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1.
Kiseong Hyeong Inah Seo Hyun-Bok Lee Chan Min Yoo Sang-Bum Chi In Kwon Um 《Ocean Science Journal》2018,53(2):355-368
Radionuclide activities of 210Pb and 226Ra were measured to determine bioturbation coefficients (Db) in seven sediment cores from the Korean licensed block for polymetallic nodules in the Clarion–Clipperton Fracture Zone. Variability in Db is considered in the context of the sedimentological, geochemical, and geotechnical properties of the sediments. Db values in the studied cores were estimated using a steady-state diffusion model and varied over a wide range from 1.1 to 293 cm2/yr with corresponding mixing depths (L) of 26 to 144 cm. When excepting for spurious results obtained from cores where diffusive mixing does not apply, Db values range from 1.1 to 9.0 cm2/yr with corresponding mixing depths (L) of 26 to 63 cm. Such wide variability in Db and L values is exceptional in sites with water depths of ～5000 m and is attributed in this study to an uneven distribution of sediment layers with different shear strengths and total organic carbon (TOC) contents, caused by erosion events. The studied cores can be grouped into two categories based on lithologic associations: layers with high maximum shear strength (MSS) and low TOC content, showing a narrow range of Db values (1.1–9.0 cm2/yr); and layers with low MSS and high TOC content, yielding much higher Db values of over 30 cm2/yr. The distribution of different lithologies, and the resultant spatial variability in MSS and labile organic matter content, controls the presence and maximum burrowing depth of infauna by affecting their mobility and the availability of food. This study provides a unique case showing that shear strength, which relates to the degree of sediment consolidation, might be an important factor in controlling rates of bioturbation and sediment mixing depths. 相似文献
2.
Byung Sun Lee Sung-Ho Song Jin Sung Kim Jae Yeon Um Kyoungphile Nam 《Environmental Earth Sciences》2014,71(4):1521-1532
This study was conducted to identify the availability of coastal groundwater discharge (CGD), subsurface fluids flowing from inland through the coastal area to sea, as an alternative water resource for a large-scale reclaimed land. The behaviors of stable isotopes indicated that groundwater originated from inland precipitation and traveled as CGD along the coast line. Most of the groundwater samples collected from domestic wells installed along the old coast line were considered to be relatively fresh from the correlation analysis among chemical constituents. The average electrical conductivity (EC) values of the samples were identified as averaging 1,125–1,297 μS cm?1, corresponding to appropriate crop growth. A weathered-rock layer in a small catchment within the reclaimed land was proved to be a main CGD pathway, with electrical resistivity anomalies ranging from 7 to 14 Ω m. Five monitoring wells were placed in this catchment to delineate the occurrence of CGD. Long-term vertical EC profiling results for the monitoring wells indicated that CGD occurs within a depth of 30 m below the ground surface. Annual monitoring data for groundwater level and EC demonstrated that the water quality of CGD was improved by introducing fresh terrestrial groundwater. A remarkable improvement in water quality (EC decrease of 900–1,600 μS cm?1) of CGD was observed during the saline water pumping test that explains how CGD could be an alternative water resource for the reclaimed land. 相似文献
3.
Factors controlling typhoons and storm rain on the Korean Peninsula during the Little Ice Age 总被引：1，自引：0，他引：1
4.
Wooyong Um Jonathan P. Icenhower R. Jeffery Serne Cleveland J. Dodge Arokiasamy J. Francis 《Geochimica et cosmochimica acta》2010,74(4):1363-6031
The concentration and distribution of uranium (U) in sediment samples from three boreholes recovered near radioactive waste storage tanks at Hanford, Washington, USA, were determined in detail using bulk and micro-analytical techniques. The source of contamination was a plume that contained an estimated 7000 kg of dissolved U that seeped into the subsurface as a result of an accident that occurred during filling of tank BX-102. The desorption character and kinetics of U were also determined by experiment in order to assess the mobility of U in the vadose zone. Most samples contained too little moisture to obtain quantitative information on pore water compositions. Concentrations of U (and contaminant phosphate—P) in pore waters were therefore estimated by performing 1:1 sediment-to-water extractions and the data indicated concentrations of these elements were above that of uncontaminated “background” sediments. Further extraction of U by 8 N nitric acid indicated that a significant fraction of the total U is relatively immobile and may be sequestered in mobilization-resistant phases. Fine- and coarse-grained samples in sharp contact with one another were sub-sampled for further scrutiny and identification of U reservoirs. Segregation of the samples into their constituent size fractions coupled with microwave-assisted digestion of bulk samples showed that most of the U contamination was sequestered within the fine-grained fraction. Isotope exchange (233U) tests revealed that ∼51% to 63% of the U is labile, indicating that the remaining fund of U is locked up in mobilization-resistant phases. Analysis by Micro-X-ray Fluorescence and Micro-X-ray Absorption Near-Edge Spectroscopy (μ-XRF and μ-XANES) showed that U is primarily associated with Ca and is predominately U(VI). The spectra obtained on U-enriched “hot spots” using Time-Resolved Laser-Induced Fluorescence Spectroscopy (TRLIFS) provide strong evidence for uranophane-type [Ca(UO2)2(SiO3OH)2(H2O)5] and uranyl phosphate [Ca(UO2)2(PO4)2(H2O)10-12] phases. These data show that disseminated micro-precipitates can form in narrow pore spaces within the finer-grained matrix and that these objects are likely not restricted to lithic fragment environments. Uranium mobility may therefore be curtailed by precipitation of uranyl silicate and phosphate phases, with additional possible influence exerted by capillary barriers. Consequently, equilibrium-based desorption models that predict the concentrations and mobility of U in the subsurface matrix at Hanford are unnecessarily conservative. 相似文献
5.
In a probabilistic analysis of rock slope stability, the Monte Carlo simulation technique has been widely used to evaluate
the probability of slope failure. While the Monte Carlo simulation technique has many advantages, the technique requires complete
information of the random variables in stability analysis; however, in practice, it is difficult to obtain complete information
from a field investigation. The information on random variables is usually limited due to the restraints of sampling numbers.
This is why approximation methods have been proposed for reliability analyses. Approximation methods, such as the first-order
second-moment method and the point estimate method, require only the mean and standard deviation of the random variable; therefore,
it is easy to utilize when the information is limited. Usually, a single closed form of the formula for the evaluation of
the factor of safety is needed for an approximation method. However, the commonly used stability analysis method of wedge
failure is complicated and cumbersome and does not provide a simple equation for the evaluation of the factor of safety. Consequently,
the approximation method is not appropriate for wedge failure. In order to overcome this limitation, a simple equation, which
is obtained from the maximum likelihood estimation method for wedge failure, is utilized to calculate the probability of failure.
A simple equation for the direct estimation of the safety factors for wedge failure has been empirically derived from failed
and stable cases of slope, using the maximum likelihood estimation method. The developed technique has been applied to a practical
example, and the results from the developed technique were compared to the results from the Monte Carlo simulation technique. 相似文献
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7.
Chang H. Jung Junshik Um Ji Yi Lee Yong P. Kim 《Asia-Pacific Journal of Atmospheric Sciences》2013,49(5):625-634
This study characterizes the Ångstrom exponent for polydispersed aerosol size distributions. Under the assumption of a lognormal size distribution, the dependence of Ångstrom exponent on the size distribution and the refractive index with varying real and imaginary parts are determined. Further, the influence of coarse mode particles on the Ångstrom exponent is investigated quantitatively. The results show that the nuclei mode has less influence under the simulation conditions considered in this study. It is also shown that the refractive index is an important factor influencing the Ångstrom exponent. The effect of the coarse mode on the Ångstrom exponent computed with different aerosol number concentrations and as a function of a geometric standard deviation and a geometric mean diameter is tested. It is shown that the coarse mode is crucial for determining the Ångstrom exponent. 相似文献
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9.
Drilling at the site UBGH1-9, offshore Korea in 2007, revealed varied gas-hydrate saturation with depth and a wide variety of core litholgies, demonstrating how the variations in the lithology are linked with those in gas-hydrate saturation and morphology. Discrete excursions to low chlorinity values from in situ background chlorinity level occur between 63 and 151 mbsf. In this occurrence zone, gas-hydrate saturations estimated from the low chlorinity anomalies range up to 63.5% of pore volume with an average of 9.9% and do not show a clear depth-dependent trend. Sedimentary facies analysis based on grain-size distribution and sedimentary structures revealed nine sediment facies which mainly represent hemipelagic muds and fine- to medium-grained turbidites. According to the sedimentary facies distribution, the core sediments are divided into three facies associations (FA): FA I (0–98 mbsf) consisting mainly of alternating thin- to medium-bedded hemipelagic mud and turbidite sand or mud beds, FA II (98–126 mbsf) dominated by medium- to very thick-bedded turbidite sand or sandy debris flow beds, and FA III (126–178 mbsf) characterized by thick hemipelagic mud without intervening discrete turbidite sand layers. Thermal anomalies from IR scan, mousse-like and soupy structures on split-core surfaces, non-destructive measurements of pressure cores, and comparison of gas-hydrate saturations with sand contents of corresponding pore-water squeeze cakes, collectively suggest that the gas hydrate at the site UBGH1-9 generally occurs in two different types: “pore-filling” type preferentially associated with thin- to medium-turbidite sand beds in the FA I and “fracture-filling” type which occurs as hydrate veins or nodules in hemipelagic mud of the FA III. Gas-hydrate saturation in the FA II is generally anomalously low despite the dominance of turbidite sand or sandy debris flow beds, suggesting insufficient methane supply. 相似文献
10.
Jeongi-Gi Um Pinnaduwa H. S. W. Kulatilake 《Geotechnical and Geological Engineering》2001,19(1):21-42
The granitic rock mass that exists in the shiplock region of the Three Gorges dam site contains a number of major discontinuities and about four sets of minor discontinuities. One hundred and thirty three major discontinuities have been mapped around the shiplock covering an area of 1740×600 m. These major discontinuities were used to perform rock slope kinematic and block theory analyses. Kinematic analyses were performed under the following two cases: (1) assuming all the mapped discontinuities cross the shiplock; (2) using only discontinuities that actually intersect the shiplock. Under case (1) and case (2) the shiplock faces in the proposed permanent shiplock region in fresh rock were found to be stable up to a cut slope of about 45° and 58°, respectively. Block theory was applied to identify different block types that exist on the shiplock faces and to estimate the maximum safe slope angles on the shiplock faces. The orientations of the major discontinuities that actually intersect the shiplocks were considered in this analysis. The total length of the shiplock (1750 m) was divided into 50 m segments. From the stereo-plots, the key blocks (Type I) and/or potential key blocks (Type II) were found for only five segments of the shiplock slopes. It was found that the dip of the cut slope should be less than about 60° to avoid creation of a key block on the proposed shiplock slopes. However, it is important to keep in mind that these conclusions are based on the kinematic analyses performed using only the major discontinuities. Further kinematic as well as kinetic analyses are recommended incorporating minor discontinuities, water forces, earthquake forces etc. before making the final conclusions about the maximum safe slope angle for the shiplock region. 相似文献