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MECHANISM OF SURFACE WATER INFILTRATION INDUCED DEEP LOESS LANDSLIDE
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摘要: 在黄土地区，雨后观测和人工降雨试验均表明地表水在黄土中的入渗深度有限，并不影响黄土深部的含水率。因此水分入渗是否直接造成斜坡深层滑移颇受争议。本文通过黄土地区自然降雨条件下的现场观测，发现地表水在黄土中的入渗沿垂直剖面可以划分为3个带：即活动带，稳定带和饱和带。活动带受大气降雨和蒸发的影响，为瞬态流，向下则转化为稳定流；稳定带含水率不变，但仍有稳定的水分运移至地下水位。地下水以下降泉的形式排泄。在入渗和排泄条件长期不变的情况下，地下水位可维持动态平衡。若地表入渗量加大，如灌溉或管道漏水等，稳定带含水率升高，并伴随地下水位抬升，以达到新的平衡，此水文动态转化过程会诱发滑坡。以延炼滑坡为例，分析了长期地表水间歇性滴渗条件下，边坡的水力动态变化过程，及其对边坡稳定性的影响。观测及分析结果表明，黄土深层滑坡主要与地表水入渗导致的地下水位抬升有关，由于其过程缓慢，容易被忽视而致灾。Abstract: In loess area, both artificial rainfall field test and in-situ observation under natural rainfall conditions suggest that the influence of surface water is limited to the top several meters, below which the variation of soil water content is little. Therefore, it is a controversy to fact that the surface water infiltration can induce loess landslides with deep seated failure surfaces. In this study, an in-situ observation test is undertaken in a thick loess layer for a period of one year from June 1st, 2015 to May 31st, 2016. Results show that water infiltration in the loess can be divided into three zones, namely, active, stable, and saturated zones. The active zone is influenced significantly by precipitation and evaporation events, where water flow is a transient behavior. The stable zone is characterized with a stable water content and steady seepage flow. The saturated zone is where groundwater exits, which can be drained in the forms of spring. In the long run, the hydraulic condition reaches an equilibrium state with a stable water content in the stable zone and stable ground water table level. However, this equilibrium state can be disturbed with a higher surface water infiltration, for example irrigation water and leakage from pipelines, which contributes to a new equilibrium state with higher stable water content in stable zone and higher GWT level. Loess landslides with deep seated failure surfaces may occur during the transitional process from the initial equilibrium state to the new equilibrium state. Yanlian deep loess landslide is taken as an example to illustrate the mechanism of surface water infiltration induced deep landslides. The hydraulic response to long-term surface drop water and its influence to slope stability are analyzed. Results highlight the close relationship between deep loess landslides and long-term surface water infiltration, which is easy to be neglected due to its slow flow rate.
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Key words:
- Unsaturated loess /
- Water infiltration /
- Steady zone /
- Deep loess landslide
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图 2 降雨量、气温、气压和2 m以上水分监测和模拟结果
Figure 2. The monitoring results of precipitation, air temperature and air pressure as well as the monitoring and simulating soil water content above 2 m depth
图 3 2 m以下土体水分监测和模拟结果及地下水位监测结果
Figure 3. The soil water contents of monitoring and simulating below 2 m and the underground water level of monitoring
图 6 监测含水率与模拟含水率沿剖面的变化范围及分带
Figure 6. Variation span of monitoring and simulating soil water content on the profile and zonation
图 10 边坡稳定系数随水入渗时间的变化
Figure 10. Variation of the safety factors with the surface water infiltration duration
表 1 模型主要参数
Table 1. Parameters used in the numerical modeling studies
地层 SWCC ks/m·d-1 Q3 a=9.7，m=1.808，n=1.0 0.110 Q2 a=29.7，m=0.922，n=2.4 0.044 Q1 a=8718，m=0.825，n=96.5 0.027 
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