红土应力—应变—体变关系的归一性关系

红土作为一种特殊土，归一化性状是否存在是个值得研究的问题。用平均主应力作为归一化应力，对红土在两种不同应力路径下三轴排水试验的应力－应变－体变关系进行归一性分析研究表明，在１００ｋＰａ～４００ｋＰａ的固结压力下，红土的归一化程度较低，不能求得唯一的归一化曲线，固结压力越低，归一性越差；随压力增大，归一性增强。偏应力－剪应变的归一性高于偏应力－体应变的归一性；对偏应力－剪应变关系，σ３＝ｃ应力路径的     

不同应力路径对加筋土应力—应变关系的影响

对加筋土在常规三轴上进行了三种不同应力路径（σ３＝ｃ、ｐ＝ｃ、η＝ｃ）的试验研究。结果表明：不同应力路径对加筋土的应力应变关系及抗剪强度指标－粘聚力ｃ值有较大影响，但是对其抗剪强度指标－内摩擦角ψ值影响不大。     

不同应力路径对垃圾土应力-应变关系的影响

利用GDS多功能三轴仪对K0固结的垃圾土样进行了七条应力路径的三轴试验,探讨了不同应力路径下垃圾土的应力-应变关系,给出了q-εs、p′-εv、p′-εs和q-εv的关系曲线。结果表明:垃圾土偏应力随剪应变几乎呈线性增加,表现出明显的加工硬化特征。同等剪应变的情况下,当Δp为正Δq也为正时,应力比(η=Δq/Δp)较大的应力路径对应的偏应力较小;当Δp为负Δq为正时,应力比较大的应力路径则表现出较高的抗剪强度。偏应力q不仅与剪应变有关同时也与体应变有关,球应力p不仅与体应变有关还与剪应变有关,填埋方式对垃圾体的应力和应变分布有重要影响。更多还原     

膨胀土侧向卸荷试验研究及归一化特性分析

【目的】为探究膨胀性黏土在侧向卸荷应力路径下的应力-应变特性，【方法】以合肥地区典型膨胀土为研究对象，开展了侧向卸荷应力路径三轴试验，分析了卸荷应力路径下合肥膨胀土的破坏形态、应力-应变特征和强度指标，并基于Kondner双曲线模型，获得了膨胀土卸荷模型参数，对其卸荷应力-应变曲线进行了归一化分析，建立了其归一化方程。【结果】结果显示：在侧向卸荷路径下，膨胀土在不同围压下呈现出剪切、鼓胀劈裂和鼓胀3种破坏形态；膨胀土卸荷应力路径下应力—应变曲线呈双曲线型，为典型应变硬化型土；卸荷路径下膨胀土的黏聚力c=68.4 kPa,明显小于常规加载黏聚力c=101.7 kPa。基于Kondner双曲线模型，建立了以幂因子σ^0.466为归一化因子的膨胀土卸荷归一化经验方程，通过试验验证，该归一化经验方程对合肥地区典型膨胀土卸载应力-应变拟合度达到99%以上，【结论】采用该模型预测合肥地区典型膨胀土在卸荷路径下的应力-应变曲线较为理想。研究结果可为合肥地区典型膨胀土的卸荷工程提供理论支持。     

主应力方向偏转条件下粘性土的变形特性

在研究土体应力应变关系时,应力路径的影响因素是主要研究内容之一。在实际工程中,由于在土体上部加荷,土体中不同位置的主应力方向发生偏转,这是应力路径的一个重要特征。本文介绍了用单剪仪和空心圆柱扭剪仪进行的试验研究成果。试验资料表明,不同应力洛德角θ_σ(相应于不同主应力方向偏转角θ_α)其应力应变关系可用双曲线拟合,但不能归一化,即初始切线斜率和极限应力不同。这说明,第三主应力不变量对应力应变关系和剪切强度存有影响。对剪切强度的影响可用应力状态函数ψ(θ_σ)表示。同时证明,对复杂加荷条件,广义剪应变增量方向不仅是f/q的函数,而且也是(f/θ_σ)/q的函数。因此,不论p—q平面,还是π平面,塑性势函数等于屈服函数,流动规律是相适应的。     

单轴循环受拉条件下SP-HFRC力学性能试验研究

通过对21个钢－聚丙烯混杂纤维混凝土（ＳＰ－ＨＦＲＣ）试件进行单轴循环受拉试验，研究ＳＰＨＦＲＣ在循环受拉条件下的力学行为变化规律。重点分析混杂纤维体积掺量及长径比对应力－应变全曲线、累积塑性应变、刚度退化、应力退化的影响。结果表明:混杂纤维具有逐级阻裂作用使得ＳＰＨＦＲＣ试件呈现明显延性破坏特征；应力－应变全曲线卸载点应变与塑性应变呈线性关系；ＳＰ－ＨＦＲＣ刚度退化过程随钢纤维体积掺量和长径比增加而减缓，受聚丙烯纤维体积掺量的影响不明显；纤维对应力退化率的影响不明显。在试验结果和相关文献试验数据的基础上，建立了ＳＰ－ＨＦＲＣ单轴循环受拉应力－应变全曲线方程，可用于结构非线性和滞回性能等的分析。     

干密度对Q2重塑黄土强度与变形特性的影响

为了研究干密度对Ｑ２重塑黄土强度与变形特性的影响，用非饱和土三轴仪做了３组共２７个试验，在试验过程中干密度、吸力及净围压为不变量，得到Ｑ２重塑黄土的强度及变形特性。试验结果表明:不同干密度下试样的偏应力－轴向应变曲线均呈应变硬化型；相同吸力下，试样的净围压越大，偏应力越大；相同净围压下，试样的吸力越大，偏应力越大。随着干密度增大，试样的偏应力显著增大，硬化趋势也逐渐增强；除个别试样外，其余各试样在剪切过程中均处于剪缩状态；在相同的吸力和净围压下，干密度增大，试样的破坏应力（ｐｆ、ｑｆ）、有效黏聚力ｃ、切线变形模量Ｅｉ、极限偏应力（σ１－σ３）ｕｌｔ及参数ｋ均在增大，参数ｎ随着干密度增大而减小。     

不排水条件下饱和砂土的应力比与应变比之间关系的试验研究

通过饱和砂土的固结不排水三轴试验结果，在不同应力平面（强度发挥面及ＳＭＰ面）上，对剪正应力比￣剪正应变增量比及剪正应力比￣剪正应变全量比关系进行了研究，得知：不同面上应力比￣应变增量比具有较强的线性关系，应力比￣应变全量比关系与σ１￣σ３￣ε１关系的型式相关，在硬化型及软化型的峰值点以前仍有线性关系，并得到了密度，周围压力，应力平面对其线性参数影响的一些规律性认识。     

含水率对青海地区原状黄土力学性能的影响

为了研究青海地区原状黄土在不同含水率下的力学特性,利用英国GDS标准应力路径试验系统对原状黄土进行了不排水三轴试验,并且对偏应力-应变关系进行了归一化分析。建立了考虑含水率和围压影响的归一化偏应力-应变关系,通过计算结果和试验结果对比得出归一化的偏应力-应变关系,预测原状黄土的偏应力-应变关系。结果表明:试样偏应力-应变曲线呈应变硬化型。而且,在相同的围压下,试样最大偏应力随着含水率的增加而减小;弹性模量随着围压的增大而增大,随着含水率的增大而减小;黏聚力随着含水率的增加降幅比较大,内摩擦角变化很小。通过拟合黏聚力与内摩擦角随含水率变化曲线得到以含水率为变量的库仑抗剪强度公式,对青海地区实际工程设计以及地基处理具有一定的参考意义。     

玄武岩纤维混凝土应力-应变全曲线试验研究

玄武岩纤维是混凝土良好的增强增韧材料,应力－应变全曲线是混凝土最基本的本构关系,是钢筋混凝土结构分析中重要的物理方程。采用单轴压缩试验,进行了玄武岩纤维混凝土单轴受压应力－应变全曲线研究,开展了不同纤维掺量与矿物掺合料种类对各特征点应力－应变关系及全曲线本构参数的影响规律研究。研究表明,玄武岩纤维可提高混凝土的韧性和破坏后的延性,掺入玄武岩纤维后混凝土应力－应变全曲线峰值点、反弯点与临界剪切点处的应力均有所提高,在纤维掺量为０．１０％时最大,各点对应的应变随玄武岩纤维掺量增加而增大,在纤维掺量为０．１２％时最大;当纤维掺量为０．１２％时,玄武岩纤维混凝土应力－应变全曲线上升段本构参数αａ为１．７６,下降段本构参数αｄ为１．７１;掺入粉煤灰会进一步降低玄武岩纤维混凝土的脆性,而磨细矿渣粉则相反。     

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.