裂隙岩体渗流场与应力场的耦合数值分析

裂隙岩体渗流场与应力场耦合是一个复杂的地质问题.本文基于裂隙-空隙双重连续介质对裂隙岩体渗流场与应力场进行耦合分析,推导建立了数学模型,并将该模型用于实际边坡工程的岩体裂隙进行数值模拟,分别对不考虑应力影响下的渗流场和不考虑渗流影响下的应力场以及两场相互耦合时的稳定性进行了研究,由于耦合作用下与任意单场作用下相比差异较大,因此考虑岩体裂隙多场耦合作用是必要的也是符合事实的[1].     

岩体单裂隙流固热化学耦合作用数值模拟研究

为全面研究渗流、应力、化学、温度影响下岩体裂隙的变化,建立了岩体单裂隙的流-固-热-化四场全耦合数学模型,并以Comsol Multiphysics软件为基础,将该数学模型转化为一个统一的偏微分方程组,实现了四场全耦合数值求解。该模型给出了更接近真实物理过程的数值解答,避免用松散耦合法求解多场耦合问题带来的误差。同时通过对两个实例的计算模拟,分析了在渗流、压应力、水化学溶蚀和温度等多因素耦合作用下,岩体单裂隙渗透特性的变化规律,得出了裂隙岩体渗透特性的影响机理和关键影响因素。     

岩体裂缝扩展的渗流-应力耦合分析模型

应用无单元法,对渗流场和与应力场耦合作用下的岩体裂缝扩展进行追踪。裂缝扩展计算采用断裂力学最大周向正应力理论。应力场和渗流场的耦合作用通过以渗透压力和渗透系数为交互因子的迭代计算考虑,其中裂缝区还考虑了裂缝中水对缝壁的拖曳力。裂缝扩展计算每一步所产生的新结构都要进行渗流-应力耦合分析,直至裂缝稳定为止。算例结果表明,所建数值模型能较真实地反映水流对裂缝扩展的影响,并能较好地模拟渗流-应力耦合作用下的裂缝扩展过程。     

岩体渗流-应力耦合裂隙网络模型研究进展

裂隙岩体结构复杂,岩体的渗流特性与应力环境存在着密切关系,渗流场对应力场同样也存在影响.在国内外相关研究的基础上,系统地归纳了岩体渗流-应力耦合裂隙网络模型的建立思路、裂隙处理方法等.提出地下岩体中裂隙网络是无法完全可观测的,实际得到的数据并不充分,在随机模拟时,如何选择反映实际岩体特性的随机分布还有待进一步研究,在耦合模型中如何更真实地表征裂隙随应力的变化关系也需进一步研究.     

渗流应力作用下层理岩体稳定性数值分析

为研究渗流应力耦合作用下含倾角层理岩体的稳定性,基于岩体极限平衡状态方程,以30°层理白云岩为例,推导该层理岩体在渗流应力耦合作用下的稳定性判别式,通过等效连续介质模型和Louis经验公式,建立渗流应力耦合模型,并采用Midas GTS NX对该层理岩体进行渗流应力耦合作用稳定性分析,建立相应的数值试验。结果表明,所建立的渗流应力耦合模型分别对10和50 kN/m荷载作用下的层理岩体总水头、总位移、剪应变进行数值分析,模型的计算结果与判别式计算结果拟合度较好;判断了层理岩体的稳定性,可为类似研究提供相应的理论依据,具有一定工程应用价值。     

西非高温干旱地区混凝土重力坝仿真研究

通过对重力坝的建模仿真分析是研究其坝体应力分布变化规律的重要方法之一。为了更加准确地模拟大坝在实际工程中的运行情况，使用COMSOL Mul-tiphysics高级数值仿真软件的耦合功能，结合西非高温干旱地区的气候、水文特点，从温度、渗流以及本身所受重力对重力坝进行耦合分析，并就单重力场、温度场与重力场耦合、渗流场与重力场耦合及三场耦合4种情况对重力坝的应力分布进行对比研究，最终得出结论：通过对比4种条件下重力坝应力分布，在考虑高温干旱条件下，温度对重力坝的应力分布影响比渗流的影响较大。综合考虑多场耦合作用，能够为实际工程坝体设计提供更科学的依据，故对重力坝进行多物理场耦合分析具有重要意义。     

小湾电站坝址区渗流与应力场耦合分析

本文研究了小湾电站坝址区岩体渗流场与应力场的耦合相互作用，并结合右坝肩Ｆ１１断层的特性，探讨了裂隙内具有不同填充物情况下，裂隙表面分形对裂隙渗流和应力的影响，通过数值分析，得到了场耦合情况下的渗流分布及断层Ｆ１１在不同应力水平下的分维数－渗流量、不同分维数下的应力－裂隙开度、应力－流量关系曲线。     

小湾高拱坝坝区渗流场对应力场的影响

结合小湾水电站高拱坝工程，分析坝区岩体多重理解隙网络渗流的特点及渗流对应力的影响机理，采用多重裂隙网络模型和有限元数值方法对小湾高拱坝建坝蓄水后坝区渗流场和渗流场影响下的应力场进行分析计算。可以看出，建坝蓄水使坝区渗流场发生较大变化，且使大坝附近的坝基岩体竖向有效应力有增大，也使坝肩岩体的拉应力增大。     

裂隙网络岩体非稳定渗流场与应力场耦合分析

岩体裂隙网络渗流的特点是渗流沿裂隙网络定向流动,体现出明显的非均匀性和各向异性,这决定了裂隙网络渗流的特殊性;裂隙岩体中渗流与应力的相瓦作用主要也是通过岩体中的裂隙.从裂隙网络渗流的特点出发,以岩体裂隙网络渗流与岩体应力相互影响、相互作用的耦合机理为基础,研究裂隙岩体中渗流场和应力场相互影响以及二者随渗透水流时间及边界条件的变化规律\编制相应程序,并通过算例进行了验证;考虑耦合情况下,裂隙岩体渗流场与应力场较不考虑耦合时均有明显变化.     

裂隙岩体渗流新模型

为适应网状和层状渗透结构，根据多边形裂隙网络理论．确立了裂隙网络生成的原理和方法，系统地推导了在渗流和应力耦合作用下裂隙岩体渗流模型。并结合拉西瓦水电站坝区岩体裂隙构造的特征，进行了渗流计算和分析；还与连续介质和裂隙网络渗流模型进行了计算比较。     

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。     

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.     

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。     

Desiccation and recolonization of phytobenthos in a regulated desert river: Colorado River at Lees Ferry,Arizona, USA

We tested the recolonization of the phytobenthic community in the tailwaters of Glen Canyon Dam following long- and short-term experimentally induced desiccation. The response of Cladophora glomerata, Oscillatoria spp., miscellaneous phytobenthos species and periphyton was studied over 18 weeks using three treatments: (1) undisturbed control cobbles from the submerged zone; (2) cobbles desiccated and replaced into the submerged zone; and (3) cobbles desiccated and replaced into the varial zone. Periphyton density and compositional response resulting from these treatments were also examined. Desiccation treatments were significantly different in biomass from controls throughout the study. The biomass of desiccated and replaced river cobbles averaged <30% of the controls for C. glomerata and periphyton during the 18-week recolonization period. In contrast, the biomass of the control Oscillatoria and miscellaneous phytobenthos species averaged only 3 and 50% of that in the desiccation treatments, respectively. Cladophora, the dominant alga, comprised 77% of the phytobenthic biomass. A significant positive relationship between discharge, Cladophora and periphyton biomass was present in all treatments, while there was a negative relationship with discharge for Oscillatoria and miscellaneous phytobenthos species. There was a significant inverse correlation, as well as a pattern of separate biomass dominance, between C. glomerata and Oscillatoria. Cladophora was the dominant phytobenthos species on cobbles below the baseflow and Oscillatoria was dominant on cobbles in the varial zone. In general, the Cladophora biomass decreased under intermittent drying conditions, while Oscillatoria declined under permanently wet conditions. Diatom composition was not significantly different between treatments; however, their density was lower on desiccated cobbles. Diatom density on desiccated cobbles in the submerged and varial zones averaged 69 and 42% of that of the controls, respectively. Recovery and maintenance of benthic resources are hindered by fluctuating flow regimes driven by electricity and irrigation requirements. Repeated desiccation of the phytobenthos has major effects on the bottom-up interactions in the Colorado River ecosystem. © 1998 John Wiley & Sons, Ltd.