板筋结构强度计算及最优化设计

板筋结构是除尘器的重要结构形式，其结构的强度与除尘器的安全性有着密切的关系。介绍了板筋结构在除尘器应用中的荷栽、强度计算方法，并利用VB软件进行板筋结构最优化设计。     

某湖滨路拓宽改造工程的稳定性分析及处理方案研究

针对某湖滨路的拓宽改造工程,选取地基土层最不利的断面进行数值模拟,并采用强度折减法研究其整体稳定性。数值分析结果表明,加宽后的新路基稳定性较差,安全储备不能满足要求,需要采取加固措施。对初步设计提出的仅采用土工格栅和采用土工格栅+水泥搅拌桩这两种不同加固处理方案进行了数值分析。计算结果表明,相比仅采用土工格栅,采用土工格栅+水泥搅拌桩进行软基处理可以有效地减小不均匀沉降、提高路堤的整体稳定性。本文的实例研究可供类似工程参考和借鉴。     

Concentrations, sources and spatial distribution of polycyclic aromatic hydrocarbons in soils from Beijing, Tianjin and surrounding areas, North China

The concentrations, profiles, sources and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) were determined in 40 surface soil samples collected from Beijing, Tianjin and surrounding areas, North China in 2007, and all sampling sites were far from industrial areas, roadsides and other pollution sources, and across a range of soil types in remote, rural villages and urban areas. The total concentrations of 16 PAHs ranged from 31.6 to 1475.0 ng/g, with an arithmetic average of 336.4 ng/g. The highest PAH concentrations were measured in urban soils, followed by rural village soils and soils from remote locations. The remote-rural village-urban PAH concentration gradient was related to population density, gross domestic product (GDP), long-range atmospheric transport and different types of land use. In addition, the PAH concentration was well correlated with the total organic carbon (TOC) concentration of the soil. The PAH profile suggested that coal combustion and biomass burning were primary PAH sources.     

Use of silicon and ferrosilicon industry by-products (silica fume) in cement paste and mortar

With increased environmental awareness, recycling/utilization of industrial byproducts is gaining ground. One such by-product is silica fume (SF), which is byproduct of the smelting process in the silicon and ferrosilicon industry. By-products of the production of silicon metal and the ferrosilicon alloys having silicon contents of 75% or more contain 85-95% non crystalline silica. Silica fume is very useful in the design and development of high quality cement paste/mortar and concrete.This paper presents comprehensive details of the physical, chemical, properties, and its reaction mechanism. It also covers the hydration characteristics, consistency, setting times, workability and compressive strength of cement paste and mortar.     

Quantification of sources of PCBs to the atmosphere in urban areas: A comparison of cities in North America, Western Europe and former Yugoslavia

We present estimated emission source strengths of seven polychlorinated biphenyl (PCB) congeners for Banja Luka, a city that was affected by the civil war in Bosnia and Hercegovina (former Yugoslavia) in the 1990s. These emission estimates are compared to PCB emission rates estimated for the cities of Zurich, Switzerland, and Chicago, USA using an approach that combines multimedia mass balance modeling and measurement data. Our modeled per-capita emission estimates for Banja Luka are lower by a factor of ten than those for Zurich and Chicago, which are similar. This indicates that the sources of PCB emissions in Banja Luka are likely to be weaker than in the Western European and North American cities which show relatively high PCB emissions. Our emission rates from the three cities agree within a factor of ten with emission estimates from a global PCB emission inventory derived from production and usage estimates and emission factors.     

Diffuse source apportionment of the Po river eutrophying load to the Adriatic sea: assessment of Lombardy contribution to Po river nutrient load apportionment by means of an integrated modelling approach

The source apportionment of the annual nutrient load carried by the Po river to the Adriatic sea has been studied.

An integrated modelling approach was applied to the Lombardy plain area, which covers about 34% of the Po river watershed area and accounts for about 50% of the point sources’ loads carried by the river. To extract all the information available from direct instream measurements, two different modelling tools were alternatively used. The source apportionment was investigated considering both dry and wet weather scenarios. In order to quantify the apportionment in dry-weather conditions, the Lombardy portion of the Po river basin was modelled by using the US-EPA QUAL2E model. Such a simulation allowed to assess a significant contribution (about 50% of the total dry-weather load) of a not rain-driven diffuse pollution component (i.e. groundwater, springs, lake emissaries). Moreover, to estimate the rain-driven surface runoff contribution to the instream total load, the Lombardy plain area was also modelled by means of the US-DA SWAT model. SWAT results indicate a runoff contribution to the Po river instream total load of about 10 000 t N yr⁻¹ and 1300 t P yr⁻¹ (i.e. approximately the 10–20% of the total annual Lombardy nutrient load). At the event scale (i.e. the single rainstorm event) the runoff contribution may rise up to 30–80% of the total instream load. Finally, the total annual nitrogen load at the Po basin closure was estimated for the period 1985–2001. Out of a total annual load of 140 000 t N yr⁻¹, Lombardy accounts for 43% (point plus diffuse sources). The rain-driven diffuse sources constitute the 20% of the overall total load, the point sources account for 40%, whereas the remaining 40% is mainly constituted by “dry-weather diffuse sources” (i.e. groundwater, springs, lake emissaries).     

Determination of PM2.5 sources using time-resolved integrated source and receptor models

Multivariate statistical techniques are applied to particulate matter (PM) and meteorological data to identify the sources responsible for evening PM spikes at Sunland Park, NM (USA). The statistical techniques applied are principal components analysis (PCA), redundancy analysis (RDA), and absolute principal components scores analysis (APCSA), and the data evaluated are 3-h average (6–9 p.m.) PM_2.5 mass and chemical composition and 1-h average PM_2.5 and PM₁₀ mass and environmental data collected in the winter of 2002. Although the interpretation of the data was complicated by the presence of sources which are likely changing in time (e.g. brick kilns), the multivariate analyses indicate that the evening high PM_2.5 is associated with burning-activities occurring to the south of Sunland Park, and these emissions are characterized by elevated Sb, Cl⁻, and elemental carbon; 68% of the PM_2.5 mass can be attributed to this source. The PM₁₀ evening peaks, on the other hand, are mainly caused by resuspended dust generated by vehicular movements south of the site and transported by the local terrain-induced drainage flow.     

基于响应面法和强度折减法的边坡可靠性计算研究

针对边坡安全系数是隐式函数的特点,提出将有限差分强度折减法和响应面法(RSM)相结合,分析边坡可靠性的方法。采用安全系数、破坏概率及对应的临界滑动面等,作为综合评价边坡稳定性的指标。算例验证表明,笔者提出的计算方法所得结果与其他方法比较接近,且更能反映边坡真实的工作状态。对某钢铁基地工程的昔格达组地层边坡,采用新的计算方法进行可靠度分析,对比研究确定性破坏模式和概率破坏模式中剪应变增量和破坏区的分布。研究结果表明,均值强度较高的边坡岩土体,如果变异系数较大,便仍处于较高风险水平,虽然边坡整体的安全系数满足工程要求;均值安全系数和最小可靠度指标对应的破坏模式也是有差别的。     

某水电站工程右岸引水发电系统厂房后边坡稳定性三维有限元分析

针对某水电工程坝址区地质条件复杂、开挖步序多的实际情况,采用三维有限元法,分析了某水电工程右岸厂房后边坡的稳定性,得到了边坡开挖卸荷、支护中的变形规律和应力分布特性,给出边坡的破坏特征和部位,提出了边坡治理方案。引入强度折减法,以安全系数的形式来分析边坡的稳定性,强度折减法可以与边坡规范相映证,同时该方法采用边坡稳定安全系数,可以直观定性的判断边坡的整体稳定性。工程实践表明,边坡工程稳定性分析结果和加固设计方案合理有效。     

高速公路路堑高边坡施工安全风险控制研究

为避免边坡施工过程中发生失稳破坏,以广东省仁化至博罗高速公路K443+260~K443+585路堑边坡为研究对象,通过现场调查和资料收集,分析造成边坡局部滑塌的原因。运用有限元强度折减法,研究边坡进一步施工的安全稳定性和变形规律,为控制边坡安全风险提供依据。研究表明:边坡岩体裂隙发育,遇水软化,强度低是造成边坡局部滑塌的主要原因;边坡开挖过程中如果不及时支护,边坡的安全系数将下降约10%,不利于边坡的稳定。当遵循开挖一级支护一级原则时,边坡安全性可得到保证;高速公路路堑高边坡施工时采取合理安排施工工序、做好防排水措施、加强施工监控等安全风险控制措施十分必要。