【摘要】：多年凍土是青藏高原自然生態(tài)系統(tǒng)重要的組成部分。隨著氣候變暖以及青藏高原各類工程活動的影響下,多年凍土在不斷退化,由此引發(fā)的熱融滑塌是多年凍土區(qū)典型的熱融災(zāi)害之一。熱融滑塌加劇土壤凍融侵蝕,不僅造成坡地坍塌后退,使得凍土區(qū)修筑工程構(gòu)筑物面臨危險,而且改變活動層的水熱過程,使得多年凍土失去恢復(fù)能力并導(dǎo)致區(qū)域生態(tài)系統(tǒng)惡化。本文以可可西里地區(qū)出現(xiàn)初始發(fā)展階段的小型熱融滑塌為研究對象,通過現(xiàn)場監(jiān)測、土壤性質(zhì)分析、溫度水分分析、穩(wěn)定性分析,結(jié)合分形理論與無限邊坡理論,開展了青藏高原多年凍土區(qū)熱融滑塌對土壤凍融侵蝕的研究,得出以下主要成果:(1)通過2013-2016年對熱融滑塌坡面變形的監(jiān)測表明,失穩(wěn)坡面不是一次性整體滑落形成的,而是每年發(fā)生的熱融沉降使得后緣坡體融化、開裂,失穩(wěn)的活動層融土在融化季節(jié)成流塑態(tài)沿著滑動面向下緩緩蠕動下滑,從而逐漸改變了研究區(qū)的地形地貌。鉆孔試驗表明,熱融滑塌土壤的凍融侵蝕主要發(fā)生在0~40cm深的表層土壤中,最大不超過50 cm。失穩(wěn)坡面土壤凍融侵蝕的強度明顯大于坡頂未受影響區(qū)的原狀土壤。(2)熱融滑塌的凍融侵蝕導(dǎo)致著土壤性質(zhì)發(fā)生明顯的變化。隨著熱融滑塌的發(fā)展,地表植被遭到破壞,活動層表層土壤粗�；�、均質(zhì)化,容重沿坡向逐漸增大,土壤細顆粒和有機質(zhì)先在泥流緩坡30-40cm土層中大量沉積,隨后在坡底大量流失。地下冰的融化釋放的大量融化水導(dǎo)致失穩(wěn)坡面土壤水分顯著增加并使得土體抗剪強度顯著降低。(3)應(yīng)用無限邊坡理論對熱融滑塌坡面的穩(wěn)定性分析可知,在融化季節(jié),后緣坎壁的滑動不可避免,泥流緩坡區(qū)及坡底處于較穩(wěn)定的狀態(tài),蠕動位移輕微;在非融化季節(jié),整個坡面是穩(wěn)定的。這與現(xiàn)場觀測的結(jié)果基本一致。(4)熱融滑塌土壤的凍融侵蝕減弱了活動層對熱量傳輸?shù)木彌_作用,擴大了下伏多年凍土的消融。坡面監(jiān)測系統(tǒng)顯示研究樣地后緣坎壁變得越來越陡而坡面前緣正在形成一個大凹地,而多年凍土消融的擴大,大量的融水向活動層釋放,泥流緩坡出現(xiàn)漫流,坡底出現(xiàn)積水洼地。結(jié)合熱融滑塌與熱融湖塘不同影響跡地以及湖岸坡地的活動層變化規(guī)律的相似性,本文預(yù)測坡面前緣會形成一個熱融湖塘,而整個研究樣地會形成熱融湖塘毗鄰湖岸熱融滑塌的地貌。
[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.
【學位授予單位】：蘭州大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P642.14

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