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动床条件下泥石流阻力特性的实验研究
Alternative TitleExperimental study on the resistance of debris flows over an erodible bed
Language中文
田密
Thesis Advisor胡凯衡
2013
Degree Grantor中国科学院研究生院
Place of Conferral北京
Degree Name硕士
Degree Discipline防灾减灾工程及防护工程
Keyword泥石流 运动阻力 定床 动床 床沙输运 物质交换 阻力计算公式
Abstract泥石流的运动阻力是泥石流动力学的核心内容之一,也是泥石流防治工程规划设计的重要参数。泥石流阻力参数的选取决定了泥石流的设计流量、防治工程的规模,最终会影响工程的投资成本。自然界中泥石流沟往往不是基岩,而是覆盖有巨厚的松散堆积物。泥石流通过松散物质覆盖区时,因其强烈的挟沙能力,会侵蚀冲刷沟床,沿程不断地携带床沙,从而将其变为推移质或悬移质进入泥石流体。这个过程中泥石流与沟床床沙间动态的物质交换会直接影响泥石流的阻力,使得泥石流的运动阻力特性不同于一般定床情况。论文在野外观测现象的基础上,初步探索了野外泥石流沟的动床阻力,得到了床沙输运与泥石流运动阻力的关系。然后开展了室内水槽实验,重点研究动床条件下泥石流的阻力特性。通过改变水槽坡降、泥石流容重和沟床床沙级配,一共进行了50组泥石流定床和动床水槽实验。泥石流动床阻力的研究,能为泥石流动力学研究提供一定的科学参考价值,也为泥石流防治工程设计提供理论依据,对泥石流的防灾减灾具有重要的意义。论文主要研究成果如下: (1)根据野外泥石流沟的调查数据,初步分析了床沙输运与泥石流运动阻力的关系。泥石流携带的床沙越多,阻力损失越大,并且阻力随弗劳德数的增加而减小。泥沙输运要消耗一部分能量,泥沙输运过程中泥石流固体颗粒间、泥石流与床沙颗粒间相互碰撞与摩擦,都会造成能量的耗散。(2)泥石流通过动床时,龙头紊动强烈,呈典型的逆坡型,龙头对床沙产生一定冲击作用,使床沙跃起后进入泥石流体。高速运动的龙头和静止不动的动床床沙间存在一个较大速度的梯度,致使泥石流与床沙间进行物质和能量的交换。(3)当来流条件相同时,动床条件下泥石流泥位显著大于定床条件,且变幅大。相同性质的泥石流在不同的外界条件下,沟床床沙会影响其运动特性。(4)据水槽实验数据,对比泥石流定床和动床阻力得到,泥石流与床沙间动态物质交换会消耗能量,使得泥石流的动床阻力显著大于定床阻力。(5)影响泥石流动床阻力的因素可归纳为三方面:泥石流体自身条件、边界条件以及物质交换。综合泥石流阻力的影响因子,将实验数据经多元回归分析建立了动床条件下泥石流运动阻力的计算公式,即。新公式考虑了动床的影响,比国内最具代表性的康志成和费祥俊公式更能反映泥石流在动床上的阻力。
Other AbstractDebris-flow resistance is a core content of debris flows dynamics and an important parameter for the design of mitigation measures in calculating flow velocity or flow discharge, finally determining the scale and the cost of the control engineering. Debris flow ditches in nature are often not the bedrock, but covered with thick loose debris. When going through the loose material covered areas, because of its strong carrying capacity, debris flows would erode and scour the bed materials and entrain bed sediment, thus making them become the bed load or suspended load into the debris flows. The dynamic mass exchange of material between debris flows and the bed materials will directly affect the resistance of debris flow, so the characteristics of debris flow resistance is quite different from that under general rigid bed conditions. On the basis of field observation, this paper first makes a primary research on the relationship of the entrainment of bed sediment with the debris-flow resistance. Then it focuses on the experimental study of debris-flow resistance over erodible bed. By changing the flume slope, debris flow density and the bed material gradation, 50 contrast flume tests are conducted in the article. The following main conclusions were obtained: (1) Based on the field survey data of debris flow gullies, preliminary study of the relationship between the sediment transport and debris-flow resistance suggests that the debris-flow resistance increases along with the increasing entrainment of bed sediment and decreases with the increase of the Froude number. In the process of sediment entrainment, great energy is consumed by bed sediment transport and collision and friction between solid particles and bed particles. (2) Flume experiments found that as the debris flow went through the erodible bed, the turbulent head is a typical inverse slope type and the front is in a high-speed motion state, while the erodible-bed materials are stationary. Thus the great velocity gradient between the high-speed head and the stationary bed sediment results in mass exchange between the debris flow and the bed materials. At the same time, the turbulent head has direct impacts on the erodible bed making the bed sediment jump into the flow. (3) Movable-bed experiments illustrate that under the same flow conditions the flow depth over erodible bed is significantly greater than that over the fixed bed, and there are quite big changes in the erodible-bed depth. It indicates that the kinetic characteristics of the same debris flow but in different external conditions change significantly. (4) According to the flume tests, through comparing the erodible-bed flow resistance with the rigid-bed flow resistance, it makes clear that because of great energy consumption during mass exchange, the erodible-bed resistance is greater than the rigid-bed resistance. (5) The influencing factors of the debris-flow resistance can be summarized as three aspects: the effects of debris flow itself, boundary condition and the entrainment of bed sediment. Taking into account all these factors, a new formula estimating the erodible-bed flow resistance is derived from multiple regression analysis, . The calculated results presented a good agreement with the observed data by comparing with other formulas.
Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/7036
Collection山地灾害与地表过程重点实验室
Recommended Citation
GB/T 7714
田密. 动床条件下泥石流阻力特性的实验研究[D]. 北京. 中国科学院研究生院,2013.
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