基于Voellmy模型的哀牢山地区滑坡泥石流灾害运动过程数值模拟

我国西南山区滑坡泥石流灾害常发,滑坡泥石流灾害体运移堆积的范围是开展区域地质灾害危险性评价的重要指标之一。以云南省哀牢山地区水塘镇芭蕉树滑坡泥石流灾害为研究对象,利用Voellmy流体运动模型进行灾害体运移堆积全过程数值模拟反分析,获取数值模拟模型参数。利用反分析得到的模型参数建立与芭蕉树滑坡泥石流所处地质环境条件相似的戛洒镇南恩小学滑坡数值模型,进行滑坡泥石流灾害运移堆积过程模拟分析,模拟结果与野外地质灾害危险性评估结论符合程度较高。     

泥石流动力过程及沿程侵蚀研究综述

研究泥石流的动力过程可以反演泥石流灾害的发生和发展过程,便于人们认识灾害的形成规律和特征。首先介绍了国内外泥石流动力模型,包括以Bingham模型、Bagnold膨胀流模型和库伦颗粒流模型为主的单流体模型和多流体模型,然后对泥石流动力过程数值模拟进行了梳理与分析,提出数值模拟中需要注意的问题,特别分析了泥石流沿程侵蚀作用在泥石流动力过程研究中的重要作用。最后,提出了泥石流动力过程研究存在的问题及发展方向。以期为泥石流动力过程的深入研究及防灾减灾提供一定的指导与借鉴。     

泥石流动力学模型和数值模拟研究综述

泥石流体可视为介于挟沙水体和土体之间的过渡性体,它兼具水体和土体的性质,有着不同于两者的固有性质.现有的泥石流动力学模型都是从水沙或者岩土力学模型基础上发展而来的,从描述组成物质和运动的观点来看,可划分为连续介质、离散介质和混合介质模型.前两种模型可以在一定程度上描述某些泥石流物理现象.传统的单流体和多流体模型都属于连续介质模型.离散介质模型主要有离散元模型和动理学模型.混合介质模型能完整反映泥石流的物理本质,但面临的理论和计算问题也最多,正处于初步发展阶段.基于不同的动力模型和数值算法,目前发展了种类较多的数值计算模型.单流体的数值计算模型相对比较成熟,应用也比较广泛.具体的数值计算模型中,数值算法、流变模型、地形数据、边界和初始条件等的处理对数值计算结果有重要的影响,需要根据具体的问题选择合适的数值计算模型.泥石流动力学模型和数值模拟研究的重点在于建立全过程的泥石流动力学模型和模拟,发展非均质的泥石流计算模型,客观反映大尺度颗粒和障碍物的存在对泥石流运动的影响,以及建立合理的泥石流动床物质交换模型.     

泥石流细颗粒浆体的有效浓度

粘性泥石流和稀性泥石流中的细颗粒含量基本相同,但它们的浆体浓度和物理力学性质却差异甚大.本文将从泥石流的颗粒组成出发,分析粗颗粒在泥石流中的作用,提出能够反映粗颗粒影响的有效浓度概念,给出一个计算实例,以说明它的计算方法.     

基于动力学与物质条件的泥石流阻塞大河综合判据

受强震与极端天气事件的影响,泥石流阻塞大河事件呈急剧上升趋势,以往的研究多数针对泥石流堵断小河的物理过程,所建立的公式不适用于主河强水流作用下的泥石流阻塞大河问题.本文参考了Takahashi提出的泥石流在坡度变化沟道中的运动方程,考虑泥石流汇入主河后动力过程受主河水流阻力影响的因素,建立了泥石流进入主河后的运移距离计算公式;基于岷江典型河段实测和泥石流堵河水槽模型试验,确定了泥石流物质总量与堵塞系数之间的关系式;大直剪试验表明,当大颗粒体积比达到50%时,粗细混合料的抗剪强度由大颗粒所决定,据此提出堰塞坝形成稳定坝体的条件是抗水流冲刷的大颗粒所占比例达到50%以上,并通过现场资料对这一结论进行了验证.从而建立了基于泥石流在大河中运移距离、泥石流物质总量及泥石流体颗粒组构条件的泥石流阻塞大河综合判据.     

泥石流的固液两相分界粒径

固液两相分界粒径的划分是采用两相流理论研究非均质泥石流的关键问题之一。通过分析泥石流液相浆体的组成机理,以及泥石流野外实测资料和试验数据发现,分界粒径与泥石流的容重、黏度和流速等因素密切相关;根据不同粒径颗粒的物理力学性质和运动特征,以及浆体中所含颗粒主要处于悬浮状态且不发生分选的特点认为,泥石流的分界粒径将随自身的演进过程在某个范围内发生变化,且其最大变化值与泥石流的颗粒组成和运动特征有关。根据各类泥石流中固相和液相的应力特征,分别讨论了不同输沙模式下分界粒径的确定方法。基于非均匀悬移质输沙理论,从泥石流运动过程中粗细颗粒交换的角度出发,利用挟沙力的概念建立了一套适用于两相紊流输沙模式下分界粒径的确定方法,其同时考虑了泥石流容重、黏度及流速等因素的影响,比较切合实际且能与实测资料的分析结果相吻合。     

青藏高原泥石流的形成及运动过程研究

传统的泥石流模拟模型对青藏高原泥石流的模拟与实际情况的吻合度较低,无法为预防与治理泥石流提供合理的数据。为此,构建泥石流形成运动模拟模型对青藏高原泥石流形成及运动过程进行模拟研究。根据质量守恒原则、侵蚀、降雨与摩擦影响因素,建立泥石流形成、运动模拟模型,采用有限差分数值方法对泥石流厚度与流速进行计算。通过对泥石流厚度与流速的计算,实现了对青藏高原泥石流形成、运动过程的模拟。通过实验对比结果可知,泥石流形成及运动模拟模型与实际情况的吻合度远远高于传统模拟模型,说明泥石流形成运动模拟模型具备较高的有效性。     

泰宁县芦蓭坑沟“5.8”特大泥石流成因和特性分析

通过对2016年5月8日泰宁芦蓭坑沟泥石流灾害的现场调查,分析了芦蓭坑沟泥石流形成的物源、地形和水源条件,采用现场调查与模型计算相结合的方法分析了泥石流灾害的特征与形成演化过程。分析结果表明:本次泥石流为低频黏性暴雨型沟谷泥石流,沟口处泥石流流速达到11.7 m/s,泥石流流量达到721.7 m~3/s;极端雷暴雨是本次泥石流的激发因素,沟道复杂的地形地貌特征和丰富的松散坡积物为泥石流提供了演化条件;沟道内多处卡口和大石块堵塞放大了本次泥石流的规模和速度,沿途固体物质补给使泥石流容重逐步增大。通过分析芦蓭坑沟泥石流形成与演化特征,为类似低频泥石流灾害形成与演化提供一定的理论与技术支撑。     

不同上限粒径泥石流浆体的流变参数变化规律

根据云南东川蒋家沟黏性泥石流原样颗分资料,利用泥石流堆积物配置4个黏性泥石流原样对应的上限粒径分别为0.25、1、2、5和10 mm的浆体,通过球系统开展流变试验,利用Herschel-Bulkley模型拟合流变曲线,研究较粗的颗粒加入细颗粒浆体后流变参数的变化规律。结果表明各样品均表现为剪切稀化流体,粗颗粒加入细颗粒浆体后浆体屈服应力增加,剪切稀化程度减弱;同样颗粒级配下,浆体的屈服应力随固体体积浓度指数增加。由于流动性指数的变化,粗颗粒加入后浆体稠度指数的变化没有明显规律,但是表观黏度增加,增幅略小于屈服应力的增幅。粗颗粒浆体与细颗粒浆体的相对黏度和相对屈服应力之间存在显著的线性关系,可根据该关系式对泥石流原样的表观黏度进行估算。     

7月3日茂县棉簇沟特大泥石流成因和特征分析

通过对2011年7月3日的茂县棉簇沟泥石流灾害的现场调查,从物源、地形和水源条件入手,分析了灾害特征与形成演化过程.强降雨是本次泥石流的诱发因素,沟道内复杂的地形地貌特征为泥石流提供了演化和规模放大条件:(1)泥石流导致堰塞湖溃决,为泥石流提供了近1×104m3的水源,增强了泥石流的水动力条件,增加了沿途冲刷量;(2)沟道内多处基岩卡口和跌水放大了本次泥石流的规模和速度;(3)沿途固体物质补给使泥石流容重逐步增大.此次泥石流造成沟道微地貌改变,今后泥石流暴发的可能性和频率将会大大增加,高频率、中小规模泥石流将是今后该沟泥石流活动的特征.     

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。     

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。