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.     

Rare earth elements and Opal/CaCO<Subscript>3</Subscript> ratio of sinking particles observed with a time-series sediment trap at the mouth of Tokyo Bay

A time-series sediment trap was deployed from December 1994 to February 2002 at the mouth of Tokyo Bay (35°03′ N, 139°40′ E; water depth, 850 m). Sinking particles were obtained with a time interval of one week at a depth of approximately 100 m above the sea floor. Observed total mass fluxes varied from 3.3 to 226.7 g/m²/day with an average of 28.0 g/m²/day. Concentrations of rare earth elements, Al, Ca and Si in particulate materials were measured. The combustible fraction at 450°C is assumed to be equivalent to the organic matter content. Contents of biogenic materials, namely organic matter, opal and calcium carbonate, were about 30% and the content of lithogenic material was about 70%. Using La/Yb ratios of particles from the sediment trap and Tama-gawa River and surface sediment of Tokyo Bay, it was estimated that about 50% of the lithogenic particles collected in the sediment trap at the mouth of Tokyo Bay originated from resuspended surface sediment in Tokyo Bay. An increasing trend of Opal/CaCO₃ ratio in the sinking particles was found in the spring season. It is suggested that the relative increase of diatoms is due to the decreasing dissolved inorganic nitrogen input into Tokyo Bay.     

Gravitational Sedimentation Behavior of Sensitive Marine Ariake Clays

It has been well documented that natural marine Ariake clays are sensitive clays. In this study, extensive data of marine Ariake clays are obtained to investigate the gravitational compression behavior for sensitive clays. Analysis results indicate that the compression behavior of remolded Ariake clays is not different from that of other remolded/reconstituted soils. But natural Ariake clays do not follow the gravitational compression pattern reported by Skempton (1970) for natural sedimentary soils. At a given value of effective overburden pressure, the void ratios of natural Ariake clays are almost independent of liquid limits. Most natural Ariake clays lie above the sedimentation compression line proposed by Burland (1990). When the liquid limit is larger than 90% and the ratio of natural water content over liquid limit ranges 0.8-1.1, the natural Ariake clays lie around the sedimentation compression line. In addition, the natural Ariake clay with higher value of the ratio of natural water content over liquid limit lies above the natural Ariake clay with lower value of the ratio of natural water content over liquid limit. Salt removal is the most probable cause for such a phenomenon.     

利用高密度电阻率法进行断层破碎带探查的数值模拟方法

为明确不同条件下断层破碎带的异常特征 ,提高高密度电阻率法 (HDR)的应用效果 ,该文在大量探测实例的基础上提出断层破碎带的地电模型 ;用有限元数值模拟的方式计算出不同地表电性层的情况下 ,高、低阻断层破碎带在不同电测的异常特征并确定最佳采集装置形式 ;并正演模拟倾斜断层的异常分布形态 ,给出为提高视电阻率断面对断层产状反映能力的数据处理方法     

Simulation of upper-ocean biogeochemistry with a flexible-composition phytoplankton model: C, N and Si cycling in the western Sargasso Sea

We report the first application of a biogeochemical model in which the major elemental composition of the phytoplankton is flexible, and responds to changing light and nutrient conditions. The model includes two phytoplankton groups: diatoms and non-siliceous picoplankton. Both fix C in accordance with photosynthesis-irradiance relationships used in other models and take up NO₃⁻ and NH₄⁺ (and Si(OH)₄ for diatoms) following Michaelis-Menten kinetics. The model allows for light dependence of photosynthesis and NO₃⁻ uptake, and for the observed near-total light independence of NH₄⁺ uptake and Si(OH)₄ uptake. It tracks the resulting C/N ratios of both phytoplankton groups and Si/N ratio of diatoms, and permits uptake of C, N and Si to proceed independently of one another when those ratios are close to those of nutrient-replete phytoplankton. When the C/N or Si/N ratio of either phytoplankton group indicates that its growth is limited by N, Si or light, uptake of non-limiting elements is controlled by the content of the limiting element in accordance with the cell-quota formulation of Droop (J. Mar. Biol. Ass. U.K 54 (1974) 825).We applied this model to the Bermuda Atlantic Time-series Study (BATS) site in the western Sargasso Sea. The model was tuned to produce vertical profiles and time courses of [NO₃⁻], [NH₄⁺] and [Si(OH)₄] that are consistent with the data, by adjusting the kinetic parameters for N and Si uptake and the rate of nitrification. The model then reproduces the observed time courses of chlorophyll-a, particulate organic carbon and nitrogen, biogenic silica, primary productivity, biogenic silica production and POC export with no further tuning. Simulated C/N and Si/N ratios of the phytoplankton indicate that N is the main growth-limiting nutrient throughout the thermally stratified period and that [Si(OH)₄], although always limiting to the rate of Si uptake by diatoms, seldom limits their growth rate. The model requires significant nitrification in the upper 200 m to yield realistic time courses and vertical profiles of [NH₄⁺] and [NO₃⁻], suggesting that NO₃⁻ is not supplied to the upper water column entirely by physical processes. A nitrification-corrected f-ratio (f_NC), calculated for the upper 200 m as: (NO₃⁻ uptake—nitrification)/(NO₃⁻ uptake+NH₄⁺ uptake) has annual values ranging from only 0.05–0.09, implying that 90–95% of the N taken up annually by phytoplankton is supplied by biological regeneration (including nitrification) in the upper 200 m. Reported discrepancies between estimates of organic C export based on seasonal chemical changes and POC export measured at the BATS site can be almost completely resolved if there is significant regeneration of NO₃⁻ via organic-matter decomposition in the upper 200 m.     

闽江口的盐、淡水混合

采用盐、淡水混合比的概念研究闽江口的混合状态，并确定了分层、部分混合、高度混合３种类型的分类指标。研究表明，闽江口主要水道的盐、淡水混合以部分混合为主，其次是分层，高度混合出现的机率较少；盐水异重流发育良好，混合状态的变化与潮流速的变化不相一致；盐水入侵时混合比相对较小，后退时相对较大。闽江口是一个径、潮量比值较小的强潮河口，按照一般规律，其盐、淡水混合应该出现高度混合型，但在闽江口的主汊道中发生     

厦门湾水体中颗粒有机碳的垂向输出通量:234Th/238U不平衡的应用

对厦门湾塔角附近海域某站位叶绿素 a、POC、初级生产力、234Th/238U不平衡进行的周日变化研究表明,POC含量介于14.4～34.6 mmol/m3之间,其中碎屑有机碳与活体有机碳所占份额分别为74%～92%和8%～26%.POC垂直分布呈现由表及底降低的趋势,且白昼期间POC含量高于晚间,说明研究海域POC含量与生物过程具有密切联系.初级生产力水平在1d之中变化达5倍,垂直分布亦随深度增加而降低,与叶绿素a的变化相对应.短时间(2h)培养获得的初级生产力水平明显高于长时间培养(24 h)的结果,证实部分新固定的碳被优先呼吸排出.结合234Th/238U不平衡法获得的颗粒态234Th输出通量及输出界面颗粒物中的POC/P_Th比值,可计算出真光层 POC的垂向输出通量为16.0mmol/(m2·d),其中碎屑有机碳与活体有机碳贡献的数量分别为13.3和2.7mmol/(m2·d).POC输出通量与初级生产力的比值(ThE比值)平均为0.31,真光层POC停留时间平均为11d.上述结果与Aksnes和Wassmann[1]的模型计算结果相吻合,但与其他大多数模型的结果仍存在一定的差异.     

Particulate n-alkanes and fatty acids in the Changjiang river system

Particulate samples were collected from the Changjiang river system during a flood period, in May 1997, and POC, stable isotope and lipids associated with particles were examined. Results showed the decrease (0.84% ～ 1.88%) of organic carbon content from the upper reaches to the estuary.δ13C values of particulate organic carbon was in the range of -24.9×10-3 to -26.6×10-3, which were close to the isotopic signature of continental C3 vegetation. Total particulate n-alkanes concentrations varied from 1.4 to 10.1μg/dm3,or from 23.7 to 107μg/g of total suspended matter. Fatty acids were present in all the samples, from 1.4 to 5.4μg/dm3, with saturated and unsaturated straight-chain and branched compounds in the carbon number range from C12 to C30. Both δ13C and the ratio of carbon content to nitrogen content indicate the predominance of terrestrial inputs (soil organic matter) among the particles. The biomarker approach has been used to identify the relative portion of terrigenous and autochthonous fraction in the particulate samples. The distribution of fatty acids suggests a striking phytoplanktonic and microbial signal in most particle samples. The terrestrial alkanes are used to estimate the contribution of terrestrial inputs along the mainstream.