Assessment of sediment contamination in Casco Bay, Maine, USA

The current status of contaminant concentrations in Casco Bay, decadal trends of these contaminants and changes in their geographical distribution are assessed using sediment samples collected approximately 10 years apart. In general, regulated contaminants appeared to be decreasing in concentration. Total PAH and dioxins/furans concentrations did not significantly change over this period. Total organochlorine pesticides, 4,4-DDE, 4,4-DDD, total DDT, PCB, tributyltin and total butyltin decreased in concentration. Trace element concentrations in sediments decreased at the majority of the sampling sites for chromium, nickel, and selenium while arsenic, cadmium, copper, lead, mercury, silver, and zinc remained relatively constant. None of the contaminants measured has increased by more than a factor of 2. Selected sites located in the Inner Bay, where concentrations are higher and new inputs were more likely, showed increased concentrations of contaminants. Most contaminants were not found at concentrations expected to adversely affect sediment biota based on ERL/ERM guidelines.     

吸力式桶形基础多桶组合结构承载力特性研究

海洋采油平台结构中一般采用多桶组合基础型式,然而迄今对多桶组合结构尚缺乏理论分析和实验研究。本文针对我国第一座吸力式桶形基础采油平台CB20B,基于单桶基础在复合加载模式下的承载力特性,建立了双桶、四桶组合基础的三维有限元数值计算模型,探讨了对称多桶基础结构与单桶基础结构的承载力特性之间的相互关系,阐述了不同桶间距的多桶组合结构地基破坏机制,为工程设计提供参考依据。     

基坑开挖对临近地基极限承载的影响性状数值分析

采用弹塑性有限元分析方法,分析了悬臂式排桩支护的基坑开挖对邻近地基条形基础下极限承载力的影响性状。主要考虑了在基坑开挖深度、荷载与基坑的距离、荷载宽度、支护刚度等因素的影响下地基极限承载力的减损性状。研究表明,基坑开挖深度H较浅时,对地基极限承载力P_u的影响较小,P_u随H的增大略有降低,随着开挖深度的增加,H对P_u值的影响显著增大,且P_u值显著降低;当L/H≤2时,荷载与基坑的距离L对地基极限承载力P_u的影响很大,地基极限承载力P_u随L的减小而显著减小,当L/H>3时,L的影响逐渐减小,且P_u逐渐趋近于无基坑开挖时的值;P_u随地基荷载作用宽度B的增大而呈线性增大;支护桩的位移越小,P_u值越接近无基坑开挖时的地基极限承载力。     

常压立式储油罐地震应力的有限元计算

采用有限元方法 ,考虑在静载和动载共同作用下 ,对常压立式拱顶储油罐的地震应力进行了计算分析 ,给出了轴向应力的分布状态 ;并与相关抗震设计规范中的验算公式得出的结果进行了比较。结果表明 :由于地震的动力作用 ,储油罐的受力状态不是均匀分布 ,出现了峰值和谷值 ,而这些应力峰值大于工业设备抗震鉴定标准和石油化工设备抗震鉴定标准中公式的计算应力值 ,这应引起足够的注意。     

长江河口硅和磷生源要素质量浓度的变化特征

根据近年来长江河口区域内大通水文站的记录和近期在长江入海河口区上海段多个采样点的生源要素质量浓度实测数据,比较水中可溶性硅酸盐和磷酸盐的质量浓度,分析在长江入海河口区水中硅和磷元素含量的主要变化特征.结果表明,长江水中的硅酸盐和磷酸盐从长江入海河口进入大海的过程中,其质量浓度有降低的趋势,它们在长江入海河口的多年的质量浓度变化趋势是相反的.长江入海河口区域上游的磷酸盐质量浓度升高幅度较大,而硅酸盐变化不大,硅酸盐、磷酸盐质量浓度在长江河口区进入海洋的过程中迅速降低.      

某水电站进水口边坡变形特征及稳定性评价

某水电站是澜沧江中、下游梯级开发的关键工程,其进水口高边坡地质条件复杂。通过对该电站进水口边坡的物质组成、结构特征、以及边坡开挖等因素的综合分析研究,阐述了其变形机理,说明此高边坡存在如下变形破坏形式:①楔形体滑动破坏;②扩展式的平面型塌滑和滑移型崩塌破坏;③卸荷松弛变形破坏。采用三维块体分析和有限元数值模拟,分析了这类边坡在开挖过程中的应力变形特征及其变化规律。     

基于谐波沉降的管道力学分析*

为避免地面沉降引发的油气管道事故,研究沉降管道的力学特性,提出基于谐波沉降的管道力学评估方法。以中国石化某沉降管道为研究对象,通过现场测量的方法获得沉降区管道高程,利用傅里叶级数展开对不均匀沉降数据进行处理分析,获得管道谐波沉降的拟合函数。建立ANSYS有限元模型,采用土弹簧模型模拟非沉降区管道与土体相互作用关系,将谐波沉降作为位移载荷施加到沉降区管道,对含内压管道的沉降进行数值模拟,分析其应力、应变分布规律。结果表明:沉降与非沉降交界处管道应变及应力最大,基于应变的评估准则,管道运行状态为安全,为应急响应提供支撑。     

A hybrid method for quasi-three-dimensional slope stability analysis in a municipal solid waste landfill

Limited space for accommodating the ever increasing mounds of municipal solid waste (MSW) demands the capacity of MSW landfill be maximized by building landfills to greater heights with steeper slopes. This situation has raised concerns regarding the stability of high MSW landfills. A hybrid method for quasi-three-dimensional slope stability analysis based on the finite element stress analysis was applied in a case study at a MSW landfill in north-east Spain. Potential slides can be assumed to be located within the waste mass due to the lack of weak foundation soils and geosynthetic membranes at the landfill base. The only triggering factor of deep-seated slope failure is the higher leachate level and the relatively high and steep slope in the front. The valley-shaped geometry and layered construction procedure at the site make three-dimensional slope stability analyses necessary for this landfill. In the finite element stress analysis, variations of leachate level during construction and continuous settlement of the landfill were taken into account. The "equivalent" three-dimensional factor of safety (FoS) was computed from the individual result of the two-dimensional analysis for a series of evenly spaced cross sections within the potential sliding body. Results indicate that the hybrid method for quasi-three-dimensional slope stability analysis adopted in this paper is capable of locating roughly the spatial position of the potential sliding mass. This easy to manipulate method can serve as an engineering tool in the preliminary estimate of the FoS as well as the approximate position and extent of the potential sliding mass. The result that FoS obtained from three-dimensional analysis increases as much as 50% compared to that from two-dimensional analysis implies the significance of the three-dimensional effect for this study-case. Influences of shear parameters, time elapse after landfill closure, leachate level as well as unit weight of waste on FoS were also investigated in this paper. These sensitivity analyses serve as the guidelines of construction practices and operating procedures for the MSW landfill under study.     

Cd-tolerant Suillus luteus: A fungal insurance for pines exposed to Cd

Soil metal pollution can trigger evolutionary adaptation in soil-borne organisms. An in vitro screening test showed cadmium adaptation in populations of Suillus luteus (L.: Fr.) Roussel, an ectomycorrhizal fungus of pine trees. Cadmium stress was subsequently investigated in Scots pine (Pinus sylvestris L.) seedlings inoculated with a Cd-tolerant S. luteus, isolated from a heavy metal contaminated site, and compared to plants inoculated with a Cd-sensitive isolate from a non-polluted area. A dose-response experiment with mycorrhizal pines showed better plant protection by a Cd-adapted fungus: more fungal biomass and a higher nutrient uptake at high Cd exposure. In addition, less Cd was transferred to aboveground plant parts. Because of the key role of the ectomycorrhizal symbiosis for tree fitness, the evolution of Cd tolerance in an ectomycorrhizal partner such as S. luteus can be of major importance for the establishment of pine forests on Cd-contaminated soils.     

单块集尘板振打加速度的有限元分析

采用有限元分析软件ABAQUS,对单块集尘板振打加速度进行了分析计算。并将计算结果与解析法和实测法结果进行对比。对比结果表明,有限元计算值更接近于实测值。用有限元法对某厂实际运行的电除尘器加速度进行求解,计算结果与实际基本吻合。由于有限元法能非常方便地处理各种复杂板型、不同的悬挂方式、振打锤的大小以及振打方式,因此,有限元法对于现有极板的分析与新型极板的研究均具有重要的实际意义。