考虑应力引起孔隙比变化的土水特征曲线模型

土水特征曲线在非饱和土力学中扮演着非常重要的角色，它已在岩土工程和环境岩土工程得到广泛应用。利用GCTS土水特征曲线仪，测定了无压和一定固结压力下的非饱和黄土土水特征曲线，引入“水土体积比”对已有文献中Saskatchewan粉土、Indian Head冰碛土和黄土的土水特征曲线数据进行分析，结果发现水土体积比随基质吸力的变化在一定应力所致孔隙比（预先固结和固结所致）和基质吸力范围内可归结为一条曲线。基于此认识，对van Genuchten模型进行改进，提出了一种考虑应力引起孔隙比变化的土水特征曲线模型，并验证了该模型的正确性，为研究非饱和土的力-水耦合本构关系提供了一条新思路。     

非饱和重塑低液限黏土体积变化特性试验研究

采用GDS非饱和土三轴仪,在分别控制试样基质吸力和净平均应力条件下,对重塑非饱和低液限黏土的体积变化和含水率变化特性进行了试验研究.试验结果表明,试样的压缩指数密切地依赖于基质吸力,回弹指数也和基质吸力有一定的相关性,而且试样的收缩系数和土水特征曲线也密切地依赖于净平均应力.在给定的基质吸力条件下,随着净平均应力的增加孔隙比和含水率逐渐降低而饱和度逐渐增加,并在较高基质吸力情况下,试样含水率近似线性地依赖于净平均应力.在给定的净平均应力条件下,随着基质吸力的增加试样发生收缩.当试样基质吸力卸载到0时,试验结果表明在低净平均应力下试样发生膨胀,而在较高净平均应力下试样膨胀后发生坍塌.     

粉质砂土的土-水特征及一维应力变形试验研究

浅层非饱和土的力学特性与其土-水特征密切相关,研究自重应力作用下土体的土-水特征曲线及一维应力变形对于边坡、基坑等工程的稳定性分析具有重要意义。采用应力相关的压力板仪对西南某地区的粉质砂土进行了干燥试验及k₀固结试验。结果表明:在较低的竖向应力状态下,应力大小变化对粉质砂土的土-水特征曲线影响不大;在一定的净竖向应力状态下,粉质砂土的体积应变随吸力的增加呈线性增大;在一定的吸力状态下,粉质砂土的k₀固结变形是非线弹性的,净竖向应力越大,土体的体积应变越大,孔隙比越小。     

膨胀土的土水特性试验研究

膨胀土具有吸水膨胀和脱水收缩的特性,利用非饱和土固结仪对南阳地区膨胀土试样进行了土—水特征试验,并根据试验得到的土—水特征曲线得到:试样的含水率随着基质吸力的增大显著减小;随着轴压的增大,孔隙比减小。当吸力相同时,含水率随孔隙比的减小而增大。     

温度对非饱和土土水特征曲线的影响研究进展

总结了影响非饱和土土水特征曲线的因素,包括固结压力、竖向应力、孔隙比、初始含水量、吸力范围等。分析温度对非饱和土土水特征曲线的影响,从理论模型、影响机理和试验研究3个方面进行深入研究。研究表明：当含水量一定时,随着温度的升高,吸力逐渐降低,相应的土水特征曲线向下移动。最后,在分析目前研究现状的基础上,提出了进一步研究的方向。      

非饱和高液限土土-水特性试验研究

为研究非饱和高液限土土-水特性及其不同条件下土-水特性试验的适用性,分别采用滤纸法、非饱和土固结仪法和现场试验法对公路边坡工程中非饱和高液限土进行测量土-水特征曲线的试验研究。结果表明:滤纸法测得的土-水特征曲线与室内方法存在差距,大部分在室内测得土-水特征曲线的回滞圈内,对曲线进行拟合得到含水率与基质吸力对数呈线性关系;室内非饱和土固结仪法试验得到的土-水特征曲线出现滞回效应,曲线利用VG模型可较好地拟合;现场监测得到的土-水特征曲线(SWCC)与室内试验方法的结果存在差距,但大部分在吸湿曲线和脱湿曲线之间,更接近吸湿曲线,曲线受土体上覆应力影响,上覆应力越大曲线越陡,且基质吸力与含水率成负相关,二者不存在滞后现象,曲线可利用线性函数较好地拟合。     

非饱和膨胀土土水特征曲线试验研究

土水特征曲线指的是非饱和土中,基质吸力与含水量的变化关系曲线。非饱和土的抗剪强度、渗透系数、变形特性都与土水特征曲线有关。通过改装的非饱和固结仪,对非饱和膨胀土土水特征曲线进行测定,并对所获得的土水特征曲线进行拟合分析。分析结果显示：所得的膨胀土土水特征曲线符合一般规律,可以为进一步的非饱和抗剪强度试验提供可靠的参数,为工程实践提供试验依据。     

黄河大堤非饱和土土水特征曲线研究

利用改进的非饱和土三轴仪，对黄河大堤重塑非饱和土进行了试验研究，分析了其渗透特性，并选用Van Genuchten模型拟合了试样的土水特征曲线，对不同围压下的土水特征曲线进行了比较。结果表明：①随非饱和土含水量的增大，基质吸力减小，非饱和土的工程性质向弱性变化；②在高含水量下，基质吸力随含水量变化的变化幅度很小，在低含水量(天然含水量)下，基质吸力随含水量的增大而迅速减小；③对某一类土而言，在低吸力下土的基质吸力主要随含水量而变化，在高吸力下其大小除取决于含水量外还受黏粒含量、矿物成分等因素的影响；④相同体积含水量的土壤的基质吸力随着围压的增大而减小，相同基质吸力的土壤的含水量随围压的增大而增大。同时指出，对于黏性较强、有机质含量较高的黄河大堤非饱和土的土水特征曲线，还需要进一步研究。     

非饱和土的土-水特征曲线的试验研究及应用

利用改进的非饱和土三轴仪,对非饱和土在不同围压条件下的基质吸力与含水量关系的试验研究。并根据试验结果,绘制非饱和土的土-水特征曲线与围压-基质吸力关系曲线。分析曲线规律,拟合基质吸力与体积含水量之间的函数,并通过土水特征曲线计算非饱和土的渗透系数及预测非饱和土的抗剪强度。     

基于微观孔隙通道的饱和/非饱和土渗透系数模型及其应用

从微观角度揭示土体变形对饱和/非饱和渗透系数的影响机理,建立相应的预测方法,对于饱和/非饱和土的渗流分析及水力耦合研究具有重要的科学意义。利用流体力学理论,建立了微观孔隙通道渗透系数与等效孔径的关系,在此基础之上,结合毛细理论建立了饱和/非饱和渗透系数与土-水特征曲线的关系模型,并利用已有试验数据验证了模型的合理性。结合该模型与变形条件下土-水特征曲线预测方法,对变形条件下武汉黏性土饱和/非饱和渗透系数进行预测,结果表明黏性土在压缩变形条件下:饱和渗透系数呈数量级的减小,预测值与实测值均吻合较好;双对数坐标下,非饱和相对渗透系数在进气值之后随基质吸力增加而减小,不同初始孔隙比条件下其斜率近似不变,整体呈现"毛刷型"分布,相同基质吸力条件下,初始孔隙比越小,相对渗透系数越大;非饱和渗透系数,进气值之前近似为饱和渗透系数,进气值之后随基质吸力增大而减小,不同初始孔隙比的变化线近似重合。     

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.