青藏高原多年冻土区热融滑塌对土壤冻融侵蚀影响

发布时间：2018-10-12 14:32

【摘要】：多年冻土是青藏高原自然生态系统重要的组成部分。随着气候变暖以及青藏高原各类工程活动的影响下,多年冻土在不断退化,由此引发的热融滑塌是多年冻土区典型的热融灾害之一。热融滑塌加剧土壤冻融侵蚀,不仅造成坡地坍塌后退,使得冻土区修筑工程构筑物面临危险,而且改变活动层的水热过程,使得多年冻土失去恢复能力并导致区域生态系统恶化。本文以可可西里地区出现初始发展阶段的小型热融滑塌为研究对象,通过现场监测、土壤性质分析、温度水分分析、稳定性分析,结合分形理论与无限边坡理论,开展了青藏高原多年冻土区热融滑塌对土壤冻融侵蚀的研究,得出以下主要成果:(1)通过2013-2016年对热融滑塌坡面变形的监测表明,失稳坡面不是一次性整体滑落形成的,而是每年发生的热融沉降使得后缘坡体融化、开裂,失稳的活动层融土在融化季节成流塑态沿着滑动面向下缓缓蠕动下滑,从而逐渐改变了研究区的地形地貌。钻孔试验表明,热融滑塌土壤的冻融侵蚀主要发生在0~40cm深的表层土壤中,最大不超过50 cm。失稳坡面土壤冻融侵蚀的强度明显大于坡顶未受影响区的原状土壤。(2)热融滑塌的冻融侵蚀导致着土壤性质发生明显的变化。随着热融滑塌的发展,地表植被遭到破坏,活动层表层土壤粗粒化、均质化,容重沿坡向逐渐增大,土壤细颗粒和有机质先在泥流缓坡30-40cm土层中大量沉积,随后在坡底大量流失。地下冰的融化释放的大量融化水导致失稳坡面土壤水分显著增加并使得土体抗剪强度显著降低。(3)应用无限边坡理论对热融滑塌坡面的稳定性分析可知,在融化季节,后缘坎壁的滑动不可避免,泥流缓坡区及坡底处于较稳定的状态,蠕动位移轻微;在非融化季节,整个坡面是稳定的。这与现场观测的结果基本一致。(4)热融滑塌土壤的冻融侵蚀减弱了活动层对热量传输的缓冲作用,扩大了下伏多年冻土的消融。坡面监测系统显示研究样地后缘坎壁变得越来越陡而坡面前缘正在形成一个大凹地,而多年冻土消融的扩大,大量的融水向活动层释放,泥流缓坡出现漫流,坡底出现积水洼地。结合热融滑塌与热融湖塘不同影响迹地以及湖岸坡地的活动层变化规律的相似性,本文预测坡面前缘会形成一个热融湖塘,而整个研究样地会形成热融湖塘毗邻湖岸热融滑塌的地貌。
[Abstract]:Permafrost is an important part of natural ecosystem of Qinghai-Xizang Plateau. With the influence of climate warming and various engineering activities in the Qinghai-Tibet Plateau, permafrost is continuously degraded, and the resulting thermal thawing collapse is one of the typical thermal thawing disasters in permafrost regions. Thermal thawing contributes to soil freezing and thawing erosion, which not only causes slope collapse and retreat, makes the construction of engineering structures in permafrost region dangerous, but also changes the hydrothermal process of active layer. Loss of resilience of permafrost and deterioration of regional ecosystems. In this paper, the small thermal melt collapse in the initial development stage of Hohsili area is taken as the research object. Through field monitoring, soil property analysis, temperature and moisture analysis, stability analysis, combining fractal theory with infinite slope theory, In this paper, the research on soil freeze-thaw erosion caused by thermal thawing in permafrost region of Qinghai-Xizang Plateau has been carried out. The main results are as follows: (1) through monitoring the deformation of thermal thawing slope surface in 2013-2016, it is shown that the unstable slope surface is not formed by a one-off whole slide. It is the annual thermal melt settlement that causes the slope body to melt, crack, and destabilize in the melting season. The fluid-plastic state of the fluid-forming layer slides down the sliding direction, which gradually changes the topography and landform of the study area. The results of borehole test show that the freezing and thawing erosion of hot thawing soil occurs mainly in the surface soil of 0~40cm depth, with a maximum of less than 50 cm.. The intensity of soil freezing and thawing erosion on unstable slope is obviously higher than that of unaffected soil on the top of slope. (2) freezing and thawing erosion of hot thawing collapse results in obvious change of soil properties. With the development of thermal melt collapse, the surface vegetation was destroyed, the surface soil of active layer was coarse grained, homogenized, bulk density gradually increased along the slope, and the fine particles and organic matter were deposited in the 30-40cm soil layer of mudflow gentle slope firstly. Then there was a massive loss at the bottom of the slope. The large amount of melting water released by underground ice causes the increase of soil moisture and the decrease of soil shear strength. (3) the stability of hot melt landslide slope is analyzed by the infinite slope theory, and it is found that in the melting season, The slippage of the backside ridge wall is inevitable, the mudflow gentle slope area and the slope bottom are in a stable state, and the creeping displacement is slight, and the whole slope is stable in the non-melting season. This is consistent with the field observation results. (4) freezing and thawing erosion of thermal thawing soil weakens the buffer effect of active layer on heat transfer and expands the ablation of downhill permafrost. The slope monitoring system shows that the back edge of the sample land becomes steeper and steeper, while the front edge of the slope is forming a large concave, and the expansion of permafrost ablation, the release of a large amount of molten water to the active layer, and the spread of mudflow on the gentle slope. A stagnant depression appeared at the bottom of the slope. Based on the similarity between the thermal melt collapse and the different effects of the hot melt lake pond on the active layer of the sloping land and the slope land along the lake bank, this paper predicts that the front edge of the slope will form a hot melt lake pond. And the whole study will form the hot melt lake pond adjacent to the lake bank hot melt collapse geomorphology.
【学位授予单位】：兰州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P642.14

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