【作者】 马栋和；

【导师】 王常明；

【作者基本信息】 吉林大学 ， 地质灾害防治工程， 2012， 博士

【摘要】 黄土在我国分布十分广泛,近年来随着经济建设的发展和对外开放的需要,高等级公路的修建速度加快,穿越复杂地形地貌区域的增大,随之带来的公路工程边坡问题也日益增多。由于黄土的特殊性质(大孔隙比、低压实度、弱抗水性、高透水性、湿陷性),决定了其抵抗径流冲刷特别弱的固有特性,加之公路的斜坡地形为坡面径流的冲刷提供了良好的动力条件,因此公路边坡冲刷破坏防治一直是黄土公路地区土的重要研究课题。现行《湿陷性黄土地区建筑地基规范》(GB50025-2004)首次将辽宁西部列为黄土边缘区,目前仅有少数学者对该地区的黄土进行了初步研究。为此,作者结合国家自然科学基金面上项目“辽西地区黄土边坡坡面冲刷破坏机理的研究”(No.40972171),以辽西黄土边坡为研究对象,通过土质学、土力学和水力学多学科有机结合的途径,研究黄土边坡坡面冲刷破坏的水土力学机理。论文共分八章,第一章介绍了选题依据与研究意义,黄土边坡坡面侵蚀破坏特征及机理研究现状,给出了论文的研究内容与技术路线。第二章为辽西黄土的工程地质特性,主要对辽西地区的黄土的分布规律和成因、黄土的物质组成、土化学特性、黄土的微观结构特征及其定量化、黄土的基本力学性质及湿陷变形规律等方面进行了深入的研究。第三章为黄土边坡坡面冲刷室内模拟试验研究。深入研究降雨条件下黄土边坡坡面冲刷破坏过程及其特性,自行研制了小型边坡降雨及观测装置,开展室内边坡降雨冲刷破坏模拟试验。主要研究不同坡度的边坡在3个降雨级别下坡面的冲刷破坏规律、降雨入渗规律、孔隙水压力变化规律、颗粒运动及坡面形态的细观变化特征。第四章主要通过现场调查与室内物理试验模拟结果,研究坡面冲刷破坏特征与影响坡面冲刷破坏的主要因子及其相互作用。第五、六章是在模型模拟试验和现场调查监测的基础上,采用SEEP/W及PFC2D进行数值分析,进一步研究坡面冲刷过程中土颗粒受力特征、降雨入渗规律,进而揭示冲刷破坏的微观机制。第七章为结合坡面侵蚀的3个动力学子过程：雨滴溅蚀及产流、径流引起的土体颗粒分离以及颗粒的输移,研究坡面颗粒启动机制,量化研究边坡侵蚀、深入分析(从微观和宏观)坡面冲刷破坏机理。第八章为结论与展望,总结本文所得到的结论及创新点,并提出进一步研究和改进的建议。论文紧密围绕“黄土边坡冲刷破坏的机理”这一中心问题,采用物理模拟、数值分析等方法、定性和定量相结合的途径,对黄土边坡坡面冲刷破坏的全过程特征进行了研究,基本明确了黄土边坡坡面冲刷破坏的机理,初步建立了黄土边坡冲刷破坏的计算模型,成果对深化黄土边坡冲刷破坏的研究及黄土边坡防护设计具有重要的意义。限于作者水平,许多问题尚有待于进一步研究,不当之处敬请各位专家学者批评指正。更多还原

【Abstract】 A study of water-soil mechanics coupling mechanism and model for loess slope surface erosion on highwayHighway slope erosion and failure is a phenomenon caused by rainfall and soils will be taken away from the slope sutface, which can destroy subgrade and cutting slope. Slope erosion will cause a plenty of soil and water loss, collapse at slope shoulder, slope erosion hydraulic drop, scouring at toe of a slope and surface erosion furrow. If the surface erosion develops further disasters such as collapses and landslides will take place, which will have adverse effect to normal operation of highway and will deteriorate ecological environment. Loess in study area has a different geological characteristics and water sensitivity from Northwest areas, thus the loess slope erosion becomes a prominent issue in Road-slope Project. By taking the slope in loess highway as the research object, by means of combining with field investigation and physical simulation, the physical composition, structure of loess and its collapsible deformation behavior are studied. The main factors influenced on slope erosion damage are analyzed and the micro mechanism of slope erosion damage from soil mechanics and hydraulics. Then water-soil mechanical and mathematical models are constructed and their corresponding slope stability analysis method is set up. This study can enrich and improve the theory of loess slope erosion damage calculation, and can provide scientific basis for the design and protection of highway slope in western Liaoning. Many main results and achievements of this staudy are obtained as follows:(1) Loess in study area is formed mainly by aeolian effect and water plays a secondary role. The content of silt with particle size of0.05-0.005mm were72.87%. The main mineral component is detrital minerals, and contains a certain clay minerals. Soluble salt in the region is mainly chloride and dicarbonate, contains a small amount of sulfate. In a depth of20m, there are four microscopic structure types from top to bottom:scaffold-macrospore micro-cementation structure, scaffold-macrospore-mosaic micropore semi-cementation structure, flocculated cementation structure, coagulate cementation structure. Collapsibility coefficient is in the range of0.010to0.108in Western Liaoning, mostly of the Grade Ⅰ～Ⅱ non-collapsible, locally with a collapsible, and initial moisture content has a significant impact on collapse deformation.(2) Three-dimensional digital images of loess microstructure surface are established by extracting gray information of SEM images. A new method of average fractal dimension calculation to determine the fractal dimension before and after collapse. The results show that the fractal dimension of loess is2.508before collapse and it is2.590after collapse. The micro-structure surface undulation increases, as well as the complexity of the pore.(3) Slope erosion damage features can be divided into three stages, namely, splash erosion and laminar flow erosion, gully erosion and general demolition. The procedure from rainfall erosion and failure includes a series of actions such as splash erosion, infiltration, surface erosion, rill erosion, shallow trench erosion, gully erosion, scouring erosion, collapsed and sliding. Th slope will failue from the initial splash erosion and sheet erosion under a lower intensity to medium-term gully erosion under a high intensity, and finally leading to the multi-way damage stage of collapse, overall sliding. According to the field investigation and laboratory simulation observation, cross-sectional shape of highway slope gully erosion can be divided into V-shaped, U-shaped, trapezoidal, triangular and airfoil.(4) The major impact factors on slope erosion are studied. The results show that as rainfall intensity increases, the slope erosion damage is getting worse in the circumstances of continuous increasing rainfall. The critical gradient range of highway slope erosion in western Liaoning is between36.5°and44°. Rainfall erosion is the most serious within the scope of critical gradient. For different slopes, succession of the flow erosion mode and gully erosion cross-section shape will be different. Erosivity will enhance with the increases of slope length and the rainfall rechange region, which would increase the runoff potential significantly. Loess in this region possess characteristics such as vertical joints and large-pore structure, strong permeability, high soluble salt content, cement dissolution failure when saturated, so the cohesion reduces significantly.(5) The rainwater infiltration depth gradually increases with raifall time. The rainwater saturation line on the slope is not parallel to the slope line, but presents regularity the upper superficial and the lower dark. Aided by softwares SEEP/W and PFC2D simulation, it can be concluded, from the physical experiment moisture content dynamic monitoring, that for slopes with a small angle, pore water pressure grows fast at the foot of the slope, and the water content increasing rate turns to be greater than the top of the hill. The strength among grains decreases obviously at toe, soil particles startup under multiple external forces and the toe toe begin to damage. For slopes with a larger angle, even though the development regularity of saturation line is insignificant, pore water pressure increases rapidly and the moisture content grows fast on the top. At this time the top firstly occurs damage due to soil particles was washed away by runoff. To the same slopes, saturated time of surface soils will shorten with the increase of rainfall. Meanwhile the overland flow produces rapidly, flow will expand in the slope, rainwater infiltration rate will increase, and slope erosion damage becomes heavier.(6) Highway slope erosion in western Liaoning can be divided into three dynamic processes, namely, raindrop splash erosion and runoff, soil particle separation caused by runoff and the particles transport. Soon after it rains, infiltration rate is larger, surface runfall will not yet produce on slope. Raindrops hit the slope surface, which was mainly dry soil, small particles are splashed. With the accumulation of infiltration, the infiltration rate begins to decrease. Until the moisture content reaches the natural water-holding capacity, it turns to the fill runoff q. Overland flow q will become a sheet flow along the slope surface, and the soil particles present layered erosion. When the flow rate q is close to qc, layer flow will no longer be able to maintain due to characteristic fluctuation of the underlying surface, and the gully erosion begins. As hillslope erosion pattern turned into rill erosion from sheet erosion, the erosion amount will be doubled or even dozens of doubling. Pooling and transport of particles is the last basic dynamic process of soil erosion. Since sediment is always pooled by the slope and transported to the toe, which process is similar to the generation and convergence of small drainage networks, we can get the entire convergence and sediment transport process with the help of river model as well as the water movement and sediment dynamics description.更多还原