管涌型土滤层防治的细观试验研究

利用数码可视化跟踪技术、计算机信息实时处理技术和土体变形无标点量测技术,从细观层面上对不同层间系数的宽级配基料-滤层系统进行了渗透模型试验。从细观角度分析了不同层间系数的砂样在渗流过程中的水力特性、颗粒运动特点和系统破坏特征,研究了滤层的特性和管涌型土自滤自稳定的细观机理。结果表明:层间系数D15/d85s是决定滤层是否合格的最关键因素,随着比率D15/d85s的增大,系统朝不稳定的方向发展;越靠近上游的颗粒移动的越早,越小粒径的颗粒潜在的移动距离越大;除了层间系数,加压速率和扰动力等因素也会影响管涌的发生发展。     

砂土管涌－滤层防治的离散元数值模拟

结合小比尺细观模型试验,利用并开发基于离散元理论的颗粒流程序(PFC3D),充分考虑流固耦合作用,建立渗流理论模型,对不同层间系数下砂土管涌的基料-滤层系统进行离散元数值模拟,跟踪记录渗流过程中砂样运动、流失量、孔隙率、渗透系数、颗粒间接触力、水力梯度等参数的动态变化过程,从细观角度揭示管涌发展过程中颗粒的运动特性和滤层防治机理。数值模拟结果表明,层间系数D15/d85s大小是滤层是否有效的关键因素;在有效的层间系数下,随着水力梯度的加大,基料的细颗粒运动并进入滤层,在滤层-基料交界处存在的自滤现象。模拟结果与有关的模型试验结果吻合较好,一定程度上验证了该数值方法的可行性和合理性。本文所揭示的结果有益于对砂土管涌和滤层防治机理的更深入研究。     

砂土管涌－滤层防治的离散元数值模拟

结合小比尺细观模型试验，利用并开发基于离散元理论的颗粒流程序（PFC3D），充分考虑流固耦合作用，建立渗流理论模型，对不同层间系数比下砂土管涌的基料-滤层系统进行离散元数值模拟，跟踪记录渗流过程中砂样运动、流失量、孔隙率、渗透系数、颗粒间接触力、水力梯度等参数的动态变化过程，从细观角度揭示管涌发展过程中颗粒的运动特性和滤层防治机理。数值模拟结果表明，层间系数D15/d85s大小是滤层是否有效的关键因素；在有效的层间系数下，随着水力梯度的加大，基料的细颗粒运动并进入滤层，在滤层－基料交界处存在的自滤现象。模拟结果与有关的模型试验结果吻合甚好，一定程度上验证了该数值方法的和可行性和合理性。本文所揭示的结果有益于对砂土管涌和滤层防治机理的更深入研究。     

地下集水工程渗滤系统的离散元数值模拟

为从细观角度揭示渗滤系统的渗滤机理,利用颗粒流程序建立了充分考虑流固耦合效应的基土-滤层渗滤模型,对其进行不同层间系数下的系列数值模拟试验,并对渗流过程中基土、滤层及两者界面处的孔隙率、渗透率,基土流失量等参数随渗流作用时间的演化过程进行了监测。结果显示:层间系数的取值决定着滤层是否有效及渗滤系统水力特性的优劣;对于地下集水工程中的滤层设计,应能兼顾保土性与透水性的平衡,若其含水层为均匀基土,层间系数D15/d85不宜大于5;数值模拟试验结果与太沙基准则一致,说明采用颗粒流的方法对渗滤系统进行模拟研究是可靠的,因此可用其做更深一步的研究。更多还原     

细沙河道上修建地下集水廊道的工程实践

为弄清地下集水技术在含细沙河流上的适用性及面临的工程问题,以修建在某细沙河道上的两个地下集水廊道工程为例,从含水层颗粒级配入手,探讨滤层设计、出口渗流控制及运行管理等因素对地下集水廊道滤层工作性能的影响,分析了工程滤料失效的原因,提出了相应的改进措施.研究结果表明:在具有一定细沙含量的河道上修建地下集水工程是可行的;当前的滤层设计准则不符合地下集水廊道滤层的运行工况,应重新建立基于低水头、大流量、强透水工况下的滤层设计准则.     

砂砾料反滤设计述评

土石坝的坝体分区和覆盖层的可利用设计中,往往要求反滤层、过渡层和排水体等均要遵循“滤土”和“排水”的准则。事实上,这些分区的反滤设计离不开被保护料、保护料的材料特性,同时与渗流及渗流控制措施密切相关。借相关工程的反滤设计实践,在前人工作的基础上,系统地就反滤层的作用和型式、滤层准则及应用注意事项做些探讨和归纳,以供同行借鉴。     

围井反滤在江西省圩堤堤基管涌抢险中的应用及若干认识

围井反滤技术是针对堤基管涌险情抢护的一种常用且被证明有效的方法.总结了围井反滤滤层保土排水的作用机理,在滤层交界面处形成的自滤层是阻止颗粒流失、保留渗水通道的关键.滤层须满足层间系数要求,且有足够的厚度,这是自滤层形成的必要条件.分析了该技术结构特征及研究现状,认为应根据圩堤典型险情特点对围井结构进行有针对性的设计;宽...     

两种典型级配基土-滤层渗滤系统的颗粒流模拟

基于颗粒流理论和流固耦合效应,利用PFC^3D程序内置的FISH语言编程,建立基土-滤层渗流模型,针对具有不同级配特征的管涌型土(连续级配、间断级配),分别进行不同层间系数情况下的系列数值模拟试验,分析渗滤系统中基土、滤层及两者界面处的孔隙率、渗透率、基土流失百分量等参数随渗流作用时间的演化过程,并分析和评估渗滤系统的保土性和透水性。结果显示对应于不同级配特征的管涌土,其基土-滤层渗滤系统的层间系数值(D₁₅/d_85*)都存在一个最优范围,当层间系数值在该范围内时,由基土-滤层构成的渗滤系统沿渗流方向的透水性逐渐增大,表现出良好的保土性与透水性;连续级配特征的基土自反滤能力较强,其最优层间系数值的范围较宽,而间断级配特征的基土最优层间系数值的范围较窄。     

压密变形对滤层功能的影响

本文在重视土工织物较为松软这一固有特性的基础，进行了试验研究。提出了土工织物滤层和被保护土受压后皆发生不同程度的压密变形，透水性减小．但因材料性质、密度、压力大小的不同，各自渗透系数的减小量不同，对滤层排水功能的影响不同；压密变形，对防止被保护土颗粒流失的滤层功能是有利的。建议应用中应结合工程情况、材料性质、压力大小下测定反映实际的参数，进行滤层设计和选型，以达确保滤层功能和工程安全运行。     

无纺布做堤坝滤层时注意的问题

无纺布在黑龙江省垦区水利工程中普及应用较快,但还是初级阶段。根据初步实践,现就无纺布在堤坝坝滤层设计和施工中的两个问题,谈一下粗浅看法。一、在设计中应认真选型无纺布作为滤层,对无纺布效能的要求,无疑和对砂砾料作垫层的要求是相同的,即能防止管涌(对非粘性土的堤坝尤其如此),又有足够的透水性;其次为耐久性,(抗腐蚀、冰冻和机械磨损等)。对于砂砾滤层,一般是由几层不同粒径的非粘性土(砂、砾或卵石、块石)构成,铺设的方向大体与渗流方向正交,且滤料颗粒随渗流方向而增大,至于每层厚度和     

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。     

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.     

浅谈天湖水电站水轮机运行故障及处理措施

简述天湖水电站投运以来各种故障的表现形式，分析其原因，提出了相应的处理方法及措施，并对合理利用国内外设备提出建议。