干湿循环作用下植被混凝土结构演化

选取植被混凝土生态基材为研究对象,制备6种初始含水率分别为13%、19%、25%、31%、37%、43%的试样。通过烘干法和叠式饱和法分别模拟脱湿和增湿过程,采用土壤收缩仪测量试样宏观胀缩量,Matlab软件提取试样表面裂隙几何特征,探究干湿循环作用下植被混凝土结构演化规律。结果表明:试样在常温下的干缩过程可分为急剧收缩阶段、平缓收缩阶段和稳定阶段3个阶段;干湿循环过程中,试样收缩量与膨胀量近乎等量;裂隙发育过程主要体现在裂隙宽度、总长度及总面积随循环次数增加而增大;初始含水率过低或过高,均易使植被混凝土发生湿胀干缩破坏;初始含水率31%试样的裂隙平均宽度、裂隙总面积、裂隙长度和表面收缩率均最小,31%为生产实践的最佳含水率。     

湿陷性黄土力学性质与裂隙发展干湿循环效应

黄河中游地区广泛存在湿陷性黄土,对黄土试样进行干湿循环处理后,开展土工三轴剪切试验,同时记录样品表面裂缝的拓展特点,探究干湿循环对黄土强度与裂隙发展规律的影响。试验结果表明:黄土样品的应力应变关系均为"硬化型",有效内摩擦角与黏聚力指标随循环次数增加分别呈指数型和线性下降趋势;提取裂隙率作为表面裂隙的量化指标,黄土的裂隙率与循环次数之间为指数型关系;干湿循环作用使得黄土颗粒间的微裂隙逐渐扩张,干密度显著减小,这是导致表面裂隙改变和力学性能衰减的本质原因。     

非贯通裂隙软岩单轴压缩强度特征及贯通机制研究

为了解非贯通裂隙软岩单轴压缩强度特征及其贯通机制,以非贯通裂隙软岩试样为研究对象,进行单轴压缩破坏试验,得到不同裂隙排数、倾角及贯通深度条件下非贯通裂隙软岩试样的强度特征,对破坏试样的裂纹和破坏面进行分析,得到非贯通裂隙软岩试样的裂纹类型和贯通机制。不同裂隙特征参数条件下的对比研究成果表明:不同裂隙排数及贯通深度的非贯通裂隙试样均以30°倾角试样强度为最低,这与贯通裂隙试样存在差异。分析不同裂隙排数及贯通深度的非贯通裂隙试样的强度参数,发现30°倾角试样的黏聚力最低,只有完整岩样黏聚力的43.53%;而倾角相同时,不同裂隙排数的试样强度均随裂隙贯通深度的增加而降低。受荷条件下裂隙间的多次贯通使得非贯通裂隙试样呈现出局部渐进破坏特征,扩展裂纹以次生裂纹为主,翼裂纹初期发育后逐渐停止扩展。裂隙排数对试样贯通机制起主导作用,单排裂隙基本以Ⅰ型张拉破坏为主(60°倾角试样除外),而双排裂隙则以Ⅱ型剪切破坏为主。研究成果对解决实际工程中遇到的破裂岩体强度计算问题和破坏机制问题具有参考价值。     

含砂量对黄原胶复合黏性土抗裂和抗冲刷性能的影响

为增强黏性土的抗裂和抗冲刷性能,对掺加不同含量砂土的黄原胶复合黏性土开展了一系列室内蒸发、干缩开裂和抗冲刷试验,通过测算试样含水率和土体抗冲刷系数,结合图形分析软件定量分析了土体表层裂隙的发育情况,以研究复合黏性土体内部水分变化规律及其抗裂和抗冲刷性能。结果表明：随着黏性土中砂土颗粒的掺入,试样的裂隙率、裂隙宽度和受冲刷破坏程度呈现先增大后减小的趋势;当含砂量为30%时,素土及黄原胶复合试样的裂隙率、裂隙宽度和受冲刷破坏程度均为各含砂量下的最大值;当含砂量为50%左右时,对于黄原胶复合黏性土,黄原胶胶体与砂土颗粒形成具有一定强度的稳定结构,其抗冲刷性能得到显著提高。     

原状Q2黄土结构损伤演化的细观试验研究

利用和CT机配套的多功能土工三轴仪，对原状Q2黄土在三轴剪切过程中内部结构的变化进行了动态、定量和无损的量测，得到了软化破坏土样内部结构演化的CT图像和相应的CT数据，从细观上解释了软化破坏过程。试验结果表明，原状Q2黄土内部存在大量孔隙、裂隙、姜石等结构缺陷，初始损伤明显且具有各向异性。原状Q2黄土软化破坏细观变形可大致分为4个阶段，即微压密阶段，损伤开始阶段，损伤快速发展阶段和损伤减缓发展阶段。剪切过程呈现以局部变形为主的细观变形特点，但整体上CT数减小，方差增大。用CT数和方差均可较好的描述原状Q2黄土软化破坏的损伤演化规律，随着含水率和固结围压的增大，CT数和方差变化率越小。     

土工格栅加筋土三轴试验研究

通过时玻璃纤维土工格栅加筋土体的三轴试验研究,分析不同加筋层数、不同围压对试样应力应变关系曲线、抗剪强度的影响.试验结果表明:加筋作用效果随着轴向应变的增大而增强;同一种加筋材料,加筋层数越多.加筋效果越明显;加筋使得试样具有一定的延性,并能显示出很强的后期效应;在低围压的情况下.采用加筋的方法来提高土的强度更为合理、...     

新型高强经编复合土工织物拉伸特性测试方法

对一种由高模低缩涤纶长丝与丙纶短纤无纺土工织物采用经编工艺加工而成的高强经编复合土工织物进行了系列室内拉伸试验,分析了试样宽度、初始长度等因素对材料力学特性指标的影响,同时比较了宽条法和多肋法这2种不同计算方式得到的拉伸强度值的差异,为这种新材料的拉伸试验方法提供基础依据。试验成果表明:尽管复合织物具有类似土工格栅的加筋网格结构,但由于纵横向长丝与基层无纺织物依靠捆绑丝经编结合成整体,其拉伸强度的计算方法宜采用土工织物宽条法,而不能采用格栅肋条法计算。试样宽度越大,复合织物的拉伸强度越高,当试样宽度>100 mm时,强度基本趋于稳定。另外,试样初始长度的变化对拉伸强度影响不明显,长度增加,最大拉力仅略有降低,但延伸率明显减小,定应变5%对应的拉伸强度有较大提高。建议此类复合织物的拉伸试验宜采用200 mm宽条试样,且初始长度至少不低于300 mm。     

干湿循环下膨胀土裂隙发育与导电特性

干湿循环引起膨胀土裂隙开展,进而对土体的土水特性产生重要影响。首先进行了不同干密度、含水率状态下均质无裂隙试样的导电性能试验,认为试样电导率与干密度、含水率呈线性关系,可采用多元线性函数进行拟合。用远距离光学显微镜观测了膨胀土裂隙发生发展过程,利用图像灰度熵评价裂隙形态,试验过程中同时测定了试样的含水率和电导率,获得了干湿循环下土体灰度熵-含水率-电导率的关系。结果表明:随着含水率的降低,灰度熵逐渐增大,电导率逐渐减小;含水率对电导率的贡献逐渐降低,裂隙对电导率的贡献逐渐增大。当失水到一定程度时,裂隙对电导率的贡献几乎不变,此时表明裂隙已开展稳定;浸水过程中,裂隙部分闭合,灰度熵减小,电导率增大。经历多次干湿循环的试样,灰度熵和电导率均有所降低,表明土体结构产生了不可逆的改变。     

压实条件对膨胀土裂隙发育影响的试验研究

裂隙是影响膨胀土力学特性的重要因素之一。以河南南阳地区高速公路路用膨胀土为研究对象,通过制备不同初始含水率和压实度的大尺寸压实膨胀土土样,观察压实膨胀土在脱湿过程中的表面裂隙发育,并拍摄数码图像,然后利用基于MatLab自编程序的改进裂隙图像特征参数提取方法对图像进行定量化分析,获得裂隙的各种特征参数,进而探讨膨胀土表面裂隙发育的相关规律。研究结果表明:压实膨胀土脱湿开裂过程可分为细小裂隙发育、主裂隙发育及裂隙回稳3个阶段;初始含水率越高,膨胀土表面裂隙发育速率越快,发育程度越高,持续时间越长;初始压实度越大,膨胀土表面裂隙率和裂隙总长越小,但宽度较大。上述裂隙发育规律可用表面蒸发和土体内部水分传输机理进行解释。     

土工合成材料与砂土界面摩擦特性分析

三向土工格栅作为一种新型土工材料已广泛应用于工程实践中,但其理论研究相对落后于实践。通过大型直剪仪,研究了不同强度的单向土工格栅、双向土工格栅、三向土工格栅、玻纤土工格栅和土工布与砂土界面在直接剪切时的相互作用特性,对比分析了上述5种土工合成材料在不同法向应力及剪切速率下的摩擦性能。结果表明,三向土工格栅与砂土界面的剪应力随着剪切速率的增加而减小,在同一法向应力下,三向土工格栅的剪切应力值明显大于单向和双向土工格栅。     

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.