扰动堆积土体边坡土壤侵蚀动力过程试验研究

发布时间：2018-03-27 18:44

本文选题：黄土高原　切入点：扰动堆积土体　出处：《中国科学院研究生院（教育部水土保持与生态环境研究中心）》2014年硕士论文

【摘要】：随着西部大开发的推进和区域经济建设的需求，黄土高原地区生产、开发类建设项目越来越多，由此引起的扰动堆积土体所带来的土壤侵蚀问题愈发凸显。由于遭到剧烈的扰动，松散堆积土体原有土体结构遭到破坏，并且常常缺乏水土保持工程措施和植物措施的保护，在暴雨条件下极易发生剧烈土壤侵蚀而破坏农田、道路等，给人民的生命财产带来巨大的损失。为了探明扰动堆积土体的土壤侵蚀特性随坡度和初始水动力条件的变化，我们建设了标准的试验小区，探讨其在3个坡度、4个放水流量下土壤侵蚀的特性及其发生的原因和过程。通过整个试验过程得到以下主要结论：（1）从小区的土壤侵蚀特性来看：试验条件下的产流速率随时间的变化规律基本一致，均呈现先增大然后基本稳定的变化特性；平均产流速率与放水流量呈线性正相关关系；在30L/min的放水流量下产流总量与坡度没有明显关系，其他流量下产流总量随着坡度的增大而增大。小区产沙速率随时间的变化规律在不同坡度不同放水流量并不完全一致，基本呈现以下2种变化规律：①在最大放水流量下，产沙速率先迅速增大，然后逐渐减小，最后稳定在一定的范围内；②在其他情况下，产沙速率先增大然后基本稳定。平均产沙速率与放水流量、坡度均存在线性正相关关系，但Ma-Q回归方程的显著性水平（Sig.值）要高于Ma-S回归方程的显著性水平，说明与坡度相比放水流量对平均产沙速率的影响更大。（2）径流含沙量随时间的变化规律主要一下有3种：①放水流量较小且坡度较小时，径流含沙量在较长的一段时间内基本稳定，在试验后期（18min）才逐渐减小；②放水流量较大或坡度较大时，径流含沙量前期（9～12min以前）逐渐减小之后基本稳定；③介于前两种情况之间的径流含沙量随时间不断减小。平均径流含沙量与放水流量呈线性负相关关系，与坡度则呈线性正相关关系。试验条件下产流产沙关系基本可以用幂函数y=axb来表达，a值在0.388～1.445之间变化，b值在0.256～0.911之间变化；随着放水流量和坡度的增大a值在不断增大，而b值在不断减小；当放水流量为60L/min时，虽然产流产沙之间仍呈现正相关关系，但幂函数已经不能很好地拟合两者之间的关系。（3）各个放水流量下，在小区中部（断面3上下）都存在一个流速大小稳定在0.3～0.5m/s的断面。处在该断面以上的断面，平均流速随放水时间整体呈现减小趋势；处在该断面以下的断面，平均流速随放水时间整体呈现增大趋势。各观测断面的平均水深均随着放水时间的延长不断增加；在小区的上部（断面1～2）平均水深变化剧烈，而在小区中下部（断面3～5）平均水深变化较为舒缓并一直处在0.5mm～1mm之间；平均水深与放水流量无较为明显的关系。（4）试验条件下坡面流基本为层流，只有在断面1和部分时段为过渡流；除了个别现象外，坡面流均属急流范畴；各个放水流量下弗汝德数与雷诺数均为负相关关系；阻力系数与雷诺数存在幂函数关系，但与放水流量关系不明显。分析阻力系数沿坡长的变化情况发现，0～6m的坡长范围内土壤侵蚀强烈，是坡面流中泥沙的主要供给部位；6～20m坡长范围内土壤侵蚀微弱，该区域对坡面流中的泥沙仍有供给，但供给速率缓慢。坡面阻力系数与水深呈线性正相关关系，因此变化特性与水深基本一致。（5）水流切应力随坡长的变化可以很好地解释小区土壤侵蚀的主要发生部位在小区中上部（0～10m）的原因。水流切应力虽然与单位面积土壤侵蚀速率存在较好的线性关系，，但由于水流剪切力只代表了水流剥蚀土壤颗粒进入坡面流的能力，且本试验选取的坡度属于陡坡范畴，重力侵蚀作用表现强烈，该侵蚀模型已经不适合来解释本试验条件下侵蚀速率的变化。由于水流功率是反映了坡面流搬运能力，所以水流功率模型能运用于本试验条件下来反应土壤侵蚀速率的变化。
[Abstract]:With the advance of western development and regional economic construction demand and production in the Loess Plateau, the development of construction projects more and more, the disturbance caused by the accumulation of soil erosion on soil caused by the increasingly prominent. Due to severe disturbance, loose accumulation soil the original soil structure destroyed, and often lack of protection measures and maintain engineering plant measures of soil and water, severe soil erosion and destruction of farmland, prone to storm conditions such as roads, bring huge losses to people's lives and property. In order to explore changes of soil erosion characteristics of soil disturbance accumulation with slope and initial hydrodynamic conditions, we establish a standard test area, on the 3 4 slope, soil erosion characteristics of the water flow and its causes and process. The main conclusions are as follows through the whole test process:
(1) from the area of the soil erosion characteristics: test conditions of runoff rate variation with time is consistent, increased first and then change characteristics is basically stable; average runoff rate showed a linear correlation with the flow discharge and slope flow in total; no obvious relationship between the discharge of 30L/min production and other traffic flow volume increased with the increase of slope area. The sediment rate changes with time at different slope of different discharge is not entirely consistent, characterized by the following 2 basic changes: in the maximum discharge, sediment yield rate first increases rapidly, then decreases gradually, finally stabilized in a certain range; in other cases, the sediment yield rate increases at first and then remained stable. The average sediment discharge rate, there was a positive linear correlation between the slope, but the regression equation was Ma-Q The Sig. value is higher than the significant level of the Ma-S regression equation, indicating that the effect of the discharge flow rate on the average sediment yield is greater than that of the slope.
(2) the variation of runoff sediment concentration with time mainly has 3 kinds: first, the water flow is small and the slope is small, the basic stability of the sediment concentration in a longer period of time, at the end of the experiment (18min) was gradually decreased; the water flow is larger and larger slope, runoff sediment early (9 ~ 12min ago) decreased gradually after basically stable; sediment concentration between the range of the first two cases with time decreases. The average sediment concentration of runoff and discharge showed a linear negative correlation, linear positive correlation with slope. The experimental conditions of runoff and sediment relationship with power function to express y=axb and the a value is between 0.388 ~ 1.445, the b value is between 0.256 ~ 0.911; with the flow discharge and slope increased a value increasing, while the b value decreases; when the water flow is 60L/min, while the runoff and sediment There is still a positive correlation between the two, but the power function can not well fit the relationship between the two.
(3) the water flow rate, in the central area (Section 3) there is a stable flow in the 0.3 ~ 0.5m/s section. In the section above the section, with the overall average velocity of drainage time decreased; in the following section of the section, the average flow velocity with the drainage time showed an increasing trend. The average depth of each observation section increased with the increase of discharge time; in the area of the upper part (section 1~2) with an average depth of change, and in the area in the lower part (section 3~5) with an average depth of change is soothing and has been in the 0.5mm ~ 1mm; the average depth of water flow and no obvious relationship.
(4) the test conditions of overland flow is laminar, only in Section 1 and part time for transition flow; in addition to the individual phenomenon, overland flow is jet flow discharge under each category; Froude number and Reynolds number were negatively correlated; the relationship between the power function of drag coefficient and Reynolds number, but the relationship and the water flow is not obvious. Analysis of resistance coefficient changes along the slope length, slope length of 0 ~ 6m within the scope of intense soil erosion is the main supply of overland flow sediment in the area; 6 ~ 20m slope length range of soil erosion in the region is still weak, the supply of sediment in runoff, but supply the rate of slow slope. The drag coefficient increases linearly with the depth, the change characteristics and depth are basically the same.
(5) the flow shear stress varies with the length of the slope can be well explained by the area of soil erosion mainly occurred in the area of the upper part (0 ~ 10m). The reason of flow shear stress and soil erosion rate per unit area, although there was a good linear relationship, but due to shear stress only on behalf of the soil the particles flow into the erosion of runoff, and the test of the slope slope belongs to the category of the strong performance of the role of gravity erosion, erosion model is not suitable to explain changes in erosion rates under the conditions of this experiment. Because the flow power reflects the transport capacity of overland flow, so the water power model can be used in this experiment down reaction the soil erosion rate of change.

【学位授予单位】：中国科学院研究生院（教育部水土保持与生态环境研究中心）
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：S157.1

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