Failure Resistance of Historic Stone Bridge Structure of Charles Bridge. II: Susceptibility to Floods

The paper is a follow-up to the first part devoted to an analogical problem investigated with a view to the degradation of the stone structure due to the effects of nonstress load, and it deals with the probability problem of the bridge structure collapse under the effect of an extreme flood wave. The paper presents the results of the numerical analysis of the response of the historic stone bridge structure of Charles Bridge of the 14th century to the flood wave effect simulated by angular rotation, subsidence, and shifting in the footing bottom of a bridge pier. Special focus is on the effect of interventions into the stone bridge structure dating back to the last major overhaul of 1967–1975, particularly, on the effect of the reinforced concrete slab (tie plate) connecting the opposite bridge breast walls increasing the rigidity of the breast walls and their structurally efficient connection to the vaults of the bridge arches. The numerical analyses performed point out the prevailing negative effects of the implemented interventions in terms of structural rigidity of the stone bridge structure exposed to the effect of a flood wave.     

Flood Damage to Historic Buildings and Structures

This paper presents typical examples of damage to immovable cultural heritage due to flooding. Flooding can damage architectural heritage, historic infrastructure consisting of individual structures, buildings, and objects, as well as objects of art standing alone or firmly attached as an integral part of buildings. All these objects are subjected to various forces and actions during flood situations. These forces can be categorized according to the types of damage that they can cause: horizontal static pressure of raised water; upward hydrostatic pressure; dynamic low velocity streams; dynamic high-velocity streams; dynamic impact of waves; dynamic impact of floating objects; compacting of soils or infill; changes in subsoil conditions; saturation of materials with water; contamination of materials with chemical and biological agents; formation of barriers; ice floes; and postflood effects. These typical actions may occur in combinations and work in synergy. Typical illustrative examples of damage caused by individual actions are presented in the paper, which goes on to present some general lessons applicable for the most vulnerable categories of immovable heritage objects.     

Historic Building Stones and Flooding: Changes of Physical Properties due to Water Saturation

Natural stone is a common material in historic constructions. Flood events may directly affect surfaces of historic stone buildings. Since ashlars and stone sculptures often carry valuable cultural information, a more detailed knowledge about changes in physical properties due to water saturation is crucial for the assessment of their surface stability in case of flooding. Water saturation of stones leads to loss of mechanical strength and to expansion of volume (hydric dilatation). On the basis of data from literature, a rough scheme of vulnerability is suggested for different kinds of building stones. The majority of igneous and metamorphic rock types with dense crystalline structure are not vulnerable to flooding, whereas some types of pyroclastic rocks (tuffs) as well as clay-bearing sandstones are highly vulnerable. Detailed laboratory investigations on Elbe sandstone demonstrate the influence of petrographic features on material behavior due to water saturation. Results of laboratory tests are in good accordance to on-site observations made after the great summer flood in Dresden, Germany in 2002.     

Failure Resistance of the Historic Stone Bridge Structure of Charles Bridge. I: Susceptibility to Nonstress Effects

The monitoring of deformations of the stone structure of Charles Bridge in Prague proved the gravity and relevance of nonstress effects (temperature, moisture content) on cyclic deformations and permanent strain accompanied by a gradual disintegration of its stone masonry, growing tilt of the breast walls, and development of cracks in the masonry of the stone bridge structure. Each deformation cycle is accompanied by a gradual growth in permanent deformations. The “unmanifested” primary deformation due to, e.g., a temperature change causes a mechanical state of tension, and it is mainly the tensile stresses thus arising that contribute to the development of tensile cracks in the stone masonry.     

Geotechnical Problems of Cultural Heritage due to Floods

Flood events demonstrate devastating effects not only on materials and structures in contact with flowing surface water. Equally important is the behavior of foundations in interaction with subsoil. This contribution gives an overview of different phenomena which arise in subsoil and at the foundation level during the groundwater rise accompanied by several case histories related to cultural heritage. Possible geotechnical measures are discussed as well.     

物探在文物遗址治理中的应用

叙述了物探在文物遗址病害治理中的应用,介绍了微重力测量、地质雷达、浅震映像法、瑞雷波法的基本原理及其对岩溶洞穴、溶槽溶沟、溶蚀裂隙的位置和埋深的探测。钻孔结果对物探效果的验证,表明物探在文物遗址病害治理中可以发挥重要作用。     

Effects of Flood Flow on Flood Plain Soil and Riparian Vegetation in a Gravel River

Field observations were performed to determine the effects of flood flow on the geometrical and chemical characteristics of flood plain soil and the distribution of riparian vegetation in a gravel river. The results of the observations show a decrease in the amounts of the particulate nutrients in the flood plain soil during fairly large flood, because the fine sands that serve as a nutrient source were removed by the flood flow. Numerical simulations for the transport of suspended sediments were performed by varying the peak discharge of the flood, and the change of the particulate nutrients in flood plain soil was estimated by using the results of the simulations. The numerical analysis predicts the reduction of the particulate nutrients in the flood plain soils well. The particulate nutrients on the flood plains decrease if the discharge exceeds the flood of approximately 2 year return period in the observation area.     

Integrated Subsurface Modeling and Risk Assessment of Petroleum-Contaminated Sites in Western Canada

Soil and groundwater contamination can pose a variety of impacts and risks to communities. Identification of management schemes with sound environmental and socio-economic efficiencies is desired. Before any decisions regarding site remediation actions can be made, three major questions may have to be answered. They are namely “What happened underground?”, “What will happen in the future under the given remediation scenarios?”, and “Are there specific risks to the surrounding community?”. In this study, an integrated modeling and risk assessment method is developed for effectively managing petroleum-contaminated sites through technically answering the above questions. It presents an integral concept that integrates issues of multicontaminant transport simulation, biodegradation modeling, health risk assessment, and site remediation for real-world problems within a general decision support framework. The developed method is applied to a petroleum-contaminated groundwater system in western Canada for identifying cost-effective management schemes with improved environmental and socio-economic efficiencies. The research outputs are directly useful for the decision maker to gain insight into the site and to make remediation decisions.     

Probability of Pressure Deficit in On-Demand Branched Networks and Incorporation into Design Decisions

This technical paper presents analytical expressions to estimate the probability function of head losses in any path of an on-demand branched irrigation network. They are developed for estimating the probability of pressure deficit of a given magnitude at any hydrant. They are also useful for examining the probability of a power deficit at a pumping station designed to guarantee service to a hydrant, as well as the head characteristic curve of the distribution system linked to a definite probability. All this quantified information is useful for decision making on network design and performance. The probabilities calculated with the developed expressions can be taken as complementary or alternative concepts to Clément’s classical design flow method, which is taken here as a benchmark for comparisons. Illustrative examples of network designs are presented to validate the proposed expressions. The least cost design solutions using Clément’s design flows are compared with design solutions here obtained to get the same probability of pressure deficit at the most unfavorable hydrants. The new solutions are less expensive because the flow constraint can be avoided.     

Fuzzy Reliability Analyzer: Quantitative Assessment of Risk Events in the Construction Industry Using Fuzzy Fault-Tree Analysis

Fault trees are deductive techniques constructed by taking a system failure event and deconstructing it into its root causes (basic events, gate events). Fault trees can be solved qualitatively, by determining minimal cut sets, and quantitatively, by calculating the probability of occurrence of the risk event. In conventional fault-tree analysis (FTA), the probability of occurrence for all basic events must be assessed in order to allow for quantitative fault-tree analysis. However, conducting quantitative fault-tree analysis, especially in construction projects, entails several difficulties owing to the lack of sufficient data, leading to an approximation of the probability of occurrence for some basic events. Assuming probabilities for any basic event will add further uncertainty to the analysis, resulting in a potentially questionable end result. To overcome the challenge of assessing probabilities, this paper presents a comprehensive framework in which experts can use linguistic terms rather than numerals to assess the probability of occurrence of basic events. Fuzzy arithmetic operations are used to perform quantitative fault-tree analysis. Fuzzy Reliability Analyzer (FRA) was developed to automate both qualitative and quantitative FTA. The method presented is demonstrated via a case study to quantify the probability of failure of horizontal directional drilling (HDD) in meeting project objectives. Fourteen minimal cut sets were identified and the fuzzy probability (FPro) of the top event (TE) was calculated. The proposed approach offers the advantage of allowing experts to express themselves linguistically to assess the probability of occurrence of basic events, which is more appropriate for the construction domain. In addition, the proposed method offers the risk analyst the advantage of ranking basic events according to their level of contribution to the probability of the risk event, which can help in establishing more effective risk response strategies.     

拉萨河流域河水重金属分布特征及污染风险评价

在分析拉萨河流域中下游和支流堆龙曲16个采样点水样的水质理化性质的基础上,对拉萨河流域主要重金属的含量和分布进行了分析,并运用综合污染指数法对其进行了污染风险的初步评价。结果表明,拉萨河流域As、Cd、Fe、Cu、Zn和Mn 6种重金属含量未超过《地表水环境质量标准》(GB 3838—2002)中Ⅰ类水的标准。这6种重金属含量与pH间均不存在显著相关性,其中Cd、Cu、Mn的污染具有一定的同源性,而As、Mn、Fe、Cu的污染是多源的。拉萨河流域中游、下游、支流堆龙曲和整个流域的重金属污染综合指数分别为0.048、0.192、0.072和0.117,污染程度的分级均是无污染。由于人类活动更加密集,拉萨河流域下游的重金属污染指数明显高于中游和支流堆龙曲。     

某铀尾矿库周边地下水重金属污染特征及健康风险研究

选取某铀尾矿周边地下水为对象,通过野外取样与室内试验,分析铀尾矿周边地下水重金属的存在形态及分布特征,采用美国环保局(USEPA)推荐的风险评价模型对地下水重金属污染进行健康风险评价。结果表明,研究区地下水重金属主要以毒性较强的形态存在。重金属Cr和Cd的分布总体上是西北部较高、东南部较低;Cu的分布是东部较高、西部较低;Pb的分布是尾矿库附近和北部相对较高。健康风险评价表明,成人和儿童总非致癌风险分别为1.95E-09a-1和3.06E-09a-1,总致癌风险分别为3.17E-07a-1和4.96E-07a-1,均在EPA和ICRP推荐的可接受范围内。     

萍水河地表水重金属污染特征及健康风险评价

以萍水河何雁桥至向阳湖段为研究对象,在21个采样点采集地表水样品,首先分析水体中10种重金属的空间污染特征,然后运用多元统计法对重金属间的相关性进行分析,最后采用USEPA推荐的健康风险评价模型评价重金属经饮水途径对成人和儿童产生的健康风险。结果表明,V、Fe、Mn的最大值均超过《地表水环境质量标准》(GB 3838—2002)Ⅲ类水质标准,最大超标2.3倍,重金属浓度均值大小依次为：Fe>Mn>V>Zn>Mo>As>Cu>Cd>Pb>Cr;从空间分布特征看,重金属多集中在研究区上游和下游,受人类工农业活动影响明显。Cu与Fe、Cu与Cr、Fe与Mn、As与V间呈现显著相关,相关系数分别为0.704、0.677、0.671和0.440,具有相同的来源或转换过程;Mo与Cu、Mo与Cr呈负显著相关,相关系数分别为-0.51、-0.44,表明来源不同或者两者间相互抑制。成人与儿童的健康总风险均大于最大可接受风险水平1.0×10-6,污染物致癌风险值比非致癌风险高3~4个数量级,总健康风险主要由Cr、As、Cd产生,儿童健康风险比成人健康风险高。模型参数的合理取值和本土化是精确量化地表水中重金属对人体健康影响的关键要素,特别对儿童进行健康风险评价应分年龄段计算。     

后污染期龙江河底泥中镉铅的形态分布及风险评价

为了解龙江河镉污染事件后污染期沉积物中镉、铅的形态分布和风险状况,对龙江河拉浪、怀远、宜州、湖长4个河段的底泥进行采样分析,用Tessier逐级浸提法测试镉、铅的形态及含量,用地累积指数法和潜在生态风险指数法评价污染程度和风险等级。结果显示,龙江河底泥中镉、铅主要以氢氧化物、碳酸盐、硫化物的形态存在,氢氧化物、碳酸盐沿河均匀分布,硫化物及总镉、总铅的含量沿河逐渐降低。拉浪、怀远河段镉的地累积指数等级为3级,属中度污染,与2012年3月和7月的6级极重污染相比污染程度已大幅下降;宜州、湖长河段镉的污染等级为2级,属偏中污染。拉浪河段底泥中镉的潜在生态风险等级为较重风险,怀远、宜州、湖长河段镉的潜在生态风险为中风险等级。对于底泥中的铅,4个河段均处于无污染状态和低风险等级。     

北京地区农用地土壤重金属污染与健康风险评价

为系统了解北京地区农用地土壤重金属污染状况,通过检索收集2000年以来北京地区农用地土壤重金属污染相关研究文献数据,并结合空间分析、地累积指数法和人体健康风险评价等方法对其分布规律、污染状况和健康风险进行研究。结果表明,北京地区农用地土壤中8种重金属（As、Cd、Cr、Cu、Hg、Ni、Pb和Zn）平均含量均低于筛选值,但大部点位的重金属含量已超背景值且存在明显的空间变异。地累积指数污染评价显示区域土壤Hg和Cr地累积风险最大,其污染点位占比分别达82%和67%,其余重金属累积污染风险较低。不同暴露途径下,各单一重金属或复合作用导致的非致癌和致癌风险均为可接受水平。但相较于其他重金属而言,土壤As的潜在致癌和非致癌风险最大,建议相关部门加强区域土壤As的监测与管控治理,以期实现区域农业活动可持续绿色安全生产。     

某稀土冶炼厂及周边环境土壤中放射性核素分布特征与风险评价

为查明某稀土冶炼厂及周边环境土壤中放射性核素污染程度及危害,分析某稀土冶炼厂及其周边土壤中~(238)U、~(232)Th、~(226)Ra和~(40)K的分布特征,采用地质累积指数法、内梅罗污染指数法,健康风险评价等方法对研究区土壤放射性核素进行了研究。结果表明,4种放射性核素浓度范围分别为~(238)U 50.73～6 275.00、~(232)Th 131.00～3 581.00、~(226)Ra 45.63～5 952.00、~(40)K 59.90～1 065.00Bq/kg。由于自然淋滤和渗漏作用,随深度增加,~(238)U、~(232)Th、~(226)Ra和~(40)K浓度呈减小趋势。地质累积指数法表明,4、5号采样点~(238)U、~(232)Th和~(226)Ra为主要污染核素,其评价指数分别为(3.14、2.81、1.16)、(5.19、3.13、4.91),属重度、极重度污染。内梅罗综合污染指数法表明,4号和5号采样点属于极重度污染。健康风险评价模型分析表明,经口摄取途径健康风险较大,高于人体接受范围,吸入摄取途径健康风险在可接受范围内。某稀土冶炼厂周边土壤环境对人体具有一定的健康风险。     

某矿区农田土壤重金属分布特征与生态风险评价

为探明贵州六盘水某矿区周边农田土壤重金属的分布特征及污染程度,以矿区周边农田为研究对象,采集表层土壤测定Cr、Ni、Cu、Pb、Zn和As含量,分析重金属空间分布特征,评价土壤重金属污染程度及潜在生态风险,并探究其来源。结果显示,6种重金属元素含量均高于贵州省土壤重金属背景值,超标倍数依次为Cu(5.82)>Ni(2.52)>Zn(2.46)>Pb(1.81)Cr(1.51)>As(1.18),重金属分布显示矿区煤矸石山和洗选厂周边的农田土壤重金属富集较为严重。单项污染指数均值显示Cu处于重度污染水平,Ni、Zn为轻度污染水平,Pb、Cr、As为轻微污染水平;综合污染处于重度污染级别。地质累积指数法评价结果显示:Cu、Ni、Zn、Pb处于轻度污染,Cr、As表现为尚未污染水平。研究区重金属的综合潜在生态风险指数为68.02,已经达到轻度危害程度,其中Cu、Ni对综合潜在生态风险(RI)的贡献最大。多元统计分析结果显示,Zn与Pb、Zn与As以及Cu与Pb的相关性较强,表明Zn、Pb、AS、Cu的来源较相似,为第一类来源,主要源于采矿活动产生的三废;Ni、Cr分别为第二、三类来源,第二类重金属来源与汽车尾气的排放、机械损耗有关;第三类重金属主要受土壤母质影响。4种评价结果基本一致,矿区周边农田土壤重金属处于重度污染,轻度危害程度,Cu、Ni是研究区土壤影响最显著的生态风险因子,重金属主要源于采矿活动产生的三废。     

Juvenile Rats Show Reduced c-fos Activity in Neural Sites Associated With Aversion to Pups and Inhibition of Maternal Behavior.

Juvenile rats (18-23 days old) interact avidly with pups as novel stimuli and show maternal behavior after only 1-3 days of pup exposure; adults initially avoid pups and require 3-9 days of pup exposure. Upon exposure to pups as novel stimuli, adults had more c-Fos-immunoreactive neurons in the hypothalamus and amygdala--regions associated with aversion to pups--than adults exposed to familiar pup stimuli (maternal) or not exposed to pups (p     

Simplified Model of Tractive-Force Distribution in Closed Conduits

A simplified model for the computation of boundary shear stress distributions acting on the flow perimeter of closed ducts is presented. The model assumes that the surplus energy within any control volume in a three-dimensional flow will be transferred towards the nearest boundary to be dissipated. Based on this model, the flow cross sectional area in the closed duct is divided into subflow regions corresponding to the side walls and bed, and the shear distributions over the wetted perimeter within each subflow area are assessed. Analytical equations, valid for all channel aspect ratios, for the prediction of local and mean shear stresses along the bed and side walls in smooth rectangular duct flow are derived. The formulae give good predictions of the shear stress distributions when compared with existing experimental data in the literature. The possible applications of the model to nonrectangular duct flows are also discussed.