【作者】 何玉琼；

【导师】 徐则民；

【作者基本信息】 昆明理工大学 ， 工程力学， 2013， 博士

【摘要】 滑坡、泥石流等地质灾害在世界范围内广泛存在,对人民的生命财产安全造成不可忽视的影响。斜坡在重力、水文条件、地震力、人类活动、地质营力等因素的作用下不断发生变化,使斜坡内部原有的应力状态发生改变,导致斜坡土体发生不同形式的变形与破坏。本文综合植被斜坡水文、降雨入渗、蒸腾、截留、植被类型、植被根系、地形坡度等因素对斜坡稳定的贡献进行定量分析。在了解和掌握植被斜坡变形及破坏发生、发展规律的基础上,研究植被对斜坡稳定的作用机理与特性；研究降雨在斜坡非饱和带中的渗透过程及机理,充分认识植物及其根系与斜坡之间的作用机理；研究植被斜坡在降雨量达到一定值(临界降雨量)时,植被与水-岩、岩土体相互作用下斜坡的极限平衡状态；分析植被对斜坡稳定的贡献及作用。因此,本文主要围绕以下几方面进行研究：(1)研究非饱和带土中的植被根系、有机质土对水渗透性的影响,分析水在土中的渗透路径与特性。在非饱和带中土壤的颗粒、团粒结构与植物根系、虫子分泌物及微生物的相互作用,有的表现出亲水性,而有的则表现为是憎水性,这将导致水在土中的流动路径不一致,使亲水性团粒中汇集较多的水,而憎水性团粒中即使土体较干燥也不会有过多的水分渗入,从而使斜坡土体中的含水量不一致。(2)借助于扫描电子显微镜(SEM)技术,分析土的团粒结构及孔隙结构。从SEM图中可以看出：斜坡地表附近的土壤结构十分疏松,含有大量腐质的枯枝落叶、植被根系及有机质的团粒结构,可见相互连通且形状各异、向不同方向延伸的裂缝与孔洞；地表以下3-8cm位置可见大量的团粒结构,团粒之间形成一些不规则、形状各异的孔洞,有的孔洞有连通的趋势,发展成网状结构通道,并可见腐质中空的根孔,根孔外侧与土体之间有明显的缝隙,土层结构较表层土质致密；8cm以下土层也见大量的团粒结构,团粒结构周围也出现大量相互连通的孔洞,并见树根及草根腐烂后形成较大的通道,土质较上一层密实。(3)观察植被根系在土中的分布形式、范围、深度及植被根系在斜坡岩土体中的有效作用深度；分析植被根系在水的作用下对斜坡稳定的作用；研究在降雨条件下植被与斜坡岩土体的作用机理及特性,植被根系与水-岩、岩土体的相互作用及特性。在一定降雨条件下,如果降雨入渗量达到了一定的程度,虽然植被根系可以在一定深度范围内固坡,但是植被的根系达到斜坡体潜在滑动面的量数不多,并且植被根系与岩土体之间的作用力已减弱,植被对于斜坡体而言是使斜坡体下滑的一个分力,植株越高其自重越大,植被的自重增加了斜坡体的荷重,并向斜坡传递风的动力荷载,在风载与植被自重的作用下,植被的存在只能加剧斜坡体的滑动,增加斜坡体的不稳定性。(4)研究植被斜坡降雨期间的蒸散发与截留方式,监测与计算降雨期间的蒸发量与植被截留量,分析植被对斜坡水文的影响。分析降雨条件下水循环的基本规律,及植被斜坡的孔隙水压力、孔隙率、渗透系数等因素对坡面径流和渗流的影响,植被通过截留作用降低了到达地面的降雨强度和有效雨量,使其击打坡面的机会大大降低,减小了击溅侵蚀强度,对控制侵蚀和保护坡面有重要意义。(5)研究降雨在非饱和带中的入渗过程与机理,降雨湿润前锋几何形态与迁移过程。降雨期间,雨水渗入土体并在非饱和带重新分配,分配过程取决于土体的水分条件、水压力、与非饱和渗透性。降雨刚开始的时候土体具有极高的渗透能力,降雨将全部渗入土中；随着降雨入渗过程的持续进行,土体的渗透能力逐渐减弱,直到入渗率达到一个稳定值为止。当降雨入渗使土体饱和推进湿润锋时,如果降雨强度大于土的渗透系数,大量的地表水进入土体,地下水位将会上升,水的推进将导致地表附近的土壤吸力减少,含水量增大,土的强度降低,重度增大,从而使滑面上的剪应力增大。随着降雨时间的延长,降雨入渗量逐渐增多,孔隙水压力逐渐上升,边坡的稳定系数逐渐减小。在长期渗透作用下,地表发生失稳是因为存在正的孔隙水压力或负的孔隙压力以及吸力减少。当雨水入渗通过不饱和区域时,湿润前锋附近的斜坡表面在长期降雨作用下可能导致失稳,这种失稳通常是平行于坡面的浅层破坏。(6)建立相应的斜坡水文稳定模型,结合现场勘察、监测数据以及斜坡岩土体主要特性、地形地貌、降雨强度与降雨持续时间、地下水位等因素,计算稳定系数小于1的潜在滑动斜坡单元数量与各斜坡单元的临界降雨量,在DEM的基础上对斜坡稳定进行可视化分析与预测。斜坡失稳与降雨量大小有关,但同时也与降雨持续时间及过程有关。一种情况是降雨量极大但持续时间较短,一部分雨水未来得及转化成地下水而流走,产生坡面径流,这一部分雨水对滑坡的贡献不大,不一定产生滑坡；另一种情况是降雨量虽然不大,但持续时间较长,降雨强度小于土体的入渗能力时,雨水能充分的渗入到土体中,一定时间内总的渗入量较大,可能会产生滑坡。降雨强度与历时决定降水渗入量的大小,对斜坡稳定的影响较大。计算结果表明：位于楚勐公路路基下方的斜坡单元在降雨量为0～50mm/d范围内已连成片,该位置可能产生整体滑动；而斜坡其他单元未连成片,由于斜坡单元土体之间的相互牵制作用不会产生大面积的滑动,但局部单元会产生面表剥落等现象。潜在滑坡单元数量随降雨量的增大呈上升趋势,较陡地形产生滑坡的可能性较大。(7)在考虑蒸散发量与截留量、降雨入渗的作用下,运用降雨阈值模型模拟斜坡单元在不同降雨条件下产生潜在滑坡单元的位置与现场滑动位置基本一致,吻合率达80%以上。说明运用降雨阈值模型预测模拟斜坡产生潜在滑动时所需临界降雨量与进行斜坡稳定性分析是可行的。监测到的地表及地下位移滞后于降雨时间,各监测钻孔的地下水位随降雨持续时间的增加呈上升的趋势,并且水位上升时间滞后于降雨时间。最后,对本文研究成果进行总结。由于产生滑坡与泥石流的斜坡多为植被斜坡,研究植被斜坡在降雨条件下的稳定性具有一定的现实意义,为预测、预防滑坡、泥石流等自然灾害提供相应的理论依据。更多还原

【Abstract】 Landslide, Debris flow and other geological disasters was widespread in the world, that the impact for the safety of people’s life and property can’t be ignored. The effect of gravity, hydrological condition, earthquake force, human activities, geologic forces and other factors that slope is changed constantly, so that the slope body original stress state is changed, leading to different forms of soil deformation and failure.This paper carries on the quantitative analysis for slope stability, combining the factors such as vegetation slope hydrology, rainfall infiltration, evaporation, interception, vegetation types, vegetation roots, topography&slope. Based on understanding and mastering of vegetation slope deformation and failure law of development, the effect mechanism and characteristics of vegetation to slope stability are studied, the penetration process and mechanism that rainfall on slope unsaturated zone are studied, the mechanism between the plant and its roots and slope are fully understand, the limit equilibrium state of slope under vegetation and water-rock, rock and soil interaction when vegetation slope in rainfall reaches a value (critical rainfall) are studied, the contribution and effect for vegetation to the slope stability are analyzed. Therefore, this paper focuses on the following:(1) The effect of vegetation roots and organic soil in unsaturated zone for the water permeability is studied, the water’s infiltration path and characteristics in the soil is analyzed. It’s interactions of the soil particles, granular structure with the vegetation root, worm’s secretions, and microbial in the unsaturated zone, some exhibit hydrophilic, while others appear to be hydrophobic. This will lead to the flow path is inconsistent in the soil, making hydrophilic aggregate together more water, and hydrophobic aggregates won’t have too much moisture penetration even the soil is dry, so that the water content is not consistent of the slope.(2) Applied scanning electron microscope (SEM) technology, analysis of soil aggregate structure and pore structure. From the graph of SEM:the soil structure near the surface of slope is very loose, containing a large number of litter, vegetation roots and organic aggregate structure, there are a lot of the fractures and pores that connectivity and variable shape, extending into different directions. Below the surface of3-8cm showed a large amount of aggregate structure, between the aggregate yielding some irregular, in different shapes of the pores space, some with trend of development, form a mesh structure channel, and visible detritus hollow bore of the root, between the lateralof root and soil have obvious gap, compared the surface soil, it’s structure to be densified. Below the surface8cm also have a large number of aggregate structures, around the aggregate structure emergence a large number of interconnected pores, and have some roots and large channel that the root rot formation, root hole and the soil have obvious gap, compared the upper layer of soil is dense.(3) Observation of the distribution form, scope, depth and effective interaction depth of vegetation roots in the soil. Under the action of water, the effect of vegetation roots to slope stability is analyzed. Under the condition of rainfall, the mechanism and characteristics of the vegetation and the rock-soil of slope, the interaction and characteristics of vegetation roots and water-rock, rock-soil are studied. Under certain rainfall conditions, if the rainfall infiltration reached a certain level, although the vegetation roots can be reinforcement the slope in a certain depth range of slope, the number of vegetation roots to the potential sliding surface of slope is less, the interaction between vegetation roots and soil has weakened, vegetation is a sliding force that made slope slid, the higher of the plant that it’s self-weight is the greater, which increased the slope body load, and transfer the wind load to slope, under the action of wind load and plant self-weight, vegetation exists only exacerbated the slope sliding, increase the slope instability.(4) Evapotranspiration and interception of the vegetation slope during rainfall are studied, monitoring and calculating the evaporation and interception of vegetation during the rainfall, the effect of vegetation for slope hydrological is analyzed, the basic law of rainfall water cycle is analyzed, and the effect of the runoff and infiltrate of the factor, such as pore water pressure, porosity, permeability coefficient and other factors of vegetation slope are analyzed. The effect of vegetation interception reduces rainfall intensity and effective rainfall that reach the surface, the hit chance and the splash erosion to slope is reduced greatly, that is important to the erosion control and protection of slope.(5) The rainfall infiltration process and mechanism, wetting front geometry and migration process in the unsaturated zone are studied. During the rainfall, rainfall infiltration and redistribution in unsaturated soil, the redistribution process depends on the soil moisture, water pressure, and unsaturated permeability. At the beginning of rainfall, soil with high penetration ability and all the rainfall infiltration into soil. With the process continues, the soil infiltration capacity decreased gradually, until the infiltration rate to reach a stable value. As the soil is saturated with the rainfall infiltration then promote wetting front, if rainfall intensity is higher than the soil hydraulic conductivity that lead to large amount of rainfall into the soil, underground water level will rise, the soil suction is reduced, increasing water content, the strength of the soil is reduced, increasing unit weight of soil, so that increasing the shear stress of slide surface. Along with rainfall time that rainfall infiltration is increasing gradually, the pore water pressure is rising gradually, the slope stability coefficient is decreasing gradually. In the long term infiltration, surface instability is due to the presence of the positive pore water pressure or negative pore pressure and suction to reduce. When the rain infiltration through the unsaturated zone, the surface of the slope near wetting front could lead to instability in the long-term rainfall, which is usually parallel to the slope. (6) To establish the corresponding slope hydrological stability model, Combining with field investigation and monitoring data, and the main features of the slope rock-soil mass, topography&geomorphology, rainfall intensity and duration, underground water level and other factors, the stability coefficient is less than1of the potential sliding slope unit number and the critical rainfall for the slope unit are calculated, Based on digital elevation model (DEM) could realize the visual analysis and prediction of slope stability. Slope instability in relation to rainfall, also in relation with the rainfall duration and the processes. In a situation that rainfall great but short duration, a part of the rainwater could not translate into groundwater flow, produce surface runoff, which on landslide contributed little, not necessarily a landslide. Another situation is that rainfall is small, but longer duration, rainfall intensity is lower than the soil infiltration capacity, rainwater can full infiltration into soil, within a certain period of time the total penetration is larger, may be produce landslide. Rainfall intensity and duration decided to rainfall infiltration quantity, which influence the slope stability. The calculation results show that the slope unit which located in the Chu-Meng highway beneath subgrade in the rainfall range of0-50mm/d has become a whole, the location may be integral sliding, While other unit of the slope is not connected, due to the mutual restraint effect between the soil of slope unit, does not have a large area of the slide, but local unit generates the surface spalling phenomenon. Potential landslide unit number with amount of rainfall assumes the trend of escalation, steep terrain landslide probability.(7) Considering the evapotranspiration, interception, and the effect of rainfall infiltration, under different rainfall conditions simulation the slope potential landslide unit by the rainfall threshold model, the simulation fits the real slope instability cases very well, the anastomosis rate with the actual landslide position more than80%.It is feasible that predictive simulation the required critical rainfall when the slope generating potential sliding and slope stability analysis by rainfall threshold model. Monitoring to the surface and underground displacement lag the duration of rainfall, with the rainfall duration increasing, the groundwater level of the monitoring borehole is rising, and the groundwater level rise time lags the rainfall time.Finally, summarizes the research results. Due to the slope that generates landslide and debris flow most is the vegetation slope, vegetation slope stability under rainfall condition is studied that has the certain practical significance, for the prediction, prevention landslide, debris flow and other natural disasters to provide the corresponding theoretical basis.更多还原