. The simulated amplitudes and phases of surface height agree well with previous results. Vertical variation of tidal ellipse parameters suggests the different structure of semi-diurnal and diurnal tidal components, as well as differences in tidal circulation between the open sea and shelf sea. The QSCAT/NCEP Blended Ocean Winds is applied in the model to evaluate the influence of wind forcing. Result shows that the summer surface wind has little influence on the semi-diurnal tidal ellipses, but affects the diurnal tidal ellipses greatly, especially K1 component. The K1 tidal current shows surface intensification under the wind forcing, consistent with observation.
Ferreira Gomes, Luis M. (University of Beira Interior, Department of Civil Engineering, Covilha) | Pissarra Cavaleiro, Victor M. (University of Beira Interior, Department of Civil Engineering, Covilha) | Ladeira, Fernando L. (University of Aveiro, Department of Geosciences)
ABSTRACT: Geotechnical characteristics of claystones of Aveiro (Portugal) are presented. These formations generally have mechanical properties corresponding to the borderline between Soil Mechanics and Rock Mechanics. Some problems arise when foundations are excavated in those sediments. RESUMÉ: Dans ce travail sont presentees les caracteristiques geotechniques des argilolithes de la region de Aveiro (Portugal). Ces formations ont generalement, proprietes mecaniques qui correspondent à la frontiere entre la Mecanique des Sols et la Mecanique des Roches. Quelques problemes qui resultent des excavations pour les foundations dans ces sediments sont presente. ZUSAMMENFASSUNG: Der Text behandelt geotechnische Eigenschaften der Tonstein der Gegend von Aveiro (Portugal). Diese besitzen mechanische Eigenschaften die im Grenzbereich zwischen Bodenmechanik und Felsmechanik Iiegen. Einige Probleme bei der Ausschachtung von Fundamenten in diesen Sedimenten werden dargestellt. 1 INTRODUCTION This work was done in the Cretaceous claystones of Aveiro on the portuguese coast (Central Region of Portugal, SW Europe). This lithostratigraphic unit is designated by "sandstones and clays of Aveiro" (Teixeira and Zbyszewski, 1976) and "Vagos Clays" (Barbosa, 1981) and "Aveiro clays" (Ferreira Gomes, 1992). It occupies an area of about 100 Km2, with about 5 Km average width and 20 Km length; only 30 per cent outcrops and the rest is covered by recent sediments. The thickness of this geological unit ranges from 10 metres to the north to about 150 metres to the south. The sub-horizontal layers have 0.5 to 2.0 meters of thickness. The colour of these sediments is generally greenish, and sometimes reddish, greyish, dark, yellowish, bluish and whitish. This unit usually remains below the water table. 2 PHYSICAL PROPERTIES These claystones turn into residual soils after being immersed in water for some hours or days. The residual soils are classified as CH, CL and MH (Unified Soil Classification System, ASTM 1987). The "in situ" physical parameters of these sediments are presented in Table 1; the highest values of Wn and en correspond to the shallow unstressed sediments and the lowest values correspond to the massif not decompressed. Relationship for several physical parameters "in situ" are presented in figure 1. Geophysical studies such as electrical sounding and seismic refraction tests have been done. The values of resistivity (R) varied between 7 and 23 Ohm.m and more frequently between 13 and 18 Ohm.m. The seismic velocities (Vp), varied between 250 and 3280 mls. 3 STRENGTH AND DEFORMABILITY CHARACTERISTICS To determine the strength characteristics were done several tens of Windsor tests (Ladeira, 1988) in several points of the massif and in profiles of recent excavations. Using the average of penetration depths (P) in each place, values of P between 16 and 70 cm were obtained which correspond to uniaxial compressive strength (qu) between 67 and 2081 kPa (qu=1.33 × 106 p-2.33; Ladeira, 1988); the lowest values correspond to depths until 1 metre and the highest values to depths greather than 4 metres. Carbonate layers (0.3 to 0.5 metres of thickness) occur in some places associated with the claystones and they can reach 6000 kPa of uniaxial compressive strength. Samples were collected from some selected places which allowed the achievement of specimens with a height/diameter ratio (HID) of about 2.5; the specimens were submitted to uniaxial compressive strength tests (ISRM, 1978) are in concordance with the Windsor test results, varying approximately in the same limits. The natural moisture content (Wn) was determined in each specimen; the relationship between this parameter and the uniaxial compressive strength is presented in the figure 2.