循环荷载作用下土工格栅剪切特性的颗粒流细观分析

以循环荷载作用下土工格栅与砂土的直剪室内试验结果为基础,对法向循环荷载作用下筋土直剪过程进行三维颗粒流模拟,开发CLUMP颗粒板替代顶墙施加法向循环荷载。与静载作用室内试验结果相对比,数值试验可以从宏细观角度分析土工格栅在直剪试验中筋土作用特性。研究结果表明:离散元PFC数值试验可以较好地再现筋土界面作用特性。相比静载作用情况,法向循环荷载使得试样上部区域和筋土界面区域颗粒位移明显增加,循环荷载峰值谷值交替出现,筋土界面区域孔隙率呈现波动变化,颗粒旋转明显,滑动比较大。随着土工格栅埋深的增加,法向循环荷载影响逐渐减弱,筋土界面剪应力峰值上升,循环荷载弱化了土工格栅的加筋作用。循环荷载作用下土工格栅与土颗粒的咬合力以及颗粒间的静摩擦阻力、滑动摩擦阻力与滚动摩擦阻力是形成土工格栅加筋作用的主要原因。     

土工格栅筋土界面摩阻力分布拉拔试验研究

通过土工格栅拉拔试验对筋土界面摩阻力横向分布进行了研究,通过千分表测试土工格栅不同位置处的位移,将位移转换成土工格栅应变,根据格栅的抗拉弹性模量得到土工格栅不同位置处的筋土界面摩阻力。试验结果表明:筋土界面摩阻力的峰值出现在土工格栅的横肋处,并沿横肋向两侧逐渐减小;对于单向土工格栅,格栅横肋不仅能够提供筋土界面摩阻力,而且能通过嵌锁作用限制土体的变形,能显著提升土工格栅的加筋效果;土工格栅前半段的筋土界面摩阻力先得到发挥,然后后半段的筋土界面摩阻力逐渐得到发挥。     

不同角度土工格栅加筋剪切特性的试验研究

研究土工合成材料与砂土之间的界面剪切特性的试验通常将土工合成材料水平放置在上下盒之间,但是在加筋体结构中,加筋土的潜在破坏面常常与加筋材料呈一定角度,因此探究加筋材料与剪切面成一定角度时的剪切界面特性有着十分重要的意义。为了探究土工格栅加筋角度对抗剪强度的影响,采用HM-5780大型直剪仪开展了一系列的土工格栅多角度加筋的直剪试验,对比了不加筋状态下的剪切特性,并结合了剪后土工格栅变形特点进行分析。试验表明,在60°加筋时,抗剪强度最大,筋材在剪切过程中主要呈受拉状态,120°和150°加筋时反而削弱了土体的抗剪强度,筋材主要呈受压状态。筋材布置角度越接近剪切过程中最大拉伸应变的方向,则其抗剪强度增加得越多。     

土工格栅与饱和细砂的界面特性试验研究

筋土界面特性是加筋土结构设计的重要技术指标,是揭示土工合成材料加筋机理的关键。采用GDS界面剪切仪研究了剪切速率、竖向应力及网孔尺寸对土工格栅与饱和细砂界面特性的影响。试验结果表明:剪切速率较小(≤1.0 mm/min)时,剪切速率对界面抗剪强度影响不大;剪切速率在1.0~10 mm/min范围内,随着剪切速率的增大,界面抗剪强度先增大后减小;界面抗剪强度随着竖向应力的增加而增大,竖向应力增强了土工格栅对土颗粒的嵌锁作用,限制了土颗粒的剪切移动,从而提高了土体的抗剪强度;剪切速率为1.0 mm/min,竖向应力较小(50~100 kPa)时,小网孔尺寸土工格栅加筋效果更明显;剪切速率为0.1 mm/min,竖向应力较大(200~300 kPa)时,大网孔尺寸土工格栅加筋效果更明显。研究结果对土工格栅在加筋土中的应用具有参考价值。     

第八届中国土工合成材料会议论文：带加强节点双向土工格栅的拉拔试验研究

在传统双向土工格栅的节点上设置一定厚度的加强节点，以形成具备立体加筋效果的带加强节点土工格栅。通过一系列的室内拉拔试验，研究了带加强节点土工格栅筋–土界面作用特性，探讨了横肋间距和加强节点厚度对极限拉拔阻力的影响。结果表明，拉拔曲线在法向应力较小时出现峰值，法向应力较大时表现出应变硬化的特征。带加强节点土工格栅的极限拉拔阻力较传统土工格栅都有一定程度的提高，且随着横肋间距的增大而减小，随着加强节点厚度的增加而线性增大。基于试验结果分析极限拉拔阻力的组成发现，随着横肋间距的增大，极限拉拔阻力的主导作用力由横肋极限端承阻力转变为筋–土界面间的极限摩阻力。     

带加强节点双向土工格栅的拉拔试验研究

在传统双向土工格栅的节点上设置一定厚度的加强节点,以形成具有立体加筋效果的带加强节点土工格栅。通过室内拉拔试验,研究了带加强节点土工格栅筋-土界面作用特性,探讨了横肋间距和加强节点厚度对极限拉拔阻力的影响。结果表明,拉拔曲线在法向应力较小时出现峰值,法向应力较大时表现出应变硬化的特征。带加强节点土工格栅的极限拉拔阻力较传统土工格栅都有一定程度的提高,且随着横肋间距的增大而减小,随着加强节点厚度的增加而线性增大。基于试验结果分析极限拉拔阻力的组成发现,随着横肋间距的增大,极限拉拔阻力的主导作用力由横肋极限端承阻力转变为筋-土界面间的极限摩阻力。     

吸湿条件下土工格栅加筋膨胀土边坡稳定分析

正在设计中的中国南水北调中线工程有约340km的渠段通过膨胀土(岩)地区,拟采用土工格栅加筋膨胀土开挖料处理膨胀土(岩)渠坡.为研究吸湿条件下土工格栅加筋的效果,基于土工格栅与压实膨胀土间相互作用的试验结果.以及提出的膨胀土吸湿变形的模拟方法,对土工格栅加筋膨胀土边坡的应力与变形进行了数值分析.采用Mohr-Coulomb模型模拟膨胀土,线弹性模型模拟土工格栅;并采用理想弹塑性模型模拟土工格栅与压实膨胀土间的界面.研究了土工格栅与膨胀土的界面和压实膨胀土的强度参数,以及土工格栅的弹性模量等因素对加筋效果的影响.研究结果表明:土工格栅与压实膨胀土间界面的强度参数对加筋效果的影响较大;而采用相同的加筋参数,填土的强度参数对坡体的水平变形影响不大;土工格栅的弹性模量越大,对边坡变形的约束作用越明显.     

级配对堆石-土工格栅界面剪切特性影响试验研究

为研究堆石级配对堆石-土工格栅界面剪切特性的影响,根据Einav提出的堆石级配方程配制5种不同级配的堆石试样,进行了设土工格栅加筋与不设土工格栅加筋堆石的界面直剪试验,分析了最大粒径和分形维数对界面抗剪强度以及加筋系数的影响,并给出了加筋系数与堆石平均粒径d₅₀与土工格栅网孔尺寸之比（粒孔比）的关系。试验结果表明,土工格栅的加筋作用主要取决于堆石颗粒与格栅之间的嵌锁作用。当堆石材料中小于格栅网孔尺寸的粗粒含量较高时,嵌锁作用显著,界面抗剪强度增大。反之,当堆石中大于格栅网孔尺寸的粗粒含量较高时,堆石与格栅间的嵌锁作用减弱,滑动作用增强,界面抗剪强度降低。因此,加筋系数随堆石级配最大粒径的增大而减小,随分形维数的增大而增大。此外,加筋系数随粒孔比的增大呈指数衰减,当粒孔比小于0.22时,加筋系数大于1.0,粒孔比大于0.3后,加筋系数趋于0.8。该试验结果对坝顶土工格栅加筋体结构的设计具有重要的参考价值。     

土工格栅与砂垫层界面力学特性试验研究

筋土间相互作用是加筋土强度提高的根本原因,是土工合成材料加筋加固应用中的核心问题。通过室内拉拔试验,分析了法向应力、砂垫层厚度、土工格栅横肋间距3个因素对加筋体极限拉拔力的影响,从宏观角度揭示了筋土界面间的力学特性。结果表明:增设5 cm厚的砂垫层后,格栅的极限拉拔力得到显著提高;高法向应力下,砂垫层厚度对拉拔试验结果影响更显著;在土工格栅加筋软土体中,增大横肋间距会减小筋土界面摩擦角,但是对黏聚力影响不大;格栅网格形态是筋土界面特性的重要影响因素。     

基于颗粒流程序的加筋尾矿剪切应变带宏细观分析

为研究土工格栅加筋尾矿坝剪切带影响范围,提升尾矿坝整体稳定性,通过对不同含水率和上覆荷载的尾矿砂进行室内直剪试验,从宏细观2种不同角度分析剪切应变带的影响规律.试验结果表明:试验曲线近似呈线性增长,峰值位移出现在20～25 mm之间,上覆荷载与峰值剪切位移呈正比例关系,增长速度逐渐减缓;尾矿砂含水率为3％、7％、11％...     

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。     

Call for Papers

正As the eldest and most distributed professional journal of water industry,Water Wastewater Engineering(W WE)gained very wide acceptance from the colleagues working in this field in this country since start publication in 1964.Now it is administrated by the Ministry of Construction of the People’s Republic of China and sponsored by the China Civil Engineering Society etc.     

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。     

SPATIAL AND TEMPORAL WATER QUALITY VARIABILITY IN AQUATIC HABITATS OF A CULTIVATED FLOODPLAIN

The floodplains of lowland rivers contain diverse aquatic habitats that provide valuable ecosystem services but are perturbed when intensively cultivated. Hydrologic, water chemistry and biological (fish) conditions in five aquatic habitats along the Coldwater River, Mississippi, were measured for more than 4 years: the river, two severed meanders that functioned as backwaters, a managed wetland and an ephemeral channel draining cultivated fields. Off‐channel habitats were connected to downstream regions 0.10% to 32% of the dry season and 24% to 67% of the wet season. The median temperatures for the five monitored sites ranged from 18°C to 23°C, the median total solids concentration for all sites was 135 mg L^?1, the median total phosphorus was 0.29 mg L^?1 and the median total nitrogen was 1.56 mg L^?1. Chemical and physical water quality displayed strong seasonal differences between the wet winter/spring and the dry summer/fall periods so that temporal variation consisted of gradual seasonal trends superimposed on strong diurnal variations. All off‐channel habitats exhibited periods of hypoxia and temperatures >30°C during the dry season. Between‐site gradients of water and habitat quality were strongly coupled to water depth and runoff loading. The rehabilitation of one backwater by increasing water depth and diverting agricultural runoff was associated with improved water quality and fish species richness relative to an adjacent untreated backwater. The diversion of polluted runoff and the use of water control structures to maintain greater water depth were observed to be effective management tools, but the former reduces the water supply to habitats that tend to dry up and the latter reduces connectivity. Published in 2011 by John Wiley & Sons, Ltd.     

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.     

Spatio‐temporal variation of gross CO2 and CH4 diffusive emissions from Australian reservoirs and natural aquatic ecosystems,and estimation of net reservoir emissions

Carbon dioxide (CO₂) and methane (CH₄) diffusive emissions were measured during two field surveys in Queensland and Tasmania, Australia, using the floating chamber method. Bubbling and degassing emissions in 2010 were estimated in Koombooloomba Dam reservoir using only inverted funnels and gas concentrations, respectively. A total of 14 reservoirs and 16 rivers and lakes were sampled from 2006 to 2010. Spatial variation was substantial within each water body, as well as between them. The main drivers of diffusive emission variation were physiographic region and climate, with a clear demarcation being observed between diffusive emissions from tropical Queensland and temperate Tasmania, and between the humid West Coast Range (Tasmania) and dry Central Plateau (Tasmania). Higher CO₂ and CH₄ diffusive emissions were observed during the dry season, when long water residence times would promote organic matter degradation. Estimated total gross emissions, including diffusive, bubbling and degassing emissions, for Koombooloomba Dam reservoir were about 1.5 × 10⁶ t CO₂eq km² per year, or 24 × 10⁶ t CO₂eq per year. This corresponds to a plant emission factor of 3.18 kg CO₂eq MWh^?1. Using an estimate of terrestrial emissions derived from literature data for the Tully River catchment area, rough estimated net emissions from the catchment area are about 44 kt CO₂eq per year, or 5.83 kg CO₂eq MWh^?1, which is in the lower range of the studied reservoirs.     

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。