Seepage Characteristics and Stability Analysis of Wanzhou Shilongmen Landslide Under the Combined Effect of Rainfall and Reservoir Water
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摘要:
三峡库区库岸堆积层滑坡广泛发育,其稳定性主要受降雨和库水位变动联合作用影响。本文以重庆市万州区石龙门堆积层滑坡为例,建立精细地质模型,采用有限元方法对该滑坡开展了数值模拟研究,探讨其变形与稳定性的变化特征,总结在降雨和库水位联合作用下堆积层滑坡的渗流响应规律。结果表明:降雨和库水位下降是滑坡的关键诱因,降雨会提升滑坡中后部地下水位,当降雨强度超出土体入渗能力后,新增降雨多以坡面径流排泄,而库水位变动影响前缘地下水位及孔隙水压力。在库水位下降联合降雨作用下,滑坡内部应力-应变及稳定性显著恶化,渗流与水力梯度的增强加剧了滑坡不稳定性。本文研究可为堆积层滑坡的变形机制分析及监测预警提供参考。
Abstract:In the Three Gorges Reservoir area, piling layer landslides on the bank of the reservoir are widely developed, and their stability is mainly affected by the combined effect of rainfall and reservoir water level change. This paper takes Wanzhou Shilongmen piling layer landslide as an example, establishes a refined geological model, and carries out numerical simulation research on the landslide using the finite element method, to study the characteristics of the change of its deformation and stability, and to explore the seepage response law of the piling layer landslide under the combined effect of rainfall and reservoir level. The results show that: rainfall and reservoir level decline are the key triggers of landslides, rainfall will raise the groundwater level in the middle and back of landslides, and when the intensity of rainfall exceeds the infiltration capacity of the soil body, the additional rainfall is mostly discharged as slope runoff. The change of the reservoir level affects the groundwater level and pore water pressure at the leading edge. Under the combined effect of the reservoir water level drop and rainfall, the internal stress-strain and stability of the landslide deteriorate significantly, and the enhancement of seepage and hydraulic gradient aggravates the landslide instability. This paper provides a useful reference for analyzing the deformation mechanism and monitoring and early warning of landslides in the accumulation layer.
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表 1 滑坡岩土体参数取值
Table 1. Parameter value of landslide rock and soil mass
位置 重度(kN·m−3) 弹性模量(Mpa) 泊松比 内摩擦角c(°) 粘聚力 $ \mathit{\varphi } $ (kpa)天然 饱和 天然 饱和 滑体 20.1 20 0.3 15.2 13.5 38 29 滑床 30 16000 0.4 38.2 1120 滑带 21.0 10 0.2 12.9 8.7 27 22 表 2 万州区降雨重现期统计表
Table 2. Statistics of rainfall return period in Wanzhou
重现期(a) 5 10 20 50 100 降雨极值(mm) 168.5 199.8 253.2 281.4 320.1 平均降雨强度(mm/d) 56.2 66.6 84.4 93.8 106.7 表 3 石龙门滑坡数值模拟工况设计
Table 3. Design of numerical simulation conditions for Shilongmen landslide
工况分类 工况编号 工况条件 模拟时间(d) 降雨 工况1 库水位145 m+50年一遇暴雨 10 工况2 库水位145 m+100年一遇暴雨 10 库水位升降 工况3 库水位从145 m上升到175 m 75 工况4 库水位从175 m下降到145 m 170 库水位下降
叠加降雨工况5 库水位从175 m下降到145 m+50年一遇暴雨 170 工况6 库水位从175 m以3 m/d下降速度下降至145 m+100年一遇暴雨(极端条件) 10 表 4 石龙门滑坡稳定性系数变化统计表
Table 4. Statistical table of changes in stability coefficients of the Shilongmen landslide
工况条件 工况编号 稳定性系数 变幅(%) 初始值 最小值 最终值 静止水位+暴雨 工况1 1.202 1.065 1.181 11.4 工况2 1.202 1.059 1.137 11.9 水位涨落 工况3 1.202 1.202 1.227 2.1 工况4 1.271 1.257 1.257 1.0 库水位下降+降雨 工况5 1.271 1.028 1.028 19.1 工况6 1.271 0.932 0.932 26.6 -
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