侧限条件下原状黄土增湿特性研究

目前,对侧限条件下原状黄土增湿过程中的变形和持水特性研究还较少。以新疆伊犁原状黄土为对象,采用固结仪开展了不同竖向压力作用下的分级增湿试验和湿陷试验。在分级增湿试验中,研究了增湿过程中持水特性以及静止土压力系数的变化规律,提出了侧限条件下土水特征曲线模型以及静止土压力系数的表达式;引入"增湿水平"这一变量描述土体的含水状态,研究了增湿变形与增湿水平的相关关系。最后通过比较增湿试验(单线法)和湿陷试验(双线法)所得到的增湿水平与增湿变形系数关系曲线,验证了两种试验方法在黄土增湿变形研究中的等效性。     

Q3原状黄土与重塑黄土的土水特性研究

黄土土水特征曲线与其强度、渗流及本构关系等密切相关。为研究Q3黄土的土水特性,分别进行了Q3原状黄土和重塑黄土的土水特征曲线测试,并用经典的B-C模型和V-G模型对试验结果进行拟合,分析孔隙比对Q3重塑黄土土水特性的影响。结果表明:原状黄土土水特征曲线分为快速减小、缓慢减小和稳定3个阶段,进气值为20kPa左右,随土体排水,空气进入孔隙内部,吸力逐渐增大,稳定阶段土体饱和度很低,土体处于大吸力段,孔隙排水不明显;重塑黄土土水特征曲线整体趋势与原状黄土一致,但孔隙比对其影响较明显,当孔隙比较大时,体积含水率降低引起吸力明显增加,进气值较小,孔隙比较小时,随着吸力值增加,体积含水率降低速率较小,随着孔隙比减小,土体进气吸力值逐渐增大;采用B-C模型和V-G模型与原状黄土试验结果进行对比,B-C模型低吸力段拟合效果不佳,高吸力段拟合较好,V-G模型整体拟合效果良好。     

湿压条件下黄土结构屈服特性试验研究

湿陷性黄土具有很强的结构性,在增湿及侧限压缩应力作用下,其变形特性表现出与一般黏性土不同的特性,针对这一问题,通过3种不同初始结构性黄土的侧限压缩试验,研究了在增湿及压缩应力条件下黄土的宏观力学特性及其结构变化特征。研究结果表明:在增湿及侧限压缩应力作用下,黄土的应力应变曲线分成3段,即平缓状态段、非线性段和线性段;原状黄土与重塑土压缩曲线的变化,显示出同一压力下黄土架空排列结构破损后孔隙比的可能变化量;原状黄土与饱和黄土压缩曲线的变化,显示出同一压力下黄土颗粒间胶结丧失后结构性黄土孔隙比的可能变化量;结构屈服应力与初始含水率之间满足幂函数关系,压缩指数与初始含水率之满足指数函数关系。     

湿陷性黄土与膨胀土的分级增湿变形特性试验研究

对陕西张桥的湿陷性黄土和安康的膨胀土分别进行了分级增湿变形试验。根据试验结果分析了这两种土的应力应变关系曲线、增湿变形过程中基质吸力变化特点及增湿变形类型。分析表明，其两者的增湿变形应力应变曲线形态完全不同，湿陷性黄土的应力应变曲线明显分为压缩、湿陷变形和固结压密3段，并且在湿陷变形转变为固结压密时有一个明显的转点。膨胀土的应力则随变形增加呈衰减趋势，并且在增湿变形中以体积变形为主，剪切变形较少。湿陷性黄土和膨胀土在增湿过程中基质吸力变化亦表现出明显的差异，前者随含水率明显变化，随应力变化较小，而后者随含水率和应力的增加均有较大变化。最后提出湿陷性黄土的湿陷起始应力和膨胀土的膨胀应力两个概念，进一步合理分析了两者的特征力。     

非饱和黄土宏细观含水状态与结构性的研究

土水特征曲线可以反映土中孔隙的空间分布与变化情况,利用土体的孔隙分布特征可以研究 非饱和土的持水特性和结构特性。首先通过室内压力膜仪试验,研究了非饱和黄土的土水特征曲线的 进气压力值、脱湿速率、孔径分布参数等指标与干密度、击实含水率的关系;然后基于孔径分布计算理论 和试验结果,给出了非饱和黄土的孔径分布曲线,用来评价土体内部孔径的分布情况,分析了非饱和黄 土干密度和击实含水率对土的宏细观含水状态和结构性的影响机理。结果表明:增大非饱和土的干密 度,可使孔径变小,孔隙结构分布范围变窄,土颗粒从架状结构向致密结构转换,基质吸力变化引起含水 率变化较小,持水特性提高,土体的脱湿速率变慢,进气值呈现增大趋势;而击实含水率位于最优含水率 湿测时,影响并不明显。     

原状黄土增湿变形起始屈服函数研究

为研究黄土的增湿变形问题,通过常规三轴剪切试验、等向压缩试验,分别研究了不同初始含水率原状黄土试样的应力-应变关系。通过三轴剪切试验发现,原状黄土的临界状态线近似一条直线且不通过p-q平面的坐标原点,随初始含水率变化沿q轴上下平移。通过三轴压缩试验发现,原状黄土的e-lnp曲线不是一条直线而是折线,且折点处对应的球应力随初始含水率的增大而减小。采用椭圆形屈服轨迹的假设,结合试验规律得出原状黄土试样的起始屈服函数,通过该起始屈服函数可以得出各应力路径下的起始屈服应力和起始含水率。该研究成果是后续建立原状黄土增湿变形本构模型的基础。     

竖向压力作用下重塑黄土土柱压缩湿陷及渗水试验研究

为了探讨竖向压力对兰州非饱和重塑黄土土柱压缩湿陷特性、入渗过程及土-水特征的影响,利用一维土柱渗透仪开展了不同竖向压力作用下非饱和重塑黄土土柱的常水头渗水试验,得到其压缩湿陷曲线,浸润峰、入渗量、体积含水量时程曲线与监测截面土-水特征曲线。研究结果表明:(1)土柱压缩性与湿陷性在试验压力下与常规试验皆有差异;尺寸效应不影响试验黄土结构强度,对其湿陷起始压力影响不大;(2)土柱增湿时浸润峰的前行速率随竖向压力的增大而逐渐减小;增湿过程中土柱在力与水作用下入渗能力变化导致入渗速率曲线有交叉现象,且竖向压力越大入渗速率变化范围越小;(3)竖向压力作用改变了渗水路径,从而影响了监测点体积含水率的变化;(4)竖向压力作用对土-水特征曲线的三个阶段均有影响,压力作用时土柱饱和度皆大于无压力作用,且随着压力增大饱和度逐步增大,当吸力趋于0时,土样未完全饱和。最后利用经典Van Genuchten模型对不同竖向压力下土-水特征曲线进行拟合,模型拟合效果较好。通过试验及分析,为兰州新区建设提供相关参考依据。     

延安新区黄土结构性参数对无侧限抗压强度的影响规律

为研究高填方黄土的结构性在无侧限压缩状态下对其强度与变形特性的影响,以延安新区某高填方场地黄土为研究对象,开展不同试验条件下原状黄土与重塑黄土无侧限抗压强度试验,研究含水率与压实度对黄土结构性的变化规律及其力学特性的影响,并构建原状黄土和重塑黄土的初始结构参数与抗压强度关系的数学模型。结果表明：随着土样含水率的增大或压实度的减小,土体的应力-应变关系曲线由“陡峭”向“平缓”特征过渡,应力峰值减小且后移,结构性参数-应变关系曲线的峰值减小且前移;塑性指标可以作为影响初始结构性参数变化的临界值指标,含水率小于塑限值时,小应变会导致黄土结构性增强,反之则减弱;随着含水率的增大,初始结构性参数呈非线性减小,抗压强度呈线性减小;原状黄土结构性参数-应变关系曲线比相应的重塑黄土曲线分布“陡峭”,含水率增大对原状黄土初始结构性的削弱程度明显大于重塑黄土;初始结构性参数与抗压强度具有非线性关系,可较为精确地表征出原状黄土和重塑黄土基于抗压强度、饱和黄土抗压强度及初始结构性参数的双曲线函数模型。     

考虑体积变化的非饱和膨胀土土水特征

为探讨吸力作用下膨胀土体变特征对土水特征的影响规律,开展了一系列完整的脱湿阶段试验,获得了5种不同初始孔隙比的荆门压实膨胀土各级吸力下的重力含水率与体积变化。试验结果表明：不同初始孔隙比下的重力含水率一吸力曲线有交叉与聚拢现象;体积含水率一吸力曲线的交叉现象更为显著;而饱和度一吸力曲线未出现交叉,相同吸力下初始孔隙比大的土样具有更低的饱和度,体现出土水特征与体变特征的耦合效应。基于试验成果,从土的基本体积一质量关系出发,以初始孔隙比与吸力为变量,在一个统一的框架内,构建了吸力作用下的体变方程、分别用重力含水率与饱和度表征的土水特征曲线方程,该方程能够描述任意初始孔隙比条件下膨胀土干缩过程中重力含水率、孔隙比与饱和度随吸力的变化规律。     

考虑体积变化的非饱和膨胀土土水特征

为探讨吸力作用下膨胀土体变特征对土水特征的影响规律,开展了一系列完整的脱湿阶段试验,获得了5种不同初始孔隙比的荆门压实膨胀土各级吸力下的重力含水率与体积变化。试验结果表明：不同初始孔隙比下的重力含水率－吸力曲线有交叉与聚拢现象;体积含水率－吸力曲线的交叉现象更为显著;而饱和度－吸力曲线未出现交叉,相同吸力下初始孔隙比大的土样具有更低的饱和度,体现出土水特征与体变特征的耦合效应。基于试验成果,从土的基本体积－质量关系出发,以初始孔隙比与吸力为变量,在一个统一的框架内,构建了吸力作用下的体变方程、分别用重力含水率与饱和度表征的SWCC方程,方程能够描述任意初始孔隙比条件下膨胀土干缩过程中重力含水率、孔隙比与饱和度随吸力的变化规律。     

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.