Failure Mechanism of Thick Colluvium Landslide Triggered by Heavy Rainfall Based on Model Test
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摘要: 降雨触发滑坡机制是开展滑坡灾害气象预警、风险评价和工程治理的关键科学问题.选择三峡库区巴东燕子滑坡作为典型实例，设计制作滑坡物理模型，通过设置3种强降雨工况，实时监测滑坡不同位置土压力、孔隙水压力和含水率数据，结合数值模拟与堆积层滑坡动力学理论分析，探讨了厚层堆积层滑坡在强降雨条件下的变形特征与破坏机制.试验表明：强降雨条件下滑坡变形始发于坡体上部地形转折处的后缘裂隙；强降雨导致滑坡内部土压力、孔隙水压力和含水率不同程度上升，且滑带处的上升幅度明显大于滑坡浅表处；100 mm/h极端降雨结束后，滑坡开始缓慢蠕滑，随后经历加速、短暂减速、再次加速下滑直至滑移停止的破坏演化过程.滑坡触发机制为：降雨初期，坡表以孔隙流入渗为主，后缘裂隙的形成构成了雨水入渗的优势渗流通道，雨水入渗造成滑坡地下水位上升，坡脚冲刷垮塌导致滑坡前缘出现渗流排泄点，产生动水压力，同时滑带在长时间浸泡软化作用下强度持续降低.滑坡最终在滑带剪切破坏下发生了整体推移式滑动.Abstract: The mechanism of rainfall-triggered landslides is a key issue for the development of meteorological warning, risk assessment and engineering treatment of landslide disasters. In this paper, the Badong Yanzi landslide in the Three Gorges Reservoir area was selected as a typical example, and the physical model of the landslide was designed and produced. By setting three heavy rainfall conditions, the soil pressure, pore water pressure and moisture content data at different positions of the landslide can be monitored at all times. According to the test results, combined with the dynamic theory of colluvium landslide and numerical simulation analysis, the deformation characteristics and failure mechanism of thick colluvium landslide under heavy rainfall conditions were discussed. Test results show that under the condition of heavy rainfall, the deformation of the landslide started from the topographic turning point at the trailing edge of the slope. Heavy rainfall caused the soil pressure, pore pressure and moisture content data inside the landslide to rise to varying degrees, and the rise in the slip zone was significantly greater than the shallow surface of the landslide; after the extreme rainfall of 100 mm/h, the landslide began to creep slowly and then underwent a failure evolution process of acceleration, short deceleration, and acceleration again until the destruction process stopped. The trigger mechanism of the landslide is analyzed as follows. In the early stage of rainfall, the slope surface is dominated by pore infiltration, and the formation of rear edge fissures has become the dominant seepage channel for rainwater infiltration. The infiltration of rainwater causes the groundwater level of the slope to rise, the hydrostatic pressure of the fissure at the trailing edge of the landslide increases, and the erosion and collapse of the slope toe leads to seepage drainage points on the front edge of the landslide, resulting in hydrodynamic pressure. And the strength of the sliding belt continues to decrease under the effect of long-term soaking and softening. The landslide eventually undergoes overall slippage caused by shifting under the shear failure of the sliding zone.
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Key words:
- colluvium landslide /
- heavy rainfall /
- model test /
- numerical simulation /
- failure mechanism /
- engineering geology
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图 1 燕子滑坡主滑方向剖面图
Fig. 1. Section view of the main sliding direction of the Badong Yanzi landslide
图 2 三峡库区堆积层滑坡统计结果
Fig. 2. Statistical results of accumulation landslides in the Three Gorges Reservoir area
图 6 滑坡宏观变形过程
a.工况一试验开始；b.工况一降雨20 min；c.工况一降雨3 h；d.工况一静置2 h；e.工况二降雨1 h；f.工况二降雨3.5 h；g.工况三降雨1 h；h.工况三停雨15 min
Fig. 6. Deformation process of model landslide
图 7 滑坡破坏过程位移曲线
a.蠕滑阶段；b.第1次加速下滑；c.短暂减速；d.再次加速直至坡面平缓停止
Fig. 7. Displacement curve of landslide failure
图 8 滑坡整体下滑过程
a.蠕滑阶段；b.加速阶段；c.后缘滑带地下水；d.滑带擦痕；e.滑坡前缘堆积；f.后缘裂缝剖面
Fig. 8. Sliding down process of landslide model
图 9 滑坡含水率变化监测曲线
a.工况一；b.工况二；c.静置阶段；d.工况三
Fig. 9. Curves of moisture content of landslide
表 1 原型滑坡及相似材料部分参数对照
Table 1. Comparison of some parameters of Yanzi landslide and model landslide
滑坡结构设计 密度ρ
(g·cm-3)粘聚力c
(kPa)内摩擦角φ
(°)渗透系数k
(cm·s-1)坡体 原型坡体 1.76 25.8 23.8 3.66×10-4 配制坡体 1.80 5.6 23.0 1.15×10-5 配制方案 原状土∶河砂∶碎石∶膨润土∶水=10∶8∶2∶3∶4 滑带 原型滑带 1.95 4.67 21.3 \\ 配制滑带 1.89 0.50 22.0 \\ 配制方案 膨润土∶玻璃珠∶水=3∶3∶1 滑床 制作方案 砖砌基岩 
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表 2 降雨工况设置
Table 2. Setting of rainfall conditions
降雨工况 模拟实际雨强（mm/h） 观测时长（h） 工况一 50 降雨4 h，停2 h 工况二 75 降雨4 h，停2 h 工况三 100 降雨4 h，停2 h 注：工况二观测结束后静置36 h开始工况三.
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