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川藏公路南线板状湿雪雪崩形成机制与防治措施研究
Alternative TitleResearch on the Formation Mechanism and Control Measure of WetSlabSnow Avalanche in South Line of Sichuan-Tibet Highway
Language中文
刘大翔
Thesis Advisor程尊兰
2014
Degree Grantor中国科学院研究生院
Place of Conferral北京
Degree Name博士
Degree Discipline岩土工程
Abstract川藏公路南线(318国道)是西藏自治区交通大动脉之一,每年11月到次年5月公路沿线的季节性雪崩时有发生,令交通安全受到重大威胁。为实现公路保通,论文拟对川藏公路南线的雪崩发生机制及防治对策开展研究,进而为修建雪崩公路防护结构提供理论支撑。通过对公路沿线众多雪崩点的实地考察,判断川藏公路南线发生季节性雪崩的直接诱因是日照和降雨,且对公路威胁最大的雪崩类型为板状湿雪雪崩。通过查阅资料,论文首先对现有雪崩及其防治工程的研究进行了综述。其次,通过开展板状湿雪雪崩形成机制实验,得出了雪层抗剪强度与含水率的关系公式,以及雪层与典型粗糙下垫面间摩擦系数与雪层含水率的关系公式。最后,通过室内实验模拟了雪崩与公路典型防护结构的相互作用,建立了防护结构的受力计算模型,并修正了模型中的计算参数。论文的主要结论有: (1)对国际上常用的雪崩防治工程进行了分类,并重点按作用手段分类阐述了各种防治工程的研究与应用现状,对雪崩防治工程的研究进展、适用范围、设计要求、应用情况等关键问题进行了总结和探讨。研究认为,目前的雪崩防治工程存在修筑标准欠缺、雪崩机理不明确、工程设计参数不合理、试验模拟不理想、基础理论研究落后于实践活动等不足,并建议从工程综合配置、雪崩与防护结构相互作用、工程设计参数定量化研究、积雪清理技术开发、监测预警系统构建等方面开展先行工作。 (2)雪层与下垫面间结合层遭受剪切破坏是板状湿雪雪崩发生的主因,但雪崩还与积雪所在下垫面的类型(摩擦系数)有关。薄层积雪在下垫面上的粘附现象表明:板状湿雪雪崩的发生必须首先破坏雪层与下垫面间的结合层,再克服二者之间的摩擦力影响,方可触发雪崩。通过埋设在雪层底部的含水率传感器,确定了不论在人工光照还是降雨条件下,结合层的极限含水率均在80%左右。 (3)利用土力学中的摩尔库伦准则,重点分析了雪层含水率与抗剪强度、雪层含水率与雪层和下垫面间摩擦系数的变化规律,并通过回归分析和线性内插法,分别得出了雪层粘聚力与含水率的关系公式c=f(w),内摩擦角与含水率的关系公式φ=f(w),雪层和粗糙下垫面间摩擦系数与含水率的关系公式μ=f(w)。 (4)采用人工光照和降雨手段,研究了自由水在雪层中的渗透规律以及垂直方向雪层含水率的差异,发现底部雪层含水率最高,而其他位置的雪层含水率很小。此外,随着自由水的不断下渗,雪层底部会出现一层“持水层”。同极限含水率一样,持水层也存在极限高度,约为3cm,且该高度与渗透系数无关。 (5)受山坡与公路典型防护结构(防雪棚)间夹角的影响,山坡与防雪棚的结合部位有可能出现“停滞区”。论文分情况讨论了结合部位存在“停滞区”与不存在“停滞区”两种情况下防雪棚顶棚法向受力计算过程,并据此建立了防护结构受力计算模型。 (6)防护结构顶棚中,靠近山坡的1#受力区域是关键受力部位,该区域的法向受力峰值明显大于远离山坡的2#、3#、4#受力区域,且山坡坡度越大、防雪棚坡度越小、运动路径越长、雪崩颗粒粒径越大、磨圆度越好、雪层中含水率越大,则结构关键部位的法向受力峰值越大。此外,对结构受力三个组成部分的贡献率进行了分析,发现因动量改变所产生的作用力Fdyn的贡献率占主导地位,其次是雪层重力P和上游雪崩产生的被动压力P1,且P1的贡献率与Fdyn相比,有数量级的差距。 (7)参数β的取值对于预测防护结构关键部位受力有重要意义。根据参数β与各个实验变量间的关系对比结果,提出影响参数β取值的主要因素有:沟口位置雪崩运动速度、沟口位置雪崩最大厚度与粒径的比值、山坡坡度、山坡与防护结构顶棚间的夹角。通过量纲分析和回归分析,得出了参数β的无量纲预测公式; (8)根据实地考察、理论分析以及实验结果的综合考虑,建议对现有防雪棚的顶棚、横梁、外纵梁以及顶棚与山坡的结合部位分别采取相应的构造改进措施。此外,为减小防雪棚受到的切向力,顶棚应及时清理并尽可能采用摩擦系数小的材料
Other AbstractSichuan-Tibet highway south line (State road 318) is one of the traffic artery in Tibet autonomous region. Every November to next May, seasonal snow avalanches along the highway occur frequently, so that traffic safety is under threat. The dissertation intends to research snow avalanche formation mechanism and countermeasures along Sichuan-Tibet Highway south line so as to provide theoretical support for the construction of highway protection structures. Through surveying numerous snow avalanche points along the highway, it can be determined that the direct cause of seasonal snow avalanche in this region is sunshine and rainfall, and the greatest threatened type is plate-wet snow avalanche. The dissertation firstly reviewed current research about plate-wet snow avalanche and appropriate control measures. Then, by carrying out an experiment about formation mechanism of plate-wet snow avalanche, the relationship formula between shear strength and moisture content of snow layer can be got, and the relationship formula between friction coefficient of typical rough underlying surface and moisture content of snow layer can also be got. Finally, through laboratory experiment to simulate the interaction between snow avalanche and typical highway protection structure, we established the force calculation model of structure and revised an important parameter in the model. The main conclusions of the dissertation can summarized into eight points: (1)In this dissertation, some international commonly used prevention and control technologies are classified. The research progress, application scope, design requirement, application situation of these technologies are summarized and discussed. What’s more, the paper points out that there are some shortages such as lack of construction standards, avalanche mechanism is not clear, parameters calculation of engineering design is unreasonable, the effect of test simulation is not perfect, the basic theory research is behind the practice activities and so on. Finally, the paper proposes several aspects for future research. (2)The main reason of plate-wet snow avalanche is the binding laying between snow layer and underlying surface is suffered shear failure, another factor is friction coefficient between snow layer and underlying surface. The adhesion phenomena about a thin snow layer on a granite slate shows that plate-wet snow avalanches occur must first destroy the bonding layer between the snow layer and the underlying surface, and then overcome the effects of friction between the two. Through moisture content sensors laying at the bottom of the snow layer, it can be determined that the extreme moisture content of binding layer is about 80%. (3)By using mole Coulomb criterion and regression analysis method, we got the relationship formula between cohesion and moisture content of snow layer (c=f(w)), the relationship formula between internal friction angle and moisture content of snow layer (φ=f(w)), the relationship formula between friction coefficient of typical rough underlying surface and moisture content of snow layer (μ=f(w)), respectly. (4)We researched the infiltration law of free water in the snow layer through artificial sunshine and rainfall and found that there is a water-holding layer at the bottom of snow layer. The height of water-holding layer is about 3cm and has no association with the permeability coefficient. (5)Affected by the angle between hillside and snow shed, the combined site of hillside and snow shed may appear dead zone. Based on this standpoint, the dissertation discussed force calculation process of snow shed in both cases and established the analysis model of interaction. (6)1# force area , whose force peak is much greater than 2-4# force area in the experiment,is the key part of snow shed. The force peak is proportional to the slope of hillside, the motion path length, moisture content and particle size of snow avalanche, but inversely proportional to the slope o
Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/7895
Collection山地灾害与地表过程重点实验室
Recommended Citation
GB/T 7714
刘大翔. 川藏公路南线板状湿雪雪崩形成机制与防治措施研究[D]. 北京. 中国科学院研究生院,2014.
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