Strength Characteristics of the Cement-Stabilized Surface Layer in Dredged and Reclaimed Marine Clay, Korea

A series of tests in both laboratory and field were performed to investigate the engineering and mechanical properties, especially flexural strength, of cement-stabilized soils. The strength of cement-stabilized soils mainly depends on water-to-cement ratio and curing temperature. The higher curing temperature and the longer curing time, the higher strength in cement-stabilized soils generates. The high ratio of water-to-cement results in lower strength. The compressive strength observed in the field is similar to the strength in the laboratory. Field tests on a cement-stabilized soil layer indicate that the strength is significantly affected by the thickness of the improved layer, which is directly related to the moment of inertia. In addition, the failure shape observed in a cement-stabilized layer in the field looks likes a bending failure type, because the flexural tensile strength, rather than the compressive strength, mainly dominates the failure of cement-stabilized layer. The flexural tensile strength is closely related to the moment of inertia. Therefore, the flexural tensile strength should be considered for determining the thickness and strength in improvement of soft clay.     

An approach to analyses of periphytic ciliate colonization for monitoring water quality using a modified artificial substrate in Korean coastal waters

Structural and functional parameters of periphytic ciliate communities were studied for monitoring water quality in Korean coastal waters during April 2007. The PFES (polyurethane foam enveloped slide) system, a modified glass slide method, was used to analyze periphytic ciliate colonization in marine ecosystems. A total of 27 ciliate species were identified using living observation and silver impregnation method with this system. Although the ciliate colonizations had similar species composition, they represented considerable differences in both structural and functional parameters between the PFES system and the conventional slide system. The species diversity, evenness and the colonization rate (G) were distinctly higher, but the time for reaching 90% equilibrium species number (T_90%) was shorter in the PFES system than those on the naked slides. Results suggest that the PFES system is more effective than the conventional slide method for periphytic ciliate colonization with high species diversity, evenness, and colonization rate in marine ecosystems.     

Strength Characteristics of the Cement-Stabilized Surface Layer in Dredged and Reclaimed Marine Clay,Korea

ABSTRACT

A series of tests in both laboratory and field were performed to investigate the engineering and mechanical properties, especially flexural strength, of cement-stabilized soils. The strength of cement-stabilized soils mainly depends on water-to-cement ratio and curing temperature. The higher curing temperature and the longer curing time, the higher strength in cement-stabilized soils generates. The high ratio of water-to-cement results in lower strength. The compressive strength observed in the field is similar to the strength in the laboratory. Field tests on a cement-stabilized soil layer indicate that the strength is significantly affected by the thickness of the improved layer, which is directly related to the moment of inertia. In addition, the failure shape observed in a cement-stabilized layer in the field looks likes a bending failure type, because the flexural tensile strength, rather than the compressive strength, mainly dominates the failure of cement-stabilized layer. The flexural tensile strength is closely related to the moment of inertia. Therefore, the flexural tensile strength should be considered for determining the thickness and strength in improvement of soft clay.     

Geochemical characterization of the organic matter, pore water constituents and shallow methane gas in the eastern part of the Ulleung Basin, East Sea (Japan Sea)

Abstract Geochemical analyses of sediments, pore water and headspace gas of the piston cores taken from the eastern part of Ulleung Basin of the East Sea (Japan Sea) were carried out to assess the origin of the sedimentary organic matter and interstitial fluid. Several tephra layers within the core are identified as the Ulleung‐Oki (10.1 ka), the Aira‐Tanzawa (23 ka) and the Ulleung‐Yamato (30.9 ka) tephras. With the exception of these volcanic layers, the cores consist predominantly of muddy sediments that contain >0.5% total organic carbon. Atomic C/N ratios and δ¹³C_org values suggest that the organic matter originated from marine algae rather than from land vascular plants, whereas Rock‐Eval pyrolysis suggests that the organic matter is thermally immature and comes from a land vascular plant (Type III). These conflicting results seem to be caused by the heavy oxidization of the marine organic matter. Sulphate concentration profiles of pore waters show strongly linear depletion (r² > 0.97) with sediment depth. The estimated sulphate–methane interface (SMI) depth using the sulphate concentration gradient was nearly 3.5 m below seafloor (mbsf) in the southern part of the study area, and deeper than 6 mbsf in the northern part of the area. The difference in SMI depths is likely associated with the amount of the methane flux. The methane concentration below the SMI in the two southern cores increases rapidly, implying the occurrence of methanogenesis and anaerobic methane oxidation (AMO). In contrast, the two northern cores have a low methane concentration below the SMI. values measured from all cores were in the range of −83.5 to −69.5‰, which suggests that the methane derives from a methanogenic microbe. values become decreased toward SMI, but increased below SMI; therefore, has eventually the minimum value near the SMI. The values are also decreased when the methane concentration is increased. These phenomena support the typical occurrence of AMO in the study area.     

Climate variability and its effects on major fisheries in Korea

Understanding in climate effects on marine ecosystem is essential to utilize, predict, and conserve marine living resources in the 21s t century. In this review paper, we summariz ed t h e past history and current status of Korean fisheries as well as the changes in climate and oceanographic phenomena since the 1960s. Ocean ecosystems in Korean waters can be divided into three, based on the marine commercial fish catches; the demersal ecosystem in the Yellow Sea and the East China Sea, the pelagic ecosystem in the Tsushima Warm Current from the East China Sea to the East/Japan Sea, and the demersal ecosystem in the northern part of the East/Japan Sea. Through the interdisciplinary retrospective analysis using available fisheries, oceanographic, and meteorological information in three important fish communities, the trend patterns in major commercial catches and the relationship between climate/ environmental variability and responses of fish populations were identified. Much evidence revealed that marine ecosystems, including the fish community in Korean waters, has been seriously affected by oceanographic changes, and each species has responded differently. In general, species diversity is lessening, and mean trophic level of each ecosystem has decreased during the last 3~4 decades. Future changes in fisheries due to global warming are also considered for major fisheries and aquaculture in Korean waters.     

Biostratigraphy and Paleoenvironment in Cheju Sedimentary Basin, Determined by Materials from Exploration Wells Geobuk-1 and Okdom-1

A micropaleontological analysis was made using materi-als from exploration wells Geobuk-1 (Td:2 72 2 .5m) andOkdom-1 (Td:2 90 3 .7m) for the purpose of biostratigraphicand paleoenvironmental interpretation of the Cheju sedimenta-ry basin.Two wells yield relatively abundant microfossilssuch as dinoflagellates,calcareous nannofossils,pollen andspores.The biostratigraphic and paleoenvironmental settingsanalyzed by microfossil assemblages seem to be closely relatedto the framework of the local t…     

黄海及周边地区α中尺度对流系统发生的环境条件

使用日本GMS - 5静止卫星红外云图普查了 1993年 7、8月份黄海及周边地区α中尺度对流系统 (MαCS)的发生情况 ,并用合成和客观分析诊断的方法考察MαCS两个活跃期和两个静寂期的大尺度环境场的热力和动力条件。结果表明 ,MαCS活跃期和静寂期的合成诊断场有显著的不同 ,从而揭示了黄海地区发生MαCS的环境条件主要为 :①低层为高相当位温的暖湿空气 ;②中低层的条件性不稳定的大气层结及暖平流 ;③强而稳定的西南低空急流 ;④低层的辐合及中层不太强的上升运动 ;⑤副热带西风急流出口区右侧的高层辐散。