MECHANISM OF FORMATION OF FREEZE-THAW LOESS LANDSLIDES IN ILI REGION
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摘要: 伊犁地区属典型季节性冻土区,冻融黄土滑坡发育强烈,对人民生命财产安全造成巨大隐患。本文以伊宁县喀拉亚尕奇乡冻融黄土滑坡作为研究对象,采用现场实地调查、原位地温监测、室内试验和数值模拟方法等手段,开展冻融黄土滑坡形成机理研究。通过分析研究区内冻融黄土滑坡的发育特征及影响因素,证实了黄土滑坡表层土体受冻融循环作用的长期影响,并且将研究区内的季节冻融循环总结为未冻期、交替冻结期、冻结期、融解期4个阶段。结果表明,原状黄土的黏聚力受冻融循环次数的影响较大,在冻融循环4次时降低幅度达到最大,最后黏聚力有趋于水平的趋势;随着冻融循环次数的加大,内摩擦角呈现下降的趋势,但下降幅度较小,影响的度数为3°~5°。模拟结果显示冻融黄土滑坡的冻结滞水效应显著,冻结期由于冻结层强度较大,滑坡稳定性不降反增,初始融化阶段,斜坡稳定性骤降,处于整个冻融过程中最不稳定阶段。研究表明冻融黄土滑坡的形成受冻融循环作用和冻结滞水作用的双重影响。Abstract: Ili region is a typical seasonal permafrost area. The development of freeze-thaw loess landslides is strong,causing great potential danger to the safety of people's lives and properties. In this paper,we take the frozen-thawed loess landslide in Karaya Gaqi Township,Yining County,as the research object,and use the means of on-site field investigation,in-situ ground temperature monitoring,indoor experiment and numerical simulation method to carry out the research on the formation mechanism of frozen-thawed loess landslide. By analyzing the developmental characteristics and influencing factors of freeze-thaw loess landslides in the study area,it is confirmed that the top soil layer of loess landslides is subject to the long-term influence of freeze-thaw cycle action,and the seasonal freeze-thaw cycle in the study area is summarized into four stages: unfrozen period,alternating freezing period,freezing period,and thawing period. The test results show that the cohesion of the original loess is greatly affected by the number of freeze-thaw cycles,and the decrease reaches the maximum at 4 times of freeze-thaw cycles,and finally the cohesion has a tendency to level off. With the increase of the number of freeze-thaw cycles,the angle of internal friction shows a tendency to decrease,but the decrease is small,and the influence of the degree is in the range of 3°~5°. The simulation results show that the freezing hysteresis effect of freeze-thaw loess landslides is significant,and the stability of landslides increases instead of decreasing during the freezing period due to the greater strength of the frozen layer,and the stability of the slopes decreases abruptly when the initial thawing stage is at the most unstable stage in the whole freeze-thaw process. The study shows that the formation of freeze-thaw loess landslide is affected by both freeze-thaw cycle and freezing hysteresis.
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图 9 冻融过程中地下水渗流场与X向位移场变化
a. 初始渗流场;b. 冻结30d后渗流场;c. 融化30d后渗流场;d. 冻结水位雍高幅度与距地下水溢出带水平距离关系图;e. 初始X向位移场;f. 冻结30d后X向位移场;g. 初始融化时X向位移场;h. 融化30d后X向位移场
Figure 9. Changes in groundwater seepage field and X-directional displacement field during freeze-thaw:(a) initial seepage field; (b) seepage field after 30d of freezing; (c) seepage field after 30d of thawing; (d) plot of the magnitude of the Yong height of the freezing water table versus the horizontal distance from the groundwater overflow zone; (e) initial X-direction displacement field; (f) X-direction displacement field after 30d of freezing; (g) X-direction displacement field at the time of the initial thawing;(h) X-direction displacement field after 30d of thawing
表 1 喀拉亚尕奇乡黄土的物理性质指标
Table 1. Indicators of physical properties of loess in Karaia Gaqi Township
编号 天然含水率
ω0/%比重
Gs天然密度
ρ0/g·cm-3干密度
ρd/g·cm-3液限
ωL/%塑限
ωP/%1 11.6 2.69 1.42 1.27 25.3 20.1 2 10.5 2.69 1.48 1.34 25.8 20.1 3 6.4 2.71 1.43 1.35 31.4 21.5 表 2 各岩土体的物理力学参数
Table 2. Physical and mechanical parameters of each geotechnical body
材料 重度/kN·m-3 黏聚力/kPa 内摩擦角/(°) 弹性模量/MPa 泊松比 渗透系数/m·s-1 天然黄土 14.5 31.0 28.9 18.3 0.34 9.36×10-7 饱和黄土 19.9 5.3 20.6 8.5 0.50 2.78×10-6 冻土 20.5 1480.0 10.3 200.0 0.25 9.36×10-8 冻融循环土 18.0 10.2 25.4 11.6 0.38 4.58×10-6 -
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