On the resonance effect by dynamic soil–structure interaction: a revelation study

The present study makes an attempt to investigate the soil–structure resonance effects on a structure based on dynamic soil–structure interaction (SSI) methodology by direct method configuration using 2D finite element method (FEM). The investigation has been focused on the numerical application for the four soil–structure models particularly adjusted to be in resonance. These models have been established by single homogenous soil layers with alternating thicknesses of 0, 25, 50, 75 m and shear wave velocities of 300, 600, 900 m/s-a midrise reinforced concrete structure with a six-story and a three-bay that rests on the ground surface with the corresponding width of 1,400 m. The substructure has been modeled by plane strain. A common strong ground motion record, 1940 El Centro Earthquake, has been used as the dynamic excitation of time history analysis, and the amplitudes, shear forces and moments affecting on the structure have been computed under resonance. The applicability and accuracy of the FEM modeling to the fundamental period of soils have been confirmed by the site response analysis of SHAKE. The results indicate that the resonance effect on the structure becomes prominent by soil amplification with the increased soil layer thickness. Even though the soil layer has good engineering characteristics, the ground story of the structure under resonance is found to suffer from the larger soil layer thicknesses. The rate of increment in shear forces is more pronounced on midstory of the structure, which may contribute to the explanation of the heavily damage on the midrise buildings subjected to earthquake. Presumably, the estimated moment ratios could represent the factor of safeties that are excessively high due to the resonance condition. The findings obtained in this study clearly demonstrate the importance of the resonance effect of SSI on the structure and can be beneficial for gaining an insight into code provisions against resonance.     

Use of geothermal methods in outlining deep groundwater flow systems in Paleozoic interior basins of Brazil

Results of regional-scale geothermal studies are presented, providing new insights into the characteristics of deep groundwater flow systems in the Paleozoic sedimentary basins in the Amazon, Paraná and Parnaíba regions of Brazil. The study makes use mainly of bottom-hole temperature data sets for oil wells, the depths of which vary from 1,000 to 4,000 m. The techniques employed in data analysis have allowed identification of non-linear features in vertical distributions of temperature, produced by deep groundwater flows in the study area. According to the results obtained, vertical velocities of subsurface flows are found to fall in the range 10^?10 to 10^?9 m/s, while the horizontal velocities are significantly higher, of the order 10^?8 m/s. Identification of large-scale down flows has allowed inferences as to the existence of lateral movements of groundwater. The basins in the Amazon region are found to be characterized by widespread down flow of groundwater, implying the existence of distributed recharge systems operating on regional scales. There is a systematic decrease in horizontal velocities along the direction from west to east. This feature is considered indicative of gravity driven flows induced by episodes of uplift, since Miocene times, in the Andean region.     

Spatial scale variability in shoot density and epiphytic leaves of Posidonia oceanica on Kerkennah Island (Tunisia) in relation to current tide effects

A study was undertaken of the patterns of spatial variability, epiphytic biomass and distribution of epiphytic fauna and flora of Posidonia oceanica. Samples were taken at four stations located approximately 4 km apart, exposed to different current conditions. Stations A and B, situated near the Oued Mimoun tidal channel with its relatively strong bi‐directional flows, were affected by high current tide. The other two stations, North Oued Mimoun (L1) and South Oued Mimoun (L2), were located further from the channel, in low current tide conditions. Sampling was conducted in the Attaya area of Kerkennah Island (Tunisia) in August 2009 at depths between 2 and 3 m, with the results indicating differences among the stations. Shoot density decreased when exposed to high levels of hydrodynamic activity generated by current tides whereas the epiphytic biomass of P. oceanica leaves decreased at sheltered stations located far from the channel. Epiphytic algae such as Heterokontophyta, Rhodophyta and Chlorophyta, and epiphytic fauna represented by Bryozoa, Hydrozoa, Annelida, Porifera and Tunicata, dominated the epiphytic assemblages and were abundant at the station most exposed to high current tide hydrodynamics. Cyanobacteria, however, were dominant in stations exposed to low current tide.     

Uptake of hazardous elements by spring onion (<Emphasis Type="Italic">Allium fistulosum</Emphasis> L.) from soil irrigated with different types of water and possible health risk

Bio-concentration of elements such as Mo, As, Se, Fe, Cu, Zn, Ni and Pb was analyzed in spring onion (Allium fistulosum L.) in three different locations of central Punjab, Pakistan. At location GW, relatively low level of hazardous elements was found in spring onion, suggesting that groundwater is a safe source of water for irrigating food crops. The pH of soil at wastewater irrigation was found less acidic (pH 7.4) than the other sites. The range of concentration in the different samples of spring onion was as follows: 6.15–8.16 mg kg^?1 for Mo, 2.77–4.28 mg kg^?1 for As, 0.395–0.705 mg kg^?1 for Se, 36.73–48.17 mg kg^?1 for Fe, 10.58–16.26 mg kg^?1 for Cu, 28.87–39.79 mg kg^?1 for Zn, 6.66–8.75 mg kg^?1 for Ni and 4.33–6.09 mg kg^?1 for Pb, respectively. High bio-concentration of Zn (15.37) from soil to spring onion was found at canal water irrigated location. The estimated daily intake of metal for spring onion was less, but the health risk index was higher than 1 for Mo, As, Cu, Pb and Ni, respectively. This was due to higher proportion of spring onion in diet, which consequently increased the health risk index for metals. Therefore, it is recommended to avoid growing vegetables in untreated urban and rural wastewater containing elevated amounts of metals.     

Characteristic Study of the Boundary Layer Parameters over the Arabian Sea and the Bay of Bengal Using the QuikSCAT Dataset

The marine atmospheric boundary layer （MABL） plays a vital role in the transport of momentum and heat from the surface of the ocean into the atmosphere. A detailed study on the MABL characteristics was carried out using high-resolution surface-wind data as measured by the QuikSCAT （Quick scatterometer） satellite. Spatial variations in the surface wind, frictional velocity, roughness parameter and drag coefficient for the different seasons were studied. The surface wind was strong during the southwest monsoon season due to the modulation induced by the Low Level Jetstream. The drag coefficient was larger during this season, due to the strong winds and was lower during the winter months. The spatial variations in the frictional velocity over the seas was small during the post-monsoon season （-0.2 m s^-1）. The maximum spatial variation in the frictional velocity was found over the south Arabian Sea （0.3 to 0.5 m s^-1） during the southwest monsoon period, followed by the pre-monsoon over the Bay of Bengal （0.1 to 0.25 m s^-1）. The mean wind-stress curl during the winter was positive over the equatorial region, with a maximum value of 1.5×10^-7 N m^-3, but on either side of the equatorial belt, a negative wind-stress curl dominated. The area average of the frictional velocity and drag coefficient over the Arabian Sea and Bay of Bengal were also studied. The values of frictional velocity shows a variability that is similar to the intraseasonal oscillation （ISO） and this was confirmed via wavelet analysis. In the case of the drag coefficient, the prominent oscillations were ISO and quasi-biweekly mode （QBM）. The interrelationship between the drag coefficient and the frictional velocity with wind speed in both the Arabian Sea and the Bay of Bengal was also studied.     

Instrumental Neutron Activation Analysis of Estuarine Sediment as a Proposed Reference Material for Environmental Studies

The International Atomic Energy Agency (IAEA) Marine Environmental Studies Laboratory (MEL) organised an intercomparison exercise, through its Analytical Quality Control Services (AQCS), for the determination of trace elements in estuarine sediment IAEA-405, well suited for the characterisation of sediments. The instrumental neutron activation analysis technique (INAA) was developed using a 27 kW low power research reactor. Forty elements in the sediment were determined with a measurement precision varying from 1.8% to 12.3%. IAEA reference materials SL-1 and SD-M-2/TM were analysed throughout this work as quality assurance samples.     

Oxygen isotopic fractionation between oxygen of different sites in hydroxyl-bearing silicate minerals

A method has been developed for extraction of hydroxyl oxygen from hydroxyl-bearing silicate minerals for oxygen isotopic analysis.The δO¹⁸ of oxygen of the OH groups is significantly different from that in the rest of the mineral structure. The isotopic fractionation between the two types of sites has the potential to be a sensitive geothermometer.Several δO¹⁸ values were obtained for oxygen of the OH attached to different silicate structures as well as for two muscovite samples with quantitatively estimated different temperatures of formation.The 1000 ln α (mineral-OH) values ranged from 5.2%. for muscovite to about 12.6%. for kaolinite and chlorite.     

Palygorskite from cave sediments: case study from Wadi Haqil,United Arab Emirates

The x-ray powder diffraction identification of clay minerals both in bulk samples and in separated clay fraction confirmed the presence of palygorskite in samples of cave sediments from Wadi Haqil (the western slopes of Musandam Mountains; Ras Al-Khaimah Emirate, UAE). Samples contain quartz, gypsum, smectite, kaolinite, calcite, and palygorskite, some of them chlorite, illite, feldspars, and goethite. Calcite dominates in most samples; smectite prevails in clay fraction. After heating, the 001 reflection of chlorite shifts to higher diffraction angles and its intensity decreases; these features indicate that the chlorite represent a Fe-dominant species. Unit-cell dimensions of major phases as refined by the Rietveld method are in agreement with literature data. Chemical composition of palygorskite was derived from unit-cell dimensions as follows: MgO content is 11–14 wt% and Al₂O₃ 10–13 wt%. Clay mineralogy is only hard to ascertain from the scanning electron microscope (SEM) images even after being combined with the energy-dispersive spectrometer data. The SEM was also used to characterize gypsum grains; they often display flow deformation features. Studied cave sediments represent palygorskite-bearing weathering products and desert soils re-deposited from the cave surroundings by slope processes and wind and/or surface runoff. The mixture with other clay minerals, quartz, feldspars, etc. supports this interpretation. Fine-grained quartz fraction is probably wind-blown. Gypsum and calcite are the precipitates (crusts and/or cements), although gypsum can also be re-deposited from omnipresent gypsum-cemented surface sediments.     

Assessing groundwater storage in the Kairouan plain aquifer using a 3D lithology model (Central Tunisia)

The aquifer of the semi-arid Kairouan plain has been exploited for decades to supply the growing irrigated agriculture and the need of drinking water. In parallel, the major hydraulic works drastically changed the natural groundwater recharge processes. The continuous groundwater level drop observed since the 1970s naturally raises the question of groundwater storage sustainability. To date, hydrogeological studies focused on groundwater fluxes, but the total amount of groundwater stored in the aquifer system has never been fully estimated. This is the purpose of the present paper. A complete database of all available geological, hydrogeological and geophysical data was created to build a 3D lithology model. Then, the lithological units were combined with the hydraulic properties to estimate the groundwater storage. Over the 700 km² of the modelled area, the estimated storage in 2013 was around 18?×?10⁹ m³ (equivalent to 80 times the annual consumption of 2010) with a highly variable spatial distribution. In 45 years (1968–2013), 12% of the amount of groundwater stored in the aquifer has been depleted. According to these results, individual farms will face strong regional disparities for their access to groundwater in the near future.