潮流作用下桥墩局部冲刷规律研究

桥墩局部冲刷深度的可靠预测是保证桥梁安全运行的基础。我国对河流上的桥墩局部冲刷做过大量研究,但河口海湾及沿海地区跨海湾桥梁,往往水域宽阔,作用水流多为极其复杂的双向潮流,目前针对性的研究尚少。通过对钱塘江河口及杭州湾的嘉绍大桥、杭州湾大桥和金塘大桥在潮流作用下的桥墩局部冲刷开展水槽试验,研究了桥墩在潮流作用下的冲刷坑形态与冲刷过程,并对潮流作用下桥墩局部冲刷深度的主要影响因子进行了分析。     

跨海桥梁基础冲刷特征研究

在我国近海海域,跨海桥梁基础冲刷是影响大桥安全的重要因素之一。基于金塘大桥2014、2015和2017年桥墩基础冲刷实测资料,并结合建桥前地形测验资料进行了案例分析,解析出了往复潮流条件下桥墩基础的一般冲刷及局部冲刷深度,金塘大桥中引桥桥墩一般冲刷深度为3.3~3.6 m,平均局部冲刷深度约8.3 m。往复潮流条件下桥墩基础局部冲刷坑受双向潮流影响向上下游延伸,形状呈椭圆形,各墩冲刷坑纵向长度与最大局部冲刷深度呈近似线性关系,长度约为局部冲刷深度的10~12倍,而各墩冲刷坑横向宽度则基本一致,约为桥墩基础宽度的4~5倍,与最大局部冲刷深度无明显相关性。跨海桥梁基础冲刷深度计算方法及冲刷坑形态特征的研究成果可供跨海大桥基础设计、运行维护及基础冲刷防护参考。     

潮流作用下复合桥墩局部冲刷研究

桥墩冲刷是桥梁水毁的重要原因之一,准确地计算桥墩冲刷深度具有重要意义.为了比较准确地计算桥墩局部冲刷深度,结合某跨海大桥,采用非结构网格技术和大、小模型嵌套的方法建立该大桥海区的平面二维潮流数学模型,采用潮位、流速、流向等实测资料进行验证.在此基础上,对该海区的潮流动力进行了模拟研究,分析了大桥工程对周围海域的潮流动力影响,并采用我国行业标准推荐的2种公式以及美国现行规范推荐的公式计算多座跨海大桥桥墩的局部冲刷计算.结果表明:大桥工程对桥区附近水域流速和潮位影响不大,桥墩可能发生最大局部冲刷深度的位置均位于主墩深槽附近.     

桥墩基础局部冲刷计算方法的对比研究

桥墩基础局部冲刷深度是确定基础埋深和保证桥梁安全运营的重要参数。针对桥墩基础局部冲刷深度不同的计算公式在量纲和谐、一般冲刷深度及河床形态和床沙组成对局部冲刷深度的影响进行对比分析,并结合工程算例,对计算结果进行对比。研究表明:对于单墩桥墩,HEC-18公式和包尔达柯夫公式计算较为简便,且HEC-18公式的计算结果偏安全;对于复杂群桩承台桥墩,中国铁道科学研究院新公式比较规范,采用公式所考虑的因素更多,结果更安全。     

桥墩局部冲刷分析及防护对策

河道中修建桥墩后，周围的水流情况会发生很大变化，从而引起桥墩周围产生局部冲刷。桥墩附近水流结构十分复杂，对于重要的工程问题，主要依靠物理模型试验分析局部冲刷。目前，国内外关于桥墩局部冲刷深度的计算方法主要有：非黏性土河床的桥墩局部冲刷公式，黏性土河床桥墩局部冲刷公式以及适用于黄河的冲刷计算公式。在确定冲刷深度后，进一步分析了桥墩基底埋置深度。同时，总结了浅基防护工程的几种类型。     

砂质河道桥墩局部冲刷计算经验公式改进和验证

桥墩局部冲刷深度是桥梁设计的重要参数，但随着造桥技术的发展，桥墩局部冲刷计算的经验公式在计算尺寸较大的桥墩局部冲深时误差偏大。为解决此问题，在前人的研究基础上，根据统一量纲的原则建立了砂质河道桥墩局部冲刷深度经验公式，并考虑基台露出床面对冲刷的影响，对公式进行修正。将文中提出的公式与中美计算规范进行比较，结果表明：所提出的公式具有考虑因素较全面、量纲统一、适用于大型桥墩局部冲刷深度计算的优点；计算精度相比另外3种公式有较明显的提高，能更好地预测桥墩局部冲刷深度。研究成果可为桥墩布设、施工与防护等提供技术支撑。     

桥墩局部冲刷公式研究进展

总结国内外桥墩局部冲刷的研究成果,分类列举了单向流情况下非黏性土桥墩的局部冲刷公式;对比讨论了中国、前苏联及美国关于桥墩局部冲刷的规范公式。介绍了受潮流作用的桥墩和黏性土桥墩冲刷的最新研究进展。     

基于量纲分析的宁波象山港大桥桥墩局部冲刷规律研究

针对宁波象山港大桥桥墩冲刷严重问题,为了剖析潮流径流共同作用下跨海大桥复式桥墩局部冲刷机理,科学预测桥墩局部冲刷规律,通过系统分析、评估、复核象山港大桥相关试验成果和现场实测数据,深入研究了象山湾内关键水文泥沙参数(波浪、潮流、潮位、泥沙量、海底冲刷)变化特征,利用主因子分析及量纲分析等手段,建立象山港大桥桥墩局部冲刷公式,并利用观测数据进行验证。研究表明,象山湾内各涨急落急流速变化不大,涨急和落急之间差别明显。涨急和落急时的代表垂线平均流速分别为-1 m/s和1.14 m/s,且涨落急时刻对应的代表潮位分别为1.37 m和0.54 m。针对象山港大桥桥墩特性分别建立三类桥墩局部冲刷公式,计算得到的预测值与观测值误差在±5%以内,说明所提出的预测公式具有较好的预测效果,能有效地揭示象山港大桥的冲刷规律。     

基于量纲分析的宁波象山港大桥桥墩局部冲刷规律研究

针对宁波象山港大桥桥墩冲刷严重问题，为了剖析潮流径流共同作用下跨海大桥复式桥墩局部冲刷机理，科学预测桥墩局部冲刷规律，通过系统分析、评估、复核象山港大桥相关试验成果和现场实测数据，深入研究了象山湾内关键水文泥沙参数( 波浪、潮流、潮位、泥沙量、海底冲刷) 变化特征，利用主因子分析及量纲分析等手段，建立象山港大桥桥墩局部冲刷公式，并利用观测数据进行验证。研究表明，象山湾内各涨急落急流速变化不大，涨急和落急之间差别明显。涨急和落急时的代表垂线平均流速分别为－1 m /s 和 1. 14 m /s，且涨落急时刻对应的代表潮位分别为 1. 37 m 和 0. 54 m。针对象山港大桥桥墩特性分别建立三类桥墩局部冲刷公式，计算得到的预测值与观测值误差在±5%以内，说明所提出的预测公式具有较好的预测效果，能有效地揭示象山港大桥的冲刷规律。     

大桥复合桥墩局部冲刷深度的计算分析

桥墩的冲刷毁坏是桥梁失事的重要原因。为保证桥梁安全,需要准确评价桥墩冲刷深度。本文结合某跨海大桥,使用较为可靠的HEC-18公式对其复合桥墩的局部冲刷深度进行研究。计算结果表明,该大桥最大的可能局部冲刷深度发生在主桥主墩,复合桥墩中群桩部分造成的冲刷深度为桥墩冲刷的主要部分,且随流速增大,其在总冲刷深度中所占比例也增大,总冲刷深度对承台吃水深度变化不敏感。进一步分析表明,复合桥墩的冲刷深度随水流斜交角的变化规律与简单桥墩有较明显区别,关系更为复杂。     

地下厂房施工过程的三维非线性数值模拟分析

根据冗各电站地下厂房开挖支护的施工顺序,以隐式杆单元模拟锚杆,以壳单元模拟混凝土喷层,采用三维非线性有限元技术,对洞室群的开挖支护动态过程进行了模拟计算。通过三维非线性有限元计算分析得到:洞室群动态开挖过程中围岩应力变形的分布规律,围岩塑性区的发展规律,锚杆受力变化情况。计算结果表明:整个开挖过程中,洞周围岩位移变化规律正常,量值较小,塑性区主要分布在洞室周边,围岩稳定性较好;但在洞室交叉口处围岩的变形较大,出现较大范围的塑性区,在此基础上提出了支护措施优化方案,并对优化方案的效果进行了评价。     

Evaluation of freshwater mussel relocation as a conservation and management strategy

The relocation of unionacean mussels is commonly used as a conservation and management tool in large rivers and streams. Relocation has been used to recolonize areas where mussel populations have been eliminated by prior pollution events, to remove mussels from construction zones and to re-establish populations of endangered species. More recently, relocation has been used to protect native freshwater mussels from colonization by the exotic zebra mussel Dreissena polymorpha. We conducted a literature review of mussel relocations and evaluated their relative success as a conservation and management strategy. We found that 43% of all relocations were conducted because of construction projects that were forced to comply with the Endangered Species Act 1973 and that only 16% were monitored for five or more consecutive years. Most (43%) relocation projects were conducted from July to September, presumably a period when reproductive stress is relatively low for most species and the metabolic rate is sufficient for reburrowing in the substrate. The mortality of relocated mussels was unreported in 27% of projects; reported mortality varied widely among projects and species and was difficult to assess. The mean mortality of relocated mussels was 49% based on an average recovery rate of 43%. There is little guidance on the methods for relocation or for monitoring the subsequent long-term status of relocated mussels. Based on this evaluation, research is needed to develop criteria for selecting a suitable relocation site and to establish appropriate methods and guidelines for conducting relocation projects.     

基于模型试验的河床砂砾石层基本特性研究

为了经济可靠地确定深厚覆盖层的基本特性参数,以大渡河双江口水电站坝基河床砂砾石层基本特性研究为工程背景,进行大尺寸模型试验,研究河床砂砾石层的旁压模量和动探击数随密度、级配以及上覆压力的变化规律。根据室内模型试验结果,结合现场旁压试验及钻孔试验成果,推断出坝址区河床砂砾石相关层位的密度,并依此进行砂砾石室内力学试验,获得设计所需力学参数。研究成果可为深厚覆盖层基本特性测试提供新的方法。     

Serial discontinuities in a Rocky mountain river. I. Distribution and abundance of plecoptera

Samples were taken year-round at eleven sites along the altitudinal profile (2900-1400 m a.s.l.) of the Gunnison River, a 329 km tributary of the Colorado River, to document the distribution of the Plecoptera and to evaluate responses to hypolimnial-release dams in the headwaters and middle reaches. Twenty-two species were present, with the greatest species richness occurring in an unregulated segment upstream of the middle reach dams; average nymphal biomass over the study period (175 organisms, 395 mg dry mass m^?2) was also greatest in this segment. Only four species (58 organisms, 48 mg m^?2) were present in the tailwaters of the headwater dam and values were greatly reduced (nine species; 35 organisms, 180 mg m^?2) below the middle reach dams. The stonefly community recovered ca. 80 km downstream from the last dam (15 species; 244 organisms, 250 mg m^?2), apparently in response to natural resetting of environmental conditions corresponding to those above the middle reach dams. At the most downstream site (11) only four species (four organisms, 16 mg m^?2) were present. The observed distributional pattern is a classic serial discontinuity in response to hypolimnial stream regulation in a temperate latitude river.     

基于BP神经网络-马尔科夫链模型的隧道围岩位移预测

在隧道工程施工中,围岩位移预测起着很重要的作用。将BP神经网络-马尔科夫链模型引入到隧道围岩位移预测中来,通过对训练样本的学习,利用BP神经网络实现了对位移时间序列的滚动预测,同时得到了实测值与预测值的相对误差;在此基础上利用马尔科夫链对相对误差进行修正,有效地提高了预测结果的精度。并将该模型应用于某公路隧道拱顶下沉位移时序预测中,结果表明该模型具有精度高、科学可靠的特点,为隧道围岩变形的预测提供了新的途径。     

Short communication. Pipelines as a refuge for freshwater snails

In the lower River Murray, Australia, populations of gastropods have declined markedly over the past 40 years. Of the native fauna of about 18 species, only the ancylid Ferrissia petterdi remains common (but in patches), and another five species feature in sporadic local resurgences. Until recently the viviparid Notopala was thought to be extinct. The introduced physid Physa acuta is widespread, but in low numbers. The decline probably is associated with flow regulation, high turbidity and the introduction of common carp. Snail populations have persisted, however, in irrigation pipelines fed from the river, where they periodically cause blockages. This paper reports the discovery of the only known populaion of Notopala hanleyi in a pipeline where the inner wall accumulates microbial and other organic matter, providing high quality food for snails. In the Murray before regulation most of the periphytic biomass was probably microbial, as fluctuating water levels would have maintained littoral communities in a highly productive, early state of succession his postulated that, by stabilizing seasonal water levels, regulation has promoted the production of filamentous green algae, an inferior food source, and so displaced snail populations from the open aquatic environment.     

浙江省水域调查录入系统的设计和应用

浙江省水域调查录入系统将调查数据与电子地图相整合,对分类水域数据进行统计计算,并对输入数据进行合理性和完整性检查,得到调查范围内现有水域的详细数据,实现了水域调查数据输入、计算、统计和查询的数字化管理,提高了工作效率和工作质量,为各地下阶段水域保护规划编制和水域管理工作提供了数据支持。对该系统的设计原则、功能和技术设计等作了介绍。     

基于CT-连续加荷水泥乳化沥青混凝土细观损伤规律研究

利用CT技术对水泥乳化沥青混凝土的细观损伤过程进行实时扫描观测,获得了混凝土试件在连续加荷下的CT图像。通过采用直观分析法、CT数分析法、CT数与损伤变量关系3种方法分析表明,水泥乳化沥青混凝土的破坏过程可分为压密、扩容、裂纹扩展、破坏4个阶段,同时混凝土在受压过程中具有韧性,在极限荷载之前各断面处于压密和微扩容的强化阶段,极限荷载之后混凝土从损伤到破坏发展比较平稳。     

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.