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71.
Kannan K. R. Iyer Jeevan Joseph Bruna C. F. L. Lopes D. N. Singh Alessandro Tarantino 《Geomechanics and Geoengineering》2018,13(2):88-103
The soil–water retention (SWR) characteristics of the clays play an important role in controlling their engineering behaviour, particularly, in the unsaturated state. Although, researchers have attempted to understand the water retention characteristics of the clays in their reconstituted or remoulded state, such studies are rare for the clays in their intact state. In this context, it becomes important to understand the influence of initial state of compaction, which would create different pore and fabric structure (viz., microstructure), on the water retention characteristics of the clays. With this in view, SWR behaviour was experimentally determined for the swelling clays (dried from different compaction states, viz., intact, reconstituted and remoulded) by employing Dewpoint PotentiaMeter (WP4C®). The changes in the pore size distribution of the clays at different stages of drying cycle were also studied by employing the Mercury Intrusion Porosimetry. The study reveals that the SWR curves for the intact and reconstituted specimens of the clays converge beyond a certain stage of drying. Also, a critical analysis of changes in the pore structure of the swelling clay specimens, during drying, indicates that the progressively deforming pore structure plays an important role in controlling its water retention characteristics to a great extent. 相似文献
72.
E.P. Nobi E. DilipanT. Thangaradjou K. SivakumarL. Kannan 《Estuarine, Coastal and Shelf Science》2010
Spatial distribution of metal concentrations in the surface sediment samples collected from 16 marine locations covering different coastal ecosystems such as mangroves, seagrasses, dead coral and sandy beaches of the Andaman islands, India was studied. pH, EC, sediment grain size and heavy metal (Al, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb and Zn) concentrations were determined and contamination factor (CF) and geo-accumulation index (Igeo) were calculated to understand the pollution status of the study area based on the background values. CF of different heavy metals has revealed that different metals have different levels of accumulation viz. Al: 0.01–0.22, Mg: 0.38–1.85, Fe: 0.06–0.74, Mn: 0.04–1.18, Cu: 0.18–2.93, Cr: 0.52–12.6, Zn: 0.3–1.39, Ni: 0.06–0.89, Pb: BDL–0.74, Co: 0.1–0.35 and Cd: 2.3–12.9. In general the metal concentration was less in these ecosystems when compared to similar ecosystems of mainland of India. Concentration of some metals like Cr and Cd was comparatively higher than the background values which is an important issue of concern to the coastal managers of the region. Spatial data on heavy metals, collected now, would help the coastal zone managers to identify the vulnerable sites and take remedial actions. 相似文献
73.
E. Saranathan R. Chandrasekaran D. Soosai Manickaraj M. Kannan 《Journal of the Indian Society of Remote Sensing》2011,39(1):107-115
Coastal zone is very dynamic, being the meeting place of land and sea water. The development in coastal area and subsequent
population growth have given rise to problems such as erosion, sedimentation, saltwater intrusion, degradation of natural
resources, etc. Satellite data has proved to be more appropriate for change detections quantifying and monitoring coastal
zones compared to conventional sources. An attempt is being made to elucidate the effect of shoreline changes with reference
to the spatial and field data observed along the Tharangampadi area. The base map was prepared on 1:50,000 scale for delineation
and identification of shoreline changes. The spatial variability of shoreline changes are studied using IRS 1B LISS-II 1991,
IRS 1C LISS-III 2004 and IRS P6 LISS-IV and IRS 1D PAN merge data 2006. The corresponding Survey of India toposheets of 1852,
1972 and survey and land record village map of 1918 also supplemented for this study. The kind and extent of shoreline changes
were investigated by using GPS during ground truth verification. The results are analyzed and presented in this paper. The
study results revealed that 180 m receding of the shoreline occurred in the past 155 years. 相似文献
74.
Abstract An examination of the temperature and current measurements from the NE Newfoundland Shelf indicates significant frontal variability at about a 7‐day period during the months of June‐September 1989. The oscillations recorded in 1989 appeared to have propagated into the region from the Labrador Shelf. Significant variability in the position of the shelf water/slope water front in the Bonavista area is also found between years and within the same year. Time series measurements also indicated that the transition from winter to summer conditions in the inshore region may be occurring during late July to early August. 相似文献
75.
Polybrominated diphenyl ethers (PBDEs) in marine sediments from industrialized bays of Korea 总被引:8,自引:0,他引:8
Concentrations of polybrominated diphenyl ethers (PBDEs) were determined in coastal sediments from heavily industrialized areas and major harbors in Korea. SummationPBDE(20) concentrations in sediments ranged from 2.03 to 2253ng/g dry weight. PBDE concentrations were higher at estuarine and inner bay locations close to industrial complexes and large harbors, indicating that the PBDE contamination in the sediments is due to local discharges from industrial complexes. Deca-BDE was the predominant congener and the concentrations were comparable to or higher than those reported from other countries. Non-parametric multidimensional scaling (MDS) ordination showed that deca-BDE technical mixture is the main source of PBDE contamination in Korean coastal waters, with minor contamination by octa-BDE product. This result is consistent with the consumption pattern of brominated flame-retardants (BFRs) in Korea. Significant correlations existed among BDEs 28, 47, 99, 100, 153, and 154; however, BDEs 183 and 209 showed little correlation with less highly brominated congeners. 相似文献
76.
77.
AbstractIn the present scenario, with much focus on sustainable development worldwide, Microbially Induced Calcite Precipitation (MICP) is a promising biological soil improvement technology. However, only very limited research is reported on the effectiveness of this technique in marine clays. This paper presents the salient features of an experimental study conducted on two typical marine clays stabilised by MICP. Effectiveness of the technique was evaluated through a series of one-dimensional consolidation tests, unconfined compression tests, and index property determinations. It is found that biostimulation approach is not effective in marine clay; bio-augmentation is needed for soil improvement. Bio-augmentation results in the reduction of liquid limit and plasticity index to about 29% and 47%, respectively for the marine clays. A comparable improvement in volume change behaviour is also observed. There is a marked increase in undrained shear strength, upto about 148%, of MICP treated marine clays at toughness limit water content. Curing is also found to have a significant role in soil improvement. The observed transition in the nature of the tested marine clays from that of fat clay to elastic silt suggests the potential of the proposed approach. An empirical equation is also proposed to predict compression index of MICP treated marine clays. 相似文献
78.
Wave-force coefficients of horizontal circular cylinders inclined with respect to the incoming waves, are studied numerically under conditions when the effects of flow separation are insignificant. The mathematical model is set in terms of a boundary-value problem for the velocity potential of the wave, which is formulated under the assumption of the linear diffraction theory, and solved numerically by the boundary element method. The numerical calculations are performed in the vertical plane, assuming uniform water depths in the direction along the axis of the cylinder. A first-order correction to the pressures is introduced to take account of the asymmetry of the velocity field around the cylinder when it is close to the plane bed. The correction procedure is found to be highly effective in computing the transverse forces for small gap ratios. The numerical results show that irrespective of the values of the gap ratio, the in-line forces are always sensitive to the wave directionality. The transverse forces, however, show sensitivity only for the smaller gap ratios. It is also shown that by accounting for the wave directionality effects in the wave kinematics only, the forces could be estimated to a certain extent by using the hydrodynamic force coefficients of inertia and lift corresponding to the normal waves. 相似文献
79.
80.
The satellite-derived moisture fields during different phases of two normal and poor monsoon years have been studied. Spectral
analysis was performed in different zones of the monsoon region to study the nature and modes of intraseasonal fluctuations
of lower layer moisture fields.
Seasonal mean fields of water vapour at low and middle layers show a dry anomaly over the Arabian subcontinent and a wet anomaly
over the Bay of Bengal during good monsoon years, while the anomalies show an opposite trend during the poor monsoon years.
The zonal and meridional propagation of low-frequency oscillations of moisture fields has also been examined. The southward
movement of low-frequency oscillations seems to be suppressed in good monsoon years as compared to the poor monsoon years,
whereas the northward movement of the same shows no particular difference. Fluctuations in the 30–50 day range are found shifted
to longer time-period side in the poor monsoon years. 相似文献