中日规范中关于液化和侧向扩流场地桥梁桩基抗震设计考虑之比较

评述了我国液化场地和侧向扩流场地桥梁桩基抗震设计规范.总结了中日两国液化场地和侧向扩流场地桥梁桩基的抗震设计方法与技术细节,阐述了日本规范中液化场地和侧向扩流场地桥梁桩基抗震设计中的液化地基土反力折减系数的确定方法,以及土体液化侧向扩流对桩作用力的计算模式.指出我国规范中在液化和侧向扩流场地桩的抗震分析方法、不同土层分...     

北京市城乡环境梯度下街尘中重金属污染特征

街尘是引起城镇面源污染分布最为广泛、最重要的污染物载体.以城乡环境梯度为出发点,以北京地区的中心城区-城中村-郊区区县-乡镇-农村村庄的街尘为研究对象,并对街尘的粒径进行分级,分析城乡环境梯度下街尘的单位面积质量、粒径组成的分异规律和街尘的重金属含量及赋存形态,揭示城乡环境梯度对街尘及其负载的中重金属污染的影响和街尘中重金属污染的粒径效应,以期为我国城市化进程中街尘的源头控制和分层次管理提供科学依据.结果表明,街尘中Cr、Cu、Ni、Pb、Zn这5种重金属浓度以中心城区最高,农村村庄最低,单位面积街尘量则相反.街尘中Ni、Pb、Zn的弱酸可提取态比例较高(19.1%、11.1%、34.8%),Cr和Cu则相对较低(3.7%、2.1%).粒径<105μm街尘对重金属总量的贡献率(32.4%～62.4%)要大于其所占总质量比例(22.9%～49.6%).对重金属污染在不同城乡环境梯度可采取不同的控制策略:中心城区和郊区区县可加强细粒径冲刷的关注,而农村村庄和城中村则需加强环境卫生管理与改善道路清扫方式和频率.     

贵阳市冬季地表灰尘重金属含量动态变化及原因探析

本研究以贵阳市冬季地表灰尘和家庭燃煤为研究对象,分析了贵阳市冬季不同时段地表灰尘重金属含量的动态变化,以及家庭燃煤取暖排放的煤灰与煤尘对环境中重金属的排放影响.结果表明:贵阳市冬季前后不同时段地表灰尘重金属含量的动态变化规律为:As含量在初冬和晚冬时段均大于初春,Cu和Pb含量表现为晚冬初春初冬,Cd、Ni、Zn在3个时段的含量变化不大;冬季地表灰尘中Cd、Cu、Zn、Pb累积较重;燃煤中元素As、Cd、Pb、Zn主要富集于煤尘中,Ni、Cu则主要富集于煤灰中.贵阳市地表灰尘在晚冬、初春时段,细粒级灰尘所占质量占比明显高于初冬,而且晚冬灰尘中粗粒级所占质量比最低,3个时段中,晚冬时段灰尘中大部分重金属含量随粒级减小而增大的特征表现得最明显.家庭燃煤排放对地表灰尘中的As、Pb含量有一定的影响.     

Research on the influence of foaming gas in compressed air/nitrogen foam on extinguishing the n-heptane tank fire

Tank fires threaten the lives of people and pollute the environment for their intense radiant heat, rapid fire spread and explosion hazard. Compressed air/nitrogen foam (CAF/CNF), a cleaner fire extinguishing technique used for the tank fire suppression because halogen-based agents were prohibited for environmental reasons. In this work, the influence of foaming gas in CAF/CNF on extinguishing the n-heptane tank fire was firstly investigated. Firstly, it was found that CNF spreads faster with rapid increase in foam thickness, mainly due to its better stability and less evaporation. Secondly, after foam was discharged, there existed a short increase of the combustion intensity, associated with three monotonous regions and two time delays in the whole extinguishing time. The two time delays were caused by Rayleigh–Taylor instability and flame sheet shift, respectively, and the shift distance was larger for CNF. Finally, the influential factors contributing to flame extinction were exhibited to be mainly related to the decrease in liquid burning rate and gas-phase Damkohler number. Among these factors, foam spreading rate and thickness dominated due to coupled chemical and physical extinguishing effects. Resulted from some competitive effects, CNF was slightly more efficient at extinguishing tank fires than CAF.     

街道峡谷对近地层风场影响的观测和模拟分析

城市街道峡谷结构对近地面边界层的风场环流等气象要素具有重要影响,可导致城市局地空气污染分布发生变化.随着城市化发展及城市空气质量变化,街道峡谷的城市空气污染影响日益突出,分析街道峡谷内部风场成为认识和治理我国城市空气污染的一条重要途径.鉴于目前我国鲜有城市街道尺度大气边界层精细气象观测研究,本文分析了美国俄克拉荷马大学的街道峡谷精细气象观测数据及其FLUENT模拟.结果表明:街道峡谷内风场结构变化依赖大气背景风向,当背景风向平行于街道峡谷走向时,街谷两岸风速几乎没有差异,而在背景风向垂直于街道峡谷走向时,由于高空风进入街谷形成的涡旋气流对街道峡谷风场有补充作用,峡谷两侧中层高度风场差异变大,风速差值大约为0.5 m·s~(-1),且街道峡谷两岸风速差异得到了FLUENT模式的验证,但模式对迎风岸的风速模拟存在高估,模拟的中层高度处两岸风速差值为1.6 m·s~(-1).观测资料分析揭示大气边界层稳定度条件对街道峡谷内风场分布也有很大影响,中性稳定条件下街道峡谷两岸近地层风速差异最大,输送进入峡谷空间的风速增量比原峡谷内风速大约高1倍,其它稳定度条件下街谷两岸风速差异被削弱.     

三峡库区生态环境与农业持续发展

三峡库区系指出从重庆到宜昌段为水库波及的２０个县市。该区属川东陵谷区，以山地丘陵为主，河谷平坝比重小，种植业垂直分异明显，海拔５００ｍ以下的三熟制区，８００￣１４００ｍ为一熟制区，两区间系两熟制区。     

北京市地面街尘与径流中重金属的污染特征（Characteristics of Heavy Metals in Street Dusts and Urban Runoff in Beijing）

街尘作为城市各种污染物的载体和地表径流污染物的主要来源对水环境的影响日益受到关注.论文分析了北京市城区街尘与地表径流中重金属浓度和颗粒的粒径分布.结果表明:不同城市土地利用类型对街尘和径流中的重金属含量、颗粒粒径分布具有重要影响.在商业区、主要道路、住宅区、城中村4种土地利用类型中,街尘重金属浓度和地面单位面积重金属质量均以主要道路最高;径流重金属浓度由高到低顺序依次为:主要道路>城中村>居民区;主要道路和商业区街尘颗粒中细粒径占的比例较高,在全部土地利用类型的径流水样中颗粒物粒径分布差别不大;随着街尘中颗粒物粒径的减小,重金属浓度增加;街尘中小于149μm的颗粒物质量百分比和重金属浓度均较高,且在径流中这个粒径段的颗粒物含量也高,体积比达80%以上.建议在今后的城市街尘面源污染控制中应特别关注土地利用类型和街尘粒径的影响.     

步行街在城市地下综合体中防火分隔的应用

城市地下综合体在大型城市中迅猛发展,而现行防火规范中对其商业部分防火分隔的要求难以满足设计需求。结合城市地下综合体的建筑特点,提出将采取加强消防设计的步行街作为防火分隔的措施,以某城市地下综合体为例,通过理论分析与数值模拟的方法,证明了该防火分隔方案能够达到现行防火规范要求的分隔效果。     

SIMULATION OF URBAN NON-POINT SOURCE POLLUTION1

ABSTRACT: Public Law 92–00 has mandated the need for evaluating the impact of nonpoint source pollution on receiving water quality, primarily through Section 208 Areawide Planning. The Management of Urban Non-Point Pollution (MUNP) model was developed to estimate the accumulation of eight non-point pollutants on urban streets, their removal by both rainfall and street sweeping operations. The model can simulate the following pollutants: total solids or sediment-like material, volatile solids, five-day biochemical oxygen demand, chemical oxygen demand, Kjeldahl nitrogen, nitrates, phosphates, and total heavy metals. The simulated results can be used for investigation of non-point pollution management alternatives. The model is capable of reflecting variation in such diverse factors as physical and chemical characteristics of accumulated pollutants, land use characteristics, rainfall characteristics, street sweeper characteristics, roadway characteristics, and traffic conditions. By using mean estimates of many input variables for large segments of a city, the MUNP model could be used to quickly assess the magnitude of pollutants annually entering receiving waterways due to nonpoint source pollution alone. If the results indicate that non-point pollution loadings are sizeable and require futher analysis, the MUNP model could be used to define the specific nonpoint source pollution areas within a city. Hypothetical locations and actual rainfall data for Washigton D.C. were used to demonstrate some capabilities of the MUNP model.     

AQUATIC IMPACTS OF DEICING SALTS IN THE CENTRAL SIERRA NEVADA MOUNTAINS,CALIFORNIA1

ABSTRACT: The fate and effect of sodium chloride applied to Californian highways in the Lake Tahoe, Truckee River, and Yuba River watersheds were studied over a period of 14 months in 1974–75. Chloride levels in streams below major freeways were found to be elevated during the winter. The high chloride levels occurred after the application of salt to roads, decreasing as the time from application increases. Small lakes receiving runoff from major highways were also enriched with chloride. Several of these lakes displayed a temporary chemocline, which was sufficiently strong to stabilize a temperature inversion in one lake.