Effect of spatial variability of cross‐correlated soil properties on bearing capacity of strip footing

Geotechnical engineering problems are characterized by many sources of uncertainty. Some of these sources are connected to the uncertainties of soil properties involved in the analysis. In this paper, a numerical procedure for a probabilistic analysis that considers the spatial variability of cross‐correlated soil properties is presented and applied to study the bearing capacity of spatially random soil with different autocorrelation distances in the vertical and horizontal directions. The approach integrates a commercial finite difference method and random field theory into the framework of a probabilistic analysis. Two‐dimensional cross‐correlated non‐Gaussian random fields are generated based on a Karhunen–Loève expansion in a manner consistent with a specified marginal distribution function, an autocorrelation function, and cross‐correlation coefficients. A Monte Carlo simulation is then used to determine the statistical response based on the random fields. A series of analyses was performed to study the effects of uncertainty due to the spatial heterogeneity on the bearing capacity of a rough strip footing. The simulations provide insight into the application of uncertainty treatment to geotechnical problems and show the importance of the spatial variability of soil properties with regard to the outcome of a probabilistic assessment. Copyright © 2009 John Wiley & Sons, Ltd.     

Positive effect of porphyrans on the lifespan and vitality of Drosophila melanogaster

The effects of degraded porphyran (P1) and natural porphyran (P) on the lifespan and vitality of Drosophila melanogaster are studied. The porphyrans, added daily to the food medium at 0.2% and 1% concentrations, can significantly increase the lifespan in average of 55.79 and 58.23 d in 0.2% P1 diet females and 1% P1 diet males, extending by 12.29% and 8.60% over the corresponding controls, respectively. The effects of porphyrans on D. melanogaster in heat-stress condition were also examined, and found a remarkable increase in survival time. The results which are consistently associated with the use of porphyrans are related to their free radical scavenger action. Considerable increase in vitality demonstrated that vitalities of middle-aged fly (assessed by measuring their mating capacity) was observed after porphyrans addition. Therefore, porphyrans are effective in reducing the rate of aging, and P1 in low molecular weight is better than natural P.     

Influence of Seawater Temperature on Phytoplankton Growth in Jiaozhou Bay, China

The phytoplankton reproduction capacity (PRC), as a new concept regarding chlorophyll-a and primary production (PP) is described. PRC is different from PP, carbon assimilation number (CAN) or photosynthetic rate ( P^B ) . PRC quantifies phytoplankton growth with a special consideration of the effect of seawater temperature. Observation data in Jiaozhou Bay, Qingdao, China, collected from May 1991 to February 1994 were used to analyze the horizontal distribution and seasonal variation of the PRC in Jiaozhou Bay in order to determine the characteristics, dynamic cycles and trends of phytoplankton growth in Jiaozhou Bay; and to develop a corresponding dynamic model of seawater temperature vs. PRC. Simulation curves showed that seawater temperature has a dual function of limiting and enhancing PRC. PRC‘s periodicity and fluctuation are similar to those of the seawater temperature. Nutrient silicon in Jiaozhou Bay satisfies phytoplankton growth from June 7 to November 3. When nutrients N, P and Si satisfy the phytoplankton growth and solar irradiation is sufficient, the PRC would reflect the influence of seawater temperature on phytoplankton growth. Moreover, the result quantitatively explains the scenario of one-peak or two-peak phytoplankton reproduction in Jiaozhou Bay, and also quantitatively elucidates the internal mechanism of the one- or two-peak phytoplankton reproduction in the global marine areas.     

海上风电楔形单桩基础竖向承载力特性分析

为提高基础利用率增加海上风电设施的可行性，对楔形单桩基础竖向承载力特性进行研究分析。采用PLAXIS 3D 有限元软件建立楔形单桩基础模型，从桩侧摩阻力、桩侧法应力及土体位移对比分析楔形单桩基础与等截面单桩竖向承载特性差异，并探讨内摩擦角、楔角及楔高对承载力的影响。研究表明：楔形单桩基础竖向承载力高于等截面单桩基础，且承载力随着楔角、楔高的增大而增大，提高率最大达24.786%。倾斜侧壁的引入改变了桩侧摩阻力的传递规律；倾斜侧壁挤密桩周土体，桩侧摩阻力与法向应力增大，从而有效提高单桩基础的竖向承载力。研究成果可为今后海上风电单桩基础截面型式的设计提供参考。     

Carbon isotopic fractionation by desorption of shale gases

Geochemical studies of shale gas and conventional reservoirs within the Triassic Yanchang Formation of Xiasiwan and Yongning Field, Ordos Basin show that methane is isotopically depleted in ¹³C as compared to δ¹³C₁ calculated by the Ro based on the relationship between δ¹³C₁ and Ro. Geochemical fractionation during the adsorption/desorption process of shale system may play a significant part in influencing δ¹³C₁ values of shale gas. Two shale core samples from confined coring of the Yanchang Formation were adopted segmented desorption experiments to examine this phenomenon. The results show that the δ¹³C₁ of desorbed gas changes little in the first few phases of the experiments at low desorption levels, but become less negative rapidly when the fraction of desorbed methane exceeds 85%. The desorption process for the last 15% fraction of the methane from the shale samples shows a wide variation in δ¹³C₁ from −49‰ to −33.9‰. Moreover, δ¹³C₁ of all desorbed methane from the shale samples is substantially depleted in ¹³C than that calculated by Ro, according to Stahl and Carey's δ¹³C₁–Ro equation for natural gas generated from sapropelic organic matter. This shows some gases with isotopically enriched in ¹³C cannot be desorbed under the temperature and pressure conditions of the desorption experiments. This observation may be the real reason for the δ¹³C₁ of shale gases and conventional reservoirs becomes more negative in Xiasiwan and Yongning Fields, Ordos Basin. The magnitude of the deviation between the δ¹³C₁ of shale gas and that calculated by Ro may be related to the adsorption capacity of shale or the proportion of absorbed gases. In this way, we may be able to evaluate the relative adsorption capacity of shale in geological conditions by δ¹³C₁ of the shale gas, or by δ¹³C₁ of conventional gas which generated by the shale with certainty. The δ¹³C₁ of conventional gas in Dingbian and Yingwang Fields have no deviation because the TOC value of the hydrocarbon source rock is relatively low.     

Governance fit for climate change in a Caribbean coastal-marine context

Coastal-marine systems in small island developing states of the Caribbean are highly vulnerable to both current and future climate change. Societies navigate these changes in part through processes of governance and the institutions through which governance takes place. The concept of institutional adaptive capacity is used to explore how governance processes and institutional arrangements can be adapted to match the scale and extent of climate change in a case study of the Soufriere Marine Management Area, St. Lucia. Institutional adaptive capacity is analyzed based on the following factors: institutional variety, analytical deliberation and nesting and networks. The analysis is based on 36 semi-structured interviews conducted with key informants from NGOs, cooperatives, management authorities and government agencies. The findings suggest that governance to address climate change in the case study is contingent upon developing holistic, integrated management systems, improving flexibility in existing collaborative decision making processes, augmenting the capacity of local management authorities with support from higher-level government, exploring opportunities for private–social partnerships, and developing adequate social–environmental monitoring programs. These findings have potential implications and lessons for similar settings throughout the Caribbean.     

Experimental research on horizontal bearing behavior of caisson-pile composite foundationEI北大核心CSCD

In this study, four groups of different types of bridge foundation model are tested to research the horizontal bearing behavior of caisson-pile composite foundation in lab based on the Qiongzhou Strait bridge project. The Q-s curve and horizontal ultimate bearing capacity of these four groups of foundations in sandy soil layer are obtained. Pile bending moment and shear force of pile shaft are analyzed in detail. At the same time, the load sharing ratio of caisson and piles is discussed. The results show that the horizontal ultimate bearing capacities of a single caisson foundation are increased by 1.2 times, 1.6 times and 2 times respectively with adding skirts, steel pipe pile, or steel pipe pile and the skirt. The maximum bending moment point is in the middle of the pile shaft, i.e. at about 0.5 m under the mud surface. The horizontal load is borne mainly by the upper caisson foundation and soil layers above the middle upper part of pile. The maximum shear force is found at the joint of pile top of steel pipe and caisson pile, where the reinforcement measures should be taken in practical engineering. The research achievements could provide a better reference for design or construction of caisson-pile composite foundation.     

Ultimate Load Capacity of Offshore Pipeline with Arbitrary Shape Corrosion Defects

A set of generalized solutions are proposed for estimating ultimate load capacity of pipeline with arbitrary corrosion shapes subjected to combined internal pressure, axial force and bending moment. Isotropic and anisotropic material characteristics in longitudinal and circumferential direction of pipeline are also considered in the proposed equations. Simplified numerical method is used to solve the generalized expressions. The comparisons of numerical results based generalized solutions and full-scale experimental results are carried out. The predicted results agree reasonably well with the experiment results. Meanwhile, the effects of corrosion shapes and locations on the ultimate load capacity are studied.     

基于随机森林的中小跨径公路梁桥双柱墩地震易损性模型

为准确建立线路中小跨径梁桥桥墩的地震易损性模型,采用统计工具得到某山区高速公路桥梁双柱墩的结构、几何和材料特性的概率分布,由拉丁超立方体抽样生成桥墩属性数据集,建立了参数化的有限元模型.通过Pushover分析和基于非弹性需求谱的能力谱方法获取双柱墩的地震需求和抗震性能数据点,提出由随机森林(RF)模型建立桥墩地震易损...     

南海西部盐水层CO2埋存潜力评估

南海西部东方1-1、崖城13-1和乐东等气田具有CO2含量高的特点,每年从生产出的天然气中分离出大量的CO2。为了减少CO2在大气中的排放,考虑在莺歌海地区选择合适的盐水层埋存体,拟进行CO2地质埋存示范工程。根据CO2在盐水层中的各种埋存机理,并考虑盐水层构造特征对CO2运移分布的影响,提出了一种较为准确的CO2埋存潜力评估方法,并利用此方法对筛选出的5个备选盐水层进行了评估。评估结果表明,各盐水层埋存潜力巨大,都远远大于示范工程期限内预计的CO2埋存总量,并可将这些盐水层作为将来海南省及临近广东省人为CO2的埋存场所。南海西部东方1-1、崖城13-1和乐东等气田具有CO2含量高的特点,每年从生产出的天然气中分离出大量的CO2。为了减少CO2在大气中的排放,考虑在莺歌海地区选择合适的盐水层埋存体,拟进行CO2地质埋存示范工程。根据CO2在盐水层中的各种埋存机理,并考虑盐水层构造特征对CO2运移分布的影响,提出了一种较为准确的CO2埋存潜力评估方法,并利用此方法对筛选出的5个备选盐水层进行了评估。评估结果表明,各盐水层埋存潜力巨大,都远远大于示范工程期限内预计的CO2埋存总量,并可将这些盐水层作为将来海南省及临近广东省人为CO2的埋存场所。