斜墙背挡土墙后大主应力拱及被动土压力分析

根据莫尔应力圆,研究墙背倾斜、粗糙的挡土墙墙背土体在被动状态下,主应力方向和应力比值的变化;对墙后大主应力拱进行理论分析,确定挡土墙的被动侧土压力系数;利用水平微分单元法,计算挡土墙的被动土压力.结果表明,墙背变缓时,墙背土体的小主应力方向逐渐趋近于竖直,其垂直应力减小,水平应力增大;大主应力拱为上凸曲线;被动土压力呈曲线分布,合力作用点高度随墙背坡角而变,合力与库仑解相等.     

挡土墙背摩擦角为负的被动土压力研究

目前大多数被动土压力问题研究的是挡土墙背摩擦角为正的情况(墙身相对土体向下移动)，而挡土墙背摩擦角为负(墙身相对土体向上移动)的被动土压力问题则研究的较少。在平面滑裂面假设的基础上，利用散粒体Kötter方程通过极限平衡分析得到了挡土墙背摩擦角为负时的被动土压力系数、被动土压力合力和被动土压力合力作用点高度的理论公式。分析了挡土墙倾角、填土内摩擦角、填土坡角和墙背摩擦角对被动土压力系数、土压力合力作用点高度的影响。与挡土墙背摩擦角为正不同的是，墙背摩擦角为负时随摩擦角的增加，被动土压力系数减小。用图形和表格的形式给出了相应的结果，可为锚、输电线路基础受上拔荷载时设计所采用。     

RT位移模式挡土墙非极限被动土压力探讨

利用土体摩擦角的发挥值和准滑移面概念,探讨RT位移模式挡土墙非极限状态被动土压力。研究表明,RT位移模式挡土墙非极限状态被动土压力呈凹曲线分布,越靠墙底被动土压力增大越快,土压力合力随墙体位移增大而增大,其作用点在墙高的下三分点以下,随墙体转动位移增大而逐渐降低。     

地震条件下挡土墙被动土压力及其分布的微分薄层计算方法

基于微分薄层法思想推导出被动土压力沿挡土墙墙高的非线性分布公式,研究了地震条件下分层土挡土墙被动土压力的计算方法。文中以墙后均匀填土挡土墙为例计算被动土压力,经与朗肯、库伦土压力理论公式的计算结果比较,有很好的吻合性。文章对被动土压力的分析和计算方法,突破了以往所研究的解析解均是针对单一、均质、各向同性填土的限制,可适用于多层不同性质填土的挡土墙被动土压力的计算。而文章计算得到的被动土压力合力的作用点位置低于朗肯、库伦被动土压力合力作用点位置,与以往多位学者相关研究的结论一致,也应该引起注意。     

挡土墙背摩擦角为负的被动土压力研究

在平面滑裂面假设的基础上,利用散粒体Ktter方程通过极限平衡分析得到了挡土墙背摩擦角为负时的被动土压力系数、被动土压力合力和被动土压力合力作用点高度的理论公式。分析了挡土墙倾角、填土内摩擦角、填土坡角和墙背摩擦角对被动土压力系数、土压力合力作用点高度的影响。与挡土墙背摩擦角为正时不同,墙背摩擦角为负时随摩擦角的增加,被动土压力系数减小。用图形和表格的形式给出了相应的结果,可为锚、输电线路基础受上拔荷载时设计所采用。     

RB位移模式挡土墙非极限状态被动土压力研究

针对绕墙底转动模式挡土墙,在无黏性填土和填土表面水平条件下,考虑填土内摩擦角的发挥程度和土压力系数的变化,采用水平层分析法,研究该(0.31~0.36)模式挡土墙非极限状态被动土压力。研究表明:绕墙底转动模式的挡土墙非极限状态被动土压力近似呈折线分布,合力作用点到墙底的距离为(0.31~0.36)倍墙高。     

考虑土拱效应的挡土墙被动土压力分析

基于库伦土压力理论,假定被动极限状态下挡土墙后大主应力拱迹线为抛物线,考虑土拱效应,推导了被动土压力系数的理论公式,并将其用于水平微分单元法,分析土体处于被动极限平衡状态时的应力状态,得到平动模式下被动土压力强度、合力及合力作用点的计算公式;在此基础上,分析了内摩擦角及墙面摩擦角对被动土压力系数、土压力强度及合力作用点的影响,并与库伦土压力理论等已有方法和模型试验数据进行了对比分析,验证了该计算方法的合理性。     

悬臂式挡土墙主动土压力计算

在水利工程中,悬臂式挡土墙是钢筋混凝土挡土墙的主要形式,组成部分包括立板和底板。因此,对悬臂式挡土墙主动土压力计算问题,就是施工设计中必须要考虑的问题。文章针对填土表面水平且无粘性的条件下,通过水平微元法推求悬臂式挡土墙后出现三角形滑动土楔时的主动土压力,得到主动土压力合力作用点高度以及主动土压力沿墙高分布的变化规律。     

绕墙底转动挡土墙非极限状态主动土压力计算

挡土墙绕墙底背离土体转动时,墙背各点的位移不同,相应位置的土体内摩擦角发挥值不同,据此研究绕墙底转动位移模式挡土墙非极限状态主动土压力的计算。结果表明,绕墙底转动位移模式挡土墙非极限状态主动土压力呈凹曲线分布,墙顶位移增大,土压力系数和土压力整体减小,合力作用点降低,均在墙高的下三分点以下。     

平移模式挡土墙非极限状态被动土压力有限元分析

采用有限元方法,就挡土墙平移挤压土体被动非极限状态的土压力进行研究。结果表明,墙背附近土体形成近似倒梯形的相对位移区,区内相邻点之间存在水平位移差和竖向位移差,相对位移区水平长度(2~3)墙高,墙体位移越大,相对位移区越大。挡土墙平动模式非极限状态被动土压力的分布近似直线。土压力由静止状态过渡至被动极限状态时,水平被动土压力总值增长速率逐渐减缓,其值始终小于库伦被动土压力。填土摩擦角越大,非极限状态被动土压力越大。     

SPATIAL AND TEMPORAL WATER QUALITY VARIABILITY IN AQUATIC HABITATS OF A CULTIVATED FLOODPLAIN

The floodplains of lowland rivers contain diverse aquatic habitats that provide valuable ecosystem services but are perturbed when intensively cultivated. Hydrologic, water chemistry and biological (fish) conditions in five aquatic habitats along the Coldwater River, Mississippi, were measured for more than 4 years: the river, two severed meanders that functioned as backwaters, a managed wetland and an ephemeral channel draining cultivated fields. Off‐channel habitats were connected to downstream regions 0.10% to 32% of the dry season and 24% to 67% of the wet season. The median temperatures for the five monitored sites ranged from 18°C to 23°C, the median total solids concentration for all sites was 135 mg L^?1, the median total phosphorus was 0.29 mg L^?1 and the median total nitrogen was 1.56 mg L^?1. Chemical and physical water quality displayed strong seasonal differences between the wet winter/spring and the dry summer/fall periods so that temporal variation consisted of gradual seasonal trends superimposed on strong diurnal variations. All off‐channel habitats exhibited periods of hypoxia and temperatures >30°C during the dry season. Between‐site gradients of water and habitat quality were strongly coupled to water depth and runoff loading. The rehabilitation of one backwater by increasing water depth and diverting agricultural runoff was associated with improved water quality and fish species richness relative to an adjacent untreated backwater. The diversion of polluted runoff and the use of water control structures to maintain greater water depth were observed to be effective management tools, but the former reduces the water supply to habitats that tend to dry up and the latter reduces connectivity. Published in 2011 by John Wiley & Sons, Ltd.     

Automated system for removal and pneumatic transport of fly ash from electric precipitator hoppers

A system for removal and pneumatic transport of fly ash is examined, in which air pulses act on batches (pistons) of ash formed in a duct. Studies are made of the effect of several physical parameters on the force required to displace a piston of ash and these serve as a basis for choosing a system for removal and pneumatic transport of ash simultaneously from several hoppers of an electric precipitator. This makes it possible to separate the ash particles according to size without introducing additional components. Formulas are given for calculating the structural and dynamic parameters of this system and measurements of indirect dynamic parameters are used to calculate the input-output characteristics of the system. In order to optimize the system, configurations for summing several ducts into a single transport duct for pneumatic ash transport are proposed. Some variants of dry ash utilization and the advantages of producing of size-separated particles are considered. __________ Translated from élektricheskie Stantsii, No. 2, pp. 26–30 (2008).     

The flood pulse advantage and the restoration of river-floodplain systems

The ‘flood pulse advantage’ is the amount by which fish yield per unit mean water area is increased by a natural, predictable flood pulse. Evidence for this increase is presented from tropical and temperate fisheries. It is argued that increasing multispecies fish yield by restoring the natural hydrological regime is consistent with increasing production of other trophic levels and with restoration from ecological and aesthetic viewpoints. When applied to a river-floodplain system, this restoration would provide a large, self-sustaining potential for recreation, commercial exploitation, and flood control. An interim ‘natural flood pulse’ restoration approach is proposed for systems modified for navigation. This approach approximates the natural hydrological regime in a river reach and is intended as a first step in the long process of restoring the watershed.     

岩石动态拉伸断裂特性的实验研究

采用新近发展起来的拉伸式Ｈｏｐｋｉｎｓｏｎ冲击装置（ＳＨＴＢ），对岩石切口圆柱断裂试样进行了动态拉伸断裂特性的实验研究。同时，利用ＭＴＳ试验机进行了岩石的静态拉伸断裂实验，成功地获得了岩石试样的断裂韧度及断裂能随加载率而变化的实验结果。对静态和动态破坏后的试样断口进行的扫描电镜观察进一步表明，试样断口形貌的复杂程度与其断裂耗能有着十分密切的联系。     

Spatio‐temporal variation of gross CO2 and CH4 diffusive emissions from Australian reservoirs and natural aquatic ecosystems,and estimation of net reservoir emissions

Carbon dioxide (CO₂) and methane (CH₄) diffusive emissions were measured during two field surveys in Queensland and Tasmania, Australia, using the floating chamber method. Bubbling and degassing emissions in 2010 were estimated in Koombooloomba Dam reservoir using only inverted funnels and gas concentrations, respectively. A total of 14 reservoirs and 16 rivers and lakes were sampled from 2006 to 2010. Spatial variation was substantial within each water body, as well as between them. The main drivers of diffusive emission variation were physiographic region and climate, with a clear demarcation being observed between diffusive emissions from tropical Queensland and temperate Tasmania, and between the humid West Coast Range (Tasmania) and dry Central Plateau (Tasmania). Higher CO₂ and CH₄ diffusive emissions were observed during the dry season, when long water residence times would promote organic matter degradation. Estimated total gross emissions, including diffusive, bubbling and degassing emissions, for Koombooloomba Dam reservoir were about 1.5 × 10⁶ t CO₂eq km² per year, or 24 × 10⁶ t CO₂eq per year. This corresponds to a plant emission factor of 3.18 kg CO₂eq MWh^?1. Using an estimate of terrestrial emissions derived from literature data for the Tully River catchment area, rough estimated net emissions from the catchment area are about 44 kt CO₂eq per year, or 5.83 kg CO₂eq MWh^?1, which is in the lower range of the studied reservoirs.     

Comparative analysis of glacial and nival streamflow regimes with implications for lotic habitat quantity and fish species richness

Growing interest in the differential responses of glacial and nival rivers to climatic forcing, and in ecological distinctions between the two streamflow regimes, suggests the need for a better comparative understanding of how the annual hydrologic cycle differs with presence or absence of catchment glacial cover. In this study, timing and magnitude characteristics of the average annual hydrographs of five glacierized and four nival catchments in the southwestern Canadian subarctic are empirically identified and compared. Likely effects upon fish habitat are qualitatively assessed, and net fisheries potential is tentatively investigated using taxa richness data. The chief hydrological conclusions at P < 0.05 using Kolmogorov–Smirnov and empirical orthogonal function analyses are: (1) catchment glacial cover results in freshets that are longer, larger, and peak later than those experienced by the nival regime; (2) the winter baseflows of glacial rivers are also much higher on a unit‐catchment‐area basis; and (3) basin scale and degree of catchment glacial cover are of comparable importance in determining the magnitude of the annual hydrologic cycle. These differences arise from the greater availability, both in volume and over time, of meltwater in glacial catchments, which in part reflects the consistently negative alpine glacial mass balances observed both in the present study area and globally under historical climatic warming. Such regime distinctions result in increased spawning season and winter aquatic habitat availability, which may in turn offset negative habitat characteristics previously identified for glacial river ecosystems. While previous studies have suggested that glacial influences tend to decrease macroinvertebrate diversity and increase salmon populations, preliminary analysis of available fish species presence/absence data from the current study area tentatively appears to suggest similar or, perhaps, slightly higher fish taxa richness relative to nival streams; in all three cases, however, catchment lake cover may play a key hydroecological modifying role. The results strongly confirm and extend existing understanding of glacial–nival regime differences with respect to both streamflow and fisheries ecology, and raise new questions for future research. Copyright © 2005 John Wiley & Sons, Ltd.     

POS系统及其在航空摄影中的应用

描叙了POS系统的运行原理,并结合原理分析了POS系统在航空摄影应用时应该注意的偏心分量测量、POS设备初始化、数据精度控制及基站架设等问题,最终结合实际的航摄飞行要求对POS系统在实际航空摄影中出现的上述问题提出预防措施和解决办法。     

Lake Turkana,major Omo River developments,associated hydrological cycle change and consequent lake physical and ecological change

This study aimed to explore Lake Turkana's ecological reliance on hydrology and to determine the hydrological changes and consequences arising from the major hydropower and irrigation developments in the lake's basin. The major developments on Ethiopia's Omo River are especially significant as this river provides over 80% of the lake's annual freshwater influx and associated nutrients. The cascade of hydropower dams permanently dampens the natural hydrological cycles and lake level variability. The driving force of the flood influx to the lake is curtailed and the pattern of lake currents will adjust. Ultimately 80% of the river inflow to the lake will be regulated. Large volumes of water are required to initially fill the hydropower dam reservoirs. During 2015–16 when the huge Gibe III reservoir was filled, Lake Turkana's water level declined 2?m.The study has shown that large-scale irrigation schemes in the Lower Omo can potentially abstract 50% of the Omo River water, and that this would cause the lake level to shrink permanently to the detriment of the lake ecology. Possible lake level drops of over 15?m are demonstrated. The basin's natural capital is being replaced by large-scale plantation developments. The hydrological changes are drastic and the ecological consequences on Lake Turkana have not been fully understood. Without serious mitigation measures, Lake Turkana is a potential African Aral Sea disaster in the making, emulating what has happened to other great lakes such as Lake Chad.     

天生桥一级水电站混凝土面板堆石坝位移监测

天生桥一级电站混凝土面板堆石坝的填筑坝体位移监测通过水管式沉降仪和水平位移计进行。坝本内安装了５０支水管式沉降仪（瑞曲盒式）、３１支水平位移计（钢丝型伸缩仪）和２８支总压力计。监测结果表明，施工期末（１９９９年３月）最大坝体沉降是２．９４ｍ，相当于坝体高度的１．７％，施工期末堆石坝变形模量Ｅｒｃ平均４５ＭＰａ，为最大坝体变形，促使上游边坡出现裂缝以及面板浇筑前上游边坡明显沉降。     

On Some Kinds of Damage in Drums of High-Pressure Boilers

Kinds of damage in drums of high-pressure powerplant boilers in the places of welding of separation devices by austenite electrodes are described. Results of a complex study of damaged metal are presented. The mechanism of damage caused by contact (electrochemical) corrosion on the interface of two metals with different values of electrode potential is established. Measures for preventing the described kinds of damage are recommended.