【作者】 张家明；

【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】 二十世纪中期以来,在日益加剧的全球变暖趋势的强烈驱动下,极端强降雨事件及与之相伴的山区流域植被发育斜坡群发性失稳事件的发生频率越来越高,因此对该问题深入研究具有重要的现实意义。截止目前,对降雨诱发型滑坡的研究主要集中在并无直接关系的降雨事件与滑坡事件及斜坡岩土体水岩相互作用方面,而对地下水对降雨的响应过程和响应机制的研究没有得到足够重视。地下水对降雨响应的第一发生环节是土壤水对降雨的响应,土体结构是影响该响应过程的重要因素。天然植被发育斜坡非饱和带土体中存在各种大孔隙结构,但既有斜坡土体降雨入渗研究多未考虑大孔隙的影响,因此植被发育斜坡土体降雨入渗研究已成为系统理解地下水对降雨响应的瓶颈。因此,本文采用现场亚甲基蓝染色示踪渗透试验法、碘-淀粉可视化方法、理论分析和有限元软件HYDRUS-2D数值模拟分析植被发育斜坡非饱和带土体大孔隙对降雨入渗的影响研究。本文完成的主要工作和取得的主要成果如下：1、对呈贡段家营试验区和昭通头寨沟试验区植被发育斜坡土体的物理、化学和水力特性进行了室内试验和现场试验研究。试验结果表明：植被发育斜坡土体的含水率和总孔隙率一般比裸坡土体和耕作土壤大,而容重和比重一般比裸坡土体和耕作土壤小：植被发育斜坡土体有机质含量比耕作土壤多；植被发育斜坡土体的给水度和饱和导水率总体随深度增加而减小,其中饱和导水率普遍大于裸坡土体和耕作土壤。2、选择亚甲基蓝作为染色示踪剂,在植被发育斜坡非饱和带开展染色示踪渗透试验,研究植被发育斜坡非饱和带土体大孔隙类型、大孔隙流路径分布模式及植被根系、有机质、土壤颗粒尺寸分布和土壤动物对大孔隙流路径分布模式的影响。研究得出以下结论：植被发育斜坡土体大孔隙主要有植被根系通道(有根皮腐烂根系通道、无根皮腐烂根系通道和根-土间隙),动物通道、洞穴,团聚体间大孔隙和砾-土间隙,其中根-土间隙是最主要的大孔隙；植被根系显著影响大孔隙流路径数量、尺度和分布特征,尤其是铅垂向下和顺坡向下的根系,当根系尺寸增大时,其对大孔隙流路径影响更显著；有机质有利于团聚体间大孔隙的形成；黏粒、粉粒和砂粒对大孔隙流路径形成没有积极功效,但砾粒有利于大孔隙路径形成,尤其是在表土层；土壤动物区系对动物通道网络形态的影响与动物生活习性和土壤质地、根系分布情况有关。3、采用碘-淀粉可视化方法和聚类分析方法研究植被发育斜坡非饱和带水流路径分布模式。试验结果表明：从地表垂直向下,强降雨条件下植被发育斜坡水流路径分布模式异质性逐渐增大；水流路径在顺坡方向的异质性比垂直方向的异质性大。4、土壤水运动理论研究表明非饱和土壤水运动理论有两次质的飞跃发展,但既有大孔隙流模型研究主要针对农业土壤,不适用于研究植被发育斜坡大孔隙流问题。本文提出植被发育斜坡非饱和带土体根-土间隙大孔隙流的概念模型。5、基于染色示踪渗透试验、水流路径示踪试验和既有相关研究成果讨论植被发育斜坡大孔隙对降雨入渗的影响。研究得出如下主要结论：植被发育斜坡非饱和带土体大孔隙主要通过截留地下暴雨径流而产生大孔隙流,快速增加降雨入渗进入土体的面积,加速降雨入渗；树干径流也能快速进入土体深部；土壤动物通道或土体的饱和导水率、入渗率与动物通道的生物量、总面积、长度和体积呈正相关关系,而与通道的连通性关系不显著；砾-土间隙截留地下暴雨径流或其他类型的大孔隙流,提高土体降雨入渗能力；植被根系通道对降雨入渗的影响远大于土壤动物通道；大孔隙网络系统的非均匀性导致土体含水率空间分布异质性。6、采用有限元软件HYDRUS-2D模拟分析相同降雨条件下,有无大孔隙、大孔隙直径、长度、弯曲率、密度和轴向对植被发育斜坡降雨入渗的影响。分析得出以下一些结论：植被发育斜坡土体大孔隙加快降雨垂直入渗,减弱表土层地下径流,延缓表土层出现暂态饱和区的时间,导致湿润前锋形态不规则；单根大孔隙直径变化对斜坡剖面含水率分布、压力水头分布和湿润前锋形态影响不大；大孔隙直径增大,优先流流速减小,大孔隙积水响应时间(稍微)推迟,有压入渗面积增大致使大孔隙内积水消散更快；大孔隙长度增大,斜坡剖面湿润前锋形态越不规则,降雨入渗深度越深,延缓大孔隙底部积水响应时间,大孔隙内积水高度减小,大孔隙长度对优先流流速没有显著影响；大孔隙弯曲率增大,其内部积水响应时间先增大后减小,降雨垂直入渗深度减小,大孔隙内积水长度增加,优先流最大流速先增大后减小；大孔隙弯曲率对湿润前锋形态的影响主要在降雨初期,随着弯曲率增大,湿润前锋形态不规则性逐渐减小；大孔隙群密度增大,湿润前锋形态越复杂,降雨下渗越快,大孔隙积水响应时间延缓,大孔隙之间的相互作用越显著；大孔隙群轴向与斜坡倾向之间的夹角减小,斜坡坡面湿润前锋形态不规则性减弱,优先流最大流速增大；当大孔隙位于表土层且大孔隙轴向与斜坡坡面近似平行时,大孔隙不利于降雨入渗。更多还原

【Abstract】 Since the mid-twentieth century, because of the ever-increasing global warming, the frequency of extreme intense rainfall events and well vegetated slope failure events following the heavy rains in mountains are getting higher and higher. In-depth researches of this problem have great practical significance for landslide susceptibility assessment. Up to now, the existing research achievements of landslides induced by rainfall mainly focused on the interrelation between rainfall events and landslide events which no direct relation, as well as the aspects of water-rock interaction in rock-soil mass of slope. But the response process and response mechanism of groundwater to rainfall has received much less attention. The response of soil water to rainfall is the first step of the response of groundwater to rainfall. It is widely recognized that this response process in soils are strongly determined by soil structure. There are various macropores in vadose zone soils of well vegetated natural slope. However, a lot of research work has not been considered the influence of macropores on rainfall infiltration in slope. So, the research of rainfall infiltration in well vegetated slope is the bottleneck of systematically understanding the response of groundwater to rainfall. The effects of macropores on rainfall infiltration in vadose zone soils of well vegetated slope are studied by methylene blue dye tracer infiltration experiment, iodine-starch visual method, theoretical analysis and HYDRUS-2D finite element software numerical simulation method. The main research achievements are summarized as the following:1、The physical-chemical-hydraulical properties of unsaturated soil in well vegetated slope were investigated by laboratory test and field test in Chenggong experimental plots and in Touzhai experimental plots. The test results show that the water content, total porosity, organic matter, storativity of free water and the saturated hydraulic conductivity of soil in well vegetated slope are larger than the bare slope and the cultivated soils:on the contrary, the soil specific gravity and the bulk density are smaller in well vegetated slope. The storativity of free water and the saturated hydraulic conductivity decreased with increasing soil depth.2、In order to distinguish the types of macropores, the distribution patterns of macropore flow paths and the effects of root systems, organic matter, gravel and soil fauna on the distribution patterns of macropore flow paths. Methylene blue was chosen as the dye tracer. Dye tracer infiltration experiments were conducted in well vegetated slope. Results show that:Root channels (including with bark, without bark and root-soil interstice), animal burrows, inter aggregate porosity and gravel-soil interstice are common macropores in well vegetated slope. Root systems have significant effects on the quantity, the scale and the distribution patterns of macropore flow paths, especially, those which had developed vertically or in a downslope direction. The organic matter was favorable for the formation of the inter-aggregate pore. Gravel is favorable for the formation of macropore flow paths, especially in the topsoils. The effects of soil fauna on the morphology of animal burrows network are related to the life inbit of soil animals, soil texture and root distribution.3、Iodine-starch visual method and cluster analysis were used to study the distribution pattern of water flow paths in well vegetated slope. Research indicated that the heterogeneity of the distribution pattern of water flow paths increased with decreasing soil depth under intense rainfall condition. The heterogeneity of water flow paths in the direction of downslope is more significant than in the direction of vertical.4、The theory of soil water movement studies indicate that the research of unsaturated soil water movement has gone through two leaps. The existing research achievements of macropore flow model mainly focused on the agricultural soil, which are unfit for researching on the macropore flow in well vegetated slope. The conception mode of root-soil interstice macropore flow in well vegetated slope are presented.5、Base on the results of dye tracer infiltration experiments, water flow paths tracer experiments and the relative existing research outcomes, the effects of macropores on rainfall infiltration in well vegetated slope were discussed. We come to the following conclusions: Macropore flow in vadose zone of well vegetated slope is initiated through macropores intercept subsurface storm flow. Macropore flow lead to the fast rise in the infiltration and speed up rainfall infiltration. Stem flow can reach the deep soil quickly. The saturated hydraulic conductivity of the animal burrows and the soil are correlated positively with the biomass, total area, length and volume of animal burrows. Gravel-soil interstice intercept subsurface storm flow and other macropore flow, and increase the infiltration capacity of soils. The effect of root channel on rainfall infiltration is far greater than from animal burrows. The heterogeneity of macropore network system leads to ununiformity of the distribution of soil water content.6、Making use of the finite element program of HYDRUS-2D, the influence of macropore and the diameter, the length, the tortuosity, the density and the orientation of macropores were simulated under same rainfall process. The result indicates:macropore accelerate the rainfall infiltration and weaken the subsurface flow, and delay the time of appearance of transient state saturated zone, and then lend to the shape of wetting front is irregular. The influence of the diameter of single macropore to the distribution of the soil water content and the pressure head, the shape of wetting front are not obvious. The increasing of macropore diameter lead to the velocity of preferential flow decreases, the decay of the time of ponding in macropores and the ponding fast discharge. The increasing of the length of macropore lead to the shape of wetting front is more irregular, the depth of infiltration increases, the decay of the time of ponding in macropores and the ponding depth of macropore increases. The velocity of preferential flow is less influenced by the length of macropore. The decay of the time of ponding in macropores and the velocity of preferential flow begin to increase and then decease with the increasing of the tortuosity of macropore. The depth of rainfall infiltration decreases and the ponding depth of macropore increases with the increasing of the tortuosity of macropore. The tortuosity of macropore effects on the shape of wetting front are more important at the start of the infiltration than at later times. The irregularitiy of the shape of wetting front decreases with the increasing of the tortuosity of macropore. Because of the increasing of the density of macropore, the complex of shape of wetting front and getting more and more. The penetration rate of rainfall increases with the increasing of the density of macropore. The increasing of density of macropore lead to the interaction between differential macropore getting more and more pronounced. The irregularitiy of the shape of wetting front decreases with the decreasing of the angle between the orientation of macropore and the trend of the slope. The velocity of preferential flow increases with the decreasing of the angle. Macropore that in the topsoil and parallel to slope surface leads to an even lower infiltration rate of precipitation.更多还原