Analysis on the mechanism of bank slope sliding considering the effect of reservoir water fluctuation and sliding zone weakening
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摘要: 以三峡库区凉水井滑坡为研究对象，采用理论分析与数值模拟的研究手段，构建了滑带强度弱化模型，提出了渗流驱动的滑坡启滑判据，应用Geo-studio有限元程序分析了库水不同升降速率对滑坡稳定性的影响，揭示了库水升降作用下岸坡渗流场演变规律和渗流驱动下的启滑机制。研究表明：（1）渗透压力与渗透时间的变化是滑带土强度弱化的关键因素，弱化到临界强度时，在渗流驱动下发生压剪破坏而启滑，由局部向整体以渐进模式破坏失稳；（2）库水升降过程中，坡体内孔隙水压力滞后性较明显，水位升降速率会影响坡体地下水响应时程，升降速率越大，孔隙水压力变化越大，渗流驱动力越大，滑坡稳定性变化越快，越趋近于渐进破坏；（3）库水位从175 m降到145 m，凉水井滑坡滑面法向应力最大降低了38.19%，剪应力最大降低了22.20%，有效法向应力最大落差为168.64 kPa，抗剪强度最大落差为63.45 kPa。以上分析结论与规律可为涉水滑坡启滑机制分析、库岸山体滑坡失稳研究及应急防治工程等提供科学依据和理论方法。Abstract: This study focuses on the Liangshuijing landslide in the Three Gorges Reservoir area, using theoretical analysis and numerical simulations methods to construct a strength weakening model for the sliding zone and proposes a criterion for seepage-driven landslide initiation. The influence of different water level rise and fall rates on landslide stability is analyzed using the finite element program Geo-Studio, and the evolution laws of bank slope seepage field under the rise and fall of reservoir water and the starting and sliding mechanism caused by seepage are revealed. The research finds that changes in seepage pressure and time are crucial in weakening the strength of sliding zone soil. Once it reaches the critical strength, seepage causes pressure shear failure, leading to the initiation of the landslide, which progresses from local to overall failure. During the reservoir water level rise and fall process, the hysteresis of pore water pressure in the slope body is evident, and the rate of water level change affects the response time of groundwater in the slope. A faster rate of water level change leads to a greater change in pore water pressure, more driving force from seepage, and a faster change in landslide stability and a closer approach to progressive failure. When the reservoir water level drops from 175 m to 145 m, the normal stress on the sliding surface of the Liangshuijing landslide decreases by 38.19%, and the shear stress decreases by 22.20%. The maximum decrease in the effective normal stress is 168.64 kPa and the maximum decrease in shear strength is 63.45 kPa. The above findings provide a scientific basis and theoretical methods for the analysis of landslide initiation and sliding mechanisms, instability research of reservoir bank landslides, and emergency prevention and control engineering.
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图 1 渗流驱动的滑坡压剪破坏分析模型
Figure 1. Analysis model for seepage-driven landslides under pressure shear failure
图 3 凉水井滑坡典型地质剖面图
Figure 3. Typical geological cross-section of the Liangshuijing landslide
图 4 凉水井滑坡滑面形态特征
Figure 4. Morphological characteristics of the sliding surface of the Liangshuijing landslide
图 5 地表累积位移与时间的关系
Figure 5. The relationship between cumulative surface displacement and time
图 6 地表裂缝宽度累积与时间的关系
Figure 6. The relationship between cumulative surface crack width and time
图 7 凉水井滑坡稳定系数Fs-库水位（左）变化与滑带抗剪强度-库水位（右）变化
Figure 7. Stability coefficient Fs - change of reservoir water level (left) and shear strength of sliding zone - change of reservoir water level (right) of Liangshuijing landslide
图 8 滑带土抗剪参数反演
Figure 8. Inversion of shear resistance parameters for the sliding zone soil
图 9 渗流驱动力与库水位降落速度变化关系
Figure 9. The relationship between seepage driving force and falling rate of reservoir water level
图 10 凉水井滑坡启动及演化机制
Figure 10. Initiation and evolution mechanism of Liangshuijing landslide
图 11 凉水井滑坡渗流分析有限元模型
Figure 11. Finite element model for seepage analysis of Liangshuijing landslide
图 12 库水升降作用下凉水井滑坡地下水渗流场演变
Figure 12. Evolution of groundwater seepage field of Liangshuijing landslide under the action of reservoir water level rise and fall
图 13 库水升降作用下凉水井滑坡稳定性变化
Figure 13. Stability change of Liangshuijing landslide under the action of reservoir water level rise and fall
图 14 凉水井滑坡平均位移随降水时间变化
Figure 14. Variation of average displacement of Liangshuijing landslide with precipitation over time
图 15 降水条件下滑面法向力变化
Figure 15. Variation of normal force on sliding surface under precipitation conditions
图 16 降水条件下滑面剪力变化
Figure 16. Variation of shear force on sliding surface under precipitation conditions
图 17 库水升降条件下滑坡孔隙水压变化
Figure 17. Changes in pore water pressure of the landslide under reservoir water level rise and fall conditions
图 18 降水条件下滑面有效法应力与抗剪强度变化
Figure 18. Variation of effective normal stress and shear strength on sliding surface under precipitation conditions
表 1 滑坡计算参数一览表
Table 1. List of calculation parameters for Liangshuijing landslide
岩土体 弹性模量/GPa 泊松比 重度/（kN·m−3） 黏聚力/kPa 内摩擦角/（°） 天然 饱和 天然 饱和 天然 饱和 滑床 24 0.2 25.1 25.3 5650 5420 47.04 43.80 滑带 3 0.4 23.0 23.8 19.17 14.41 25.03 24.29 滑体 3 0.4 23.0 23.8 21.48 19.29 34.83 27.68 
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