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均匀湿颗粒材料边界滞回持水曲线的物理模型 总被引:1,自引:0,他引:1
非饱和土持水特性的滞回机理是土力学界的热点问题之一。将非饱和土看作“湿颗粒材料”并以“颗粒—系统”为视角更易认识其持水特性的滞回机理。以均匀湿颗粒材料为研究对象,用轴对称圆锥形孔隙内水分的充填和排出过程来模拟边界增、减湿过程,提出一种物理模型以描述其滞回特性的物理内涵,并利用已有文献中3种砂土和2种含黏砂土的持水试验结果验证了该模型在表征均匀湿颗粒材料边界滞回持水曲线时的有效性。该模型的优点在于不仅对同种均匀湿颗粒材料滞回的边界减、增湿持水曲线可采用同一组具有物理意义的参数模拟,而且可反映孔隙水内封闭气泡对持水曲线的影响。 相似文献
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为了研究粒度对非饱和土土-水特性的影响,利用GCTS土-水特征曲线仪对三种不同粒度的西安黄土、青藏黏土、新疆黄土分别进行了增减湿循环试验,采用Gardner模型拟合得到三种土的土水特征滞回曲线,根据滞回度的概念,定量的衡量土的滞回水平的强弱,进一步研究了固体颗粒的粒度对非饱和土土水特征曲线滞回特性的影响。结果表明:有效粒径越大,土水特征曲线的滞回度越大(滞回水平越强),不均匀系数越大,土水特征曲线的滞回度越小(滞回水平越弱)。究其原因是土颗粒之间孔隙尺寸大小对增减湿瓶颈效应和接触角效应的影响。 相似文献
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以van Genuchten模型为基础,将砂土的基本物理特征与统计分析相结合,构建土壤转换函数以预测砂土持水曲线。首先,在土壤转换函数中引入控制粒径d60和不均匀系数Cu这两个典型颗粒级配参数,并满足完全均匀和完全分散的两种理想颗粒材料条件;其次,结合非饱和土水力特性数据库(UNSODA)与4种颗粒级配分布较均匀的砂土持水曲线补充试验,通过量纲分析和回归分析,将控制持水曲线进气值和减湿率的参数a和n分别表示为d60和lgCu的反比例型转换函数,结果表明:这两种转换函数对参数a和n的预测效果优于已有转换函数;最后,将这两种转换函数引入非饱和强度公式,利用已有文献中的非饱和强度试验结果验证了提出的土壤转换函数在表征砂土毛细黏聚力与抗拉强度随基质吸力变化规律的有效性,相应的理论计算结果表明:砂土的毛细黏聚力随其控制粒径减小或均匀程度降低而增高。 相似文献
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考虑残余含气量的毛细滞回内变量模型必须给定三条边界土水特征曲线,即初始脱湿曲线(IDC)、主脱湿曲线(MDC)、主吸湿曲线(MWC)才能对非饱和土的高阶扫描线进行计算。而土水特征曲线的测定需要花费较长时间,费时费力。基于非饱和介质微观理论,研究了孔隙介质的吸/脱湿现象及毛细滞回现象,结合已有经验模型,提出不需要任何参数的经验模型来计算主脱湿曲线。若根据试验数据已知初始脱湿曲线、主吸湿曲线,则该模型不需要任何参数便可直接计算得出主脱湿曲线。最后通过试验数据对模型进行验证,结果表明所提出的模型预测效果较好。 相似文献
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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。 相似文献
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针对现实中土体含水量任意变化的情况,采用滤纸法测定非饱和膨胀土任意循环路径下对应的总吸力和基质吸力,得到了任意含水率变化下的总吸力曲线和土水特征曲线。将曲线进行拟合,利用毛细滞回内变量模型进行计算,通过与试验结果对比,验证了该模型对于膨胀土的适用性。结果表明:滤纸法测得的土水特征曲线与传统方法测得的曲线大致相同。含水量任意变化下的曲线不与完整脱、吸湿曲线重合,相同含水率下,脱、吸湿开始点之间含水率差值越小,脱湿后吸湿的曲线,基质吸力越高;吸湿后脱湿的曲线,基质吸力越低。毛细滞回内变量模型适用于非饱和膨胀土,计算结果与实际值能较好吻合。 相似文献
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非饱和高液限土土-水特性试验研究 总被引:1,自引:0,他引:1
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。 相似文献
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从土颗粒的微观尺度认识和解释非饱和土的基本性质已成为土力学界日益关注的课题之一,将非饱和土作为湿颗粒材料来研究湿颗粒与液桥的相互作用更易认识其内在的微观水力特性。为研究一对不等径湿颗粒间形成液桥时表现的微观水力特性,用相应的光滑球体颗粒的间距描述颗粒表面的粗糙度,假定液桥的形状为圆环且不考虑颗粒重力和浮力的影响,提出了表征这对湿颗粒与液桥相互作用的理论模型。随后研究了液桥体积和毛细作用力与基质吸力、颗粒半径比、固-液接触角、颗粒表面粗糙度的无量纲关系,而且分析了干燥条件下颗粒间液体和液体蒸汽间的平衡关系。最后利用已有文献对球体颗粒间液桥的毛细作用力实测值验证了该模型在表征液桥毛细作用力与颗粒间距关系时的有效性。 相似文献
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循环荷载作用下,砂土的应力应变关系会出现非线性、滞回性的性质,且砂土的变形会出现加载剪胀、卸载剪缩的性质。采用颗粒流软件模拟砂土在循环剪切条件下的变形特性,包括循环应力比、应力水平对变形特性,阐明砂土宏观力学特性及细观工作机理,为建立更为合理的土体本构模型提供参考,并对不良砂土地基防治具有一定的指导。 相似文献
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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。 相似文献
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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. 相似文献
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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. 相似文献
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V. K. Konovalov O. V. Yashkin V. V. Ermakov 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2008,42(2):105-109
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.
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Translated from élektricheskie Stantsii, No. 2, pp. 26–30 (2008). 相似文献
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Peter B. Bayley 《河流研究与利用》1991,6(2):75-86
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. 相似文献
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简述天湖水电站投运以来各种故障的表现形式,分析其原因,提出了相应的处理方法及措施,并对合理利用国内外设备提出建议。 相似文献