Analysis of failure modes and long-term stability of dangerous rock mass on typical karst bank slope in the Three Gorges Reservoir area
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摘要: 三峡库区地质环境复杂，受库水位升降作用影响岩溶岸坡消落区岩体劣化，加快了岸坡不稳定性发展。文章以三峡库区黄岩窝危岩体为研究对象，现场详查了消落带岩体劣化现象，计算了危岩体的长期稳定性数值。研究表明：黄岩窝危岩体存在垂直岩溶带和底部渗流带；底部渗流带处于消落带部位，存在软弱区和岩体劣化现象。考虑库水位和暴雨时岩溶水压岸坡稳定性系数为1.69，危岩体处于稳定状态。随着岩体劣化导致底部软弱区岩体参数不断下降，稳定性系数年均下降约0.01。预测在约57个周期性水位变动之后黄岩窝危岩体变为欠稳定状态，62个周期后发生失稳破坏。危岩体的破坏模式是顶部出现岩块倾倒崩落和底部软弱区贯通之后发生滑移的复合式破坏，与野外调查定性认识基本一致。研究结果对库区类似的地质灾害预警和防治有着重要的指导意义。Abstract: The Three Gorges Reservoir area presents a complex geological environment, where the deterioration of rock masses in the riparian zone of karst bank slopes is expedited by the fluctuating reservoir water levels of the reservoir, thereby hastening the evolution of the bank slopes towards instability. This study focuses on the Huangyanwo dangerous rock mass in the Three Gorges Reservoir area. A comprehensive filed investigation was conducted to scrutinize the deterioration phenomenon of rock masses within the water–level fluctuation zone, and a numerical analysis was performed to assess the long–term stability of the dangerous rock mass. The findings reveal the presence of a vertical karst zone and a bottom seepage zone in the Huangyanwo dangerous rock mass. The bottom seepage zone is situated within the water–level–fluctuation zone, characterized by areas of weakness and rock mass deterioration. Considering the influence of reservoir water levels and rainfall events, the stability coefficient of karst water pressure on the bank slope is calculated to be 1.69, indicating that the dangerous rock mass remains stable. Nevertheless, due to the progressive deterioration of rock mass parameters within the weak area at the bottom, the stability coefficient experiences an annual decline of approximately 0.01. It is predicted that the Huangyanwo dangerous rock mass will transition to an unstable state after approximately 57 cycles of periodic water level variations, and the instability failure will occur after 62 cycles. The failure mode of the dangerous rock mass involves a compound failure mechanism of toppling and sliding subsequent to the connection of the weak zone at the bottom, aligning closely with the qualitative understanding grained from field investigations. The research results hold significant instructive implications for the early warning and prevention strategies concerning analogous geological disasters in reservoir areas.
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Key words:
- rock mass deterioration /
- stability /
- Three Gorges Reservoir /
- buckling mode
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图 2 黄岩窝危岩体沿江分布及计算剖面选取
注：a为底座岩溶凹腔；b为后缘边界裂缝。
Figure 2. Distribution along the Yangtze River and selection of calculation profiles for Huangyanwo dangerous rock mass
图 3 单绳升降技术（SRT）调查岩壁卸荷裂隙
Figure 3. Illustration graph of investigation on rock face unloading cracks by single rope lifting technique（SRT）
图 5 黄岩窝W1号危岩体工程地质剖面图
Figure 5. Engineering geological profile of Huangyanwo W1 dangerous rock mass
图 6 黄岩窝西段数值计算模型
1—基岩； 2—岩溶掏蚀区； 3—危岩体； 4—X方向速度约束； 5—软弱区； 6—折减区域； 7—X、Y方向速度约束； 8—潜在滑移面； 9—卸荷裂缝。
Figure 6. Numerical calculation model of the western section of Huangyanwo
图 10 工况二第40个周期最大剪应变云图
Figure 10. Nephogram of maximum shear strain during the 40th cycle of working condition Ⅱ
图 11 工况二第40个周期总位移云图
Figure 11. Cloud diagram of total displacement in the 40th cycle of working condition Ⅱ
图 12 稳定性系数变化图
Figure 12. Broken line diagram of stability coefficient variation graph under compound conditions
表 1 危岩单体形态特征
Table 1. Morphological characteristics of the dangerous rock mass monomer
危岩
编号危岩形态 体积
/m3主崩方向
/（°）宽/m 高/m 厚/m W1 280～300 100～120 20～41.30 540000 3 W2 100～120 100～110 25～32 360000 2 W3 20～50 70 9 22050 352 W4 50 30～45 5 9000 4 W5 28～35 90～100 7 18480 1 W6 20 65 4 5200 2 合计 — — — 954730 — 
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表 2 黄岩窝危岩体物理力学参数表
Table 2. Physical and mechanical parameters of Huangyanwo dangerous rock mass
岩性 重度/（kN·m−3） 弹性模量/MPa 泊松比 黏聚力/MPa 内摩擦角/（°） 抗拉强度
/MPa灰岩（基岩） 26.82 50 400 0.20 5.48 44.4 2.71 灰岩（危岩体） 26.91 27 200 0.33 1.79 37.6 2.71 灰岩（破碎带） 26.82 27 200 0.33 1.79 37.6 2.71 结构面 黏聚力/MPa 内摩擦角/（°） 抗拉强度
/MPa法向刚度
/（MPa·m−1）切向刚度
/（MPa·m−1）1.534 34.34 0.542 40 000 10 000
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表 3 传统公式法计算的稳定性系数
Table 3. Stability coefficients calculated by traditional formula method
库水位/m 175 145 稳定系数 抗滑移 2.60 2.61 抗倾覆 2.49 2.51
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表 4 数值计算工况表
Table 4. Numerical computational conditions table
工况一 1-1：自重+145 m水位 1-2：自重+175 m水位 1-3：自重+145 m库水位+暴雨 工况二 2-1/10自重+145 m水位+岩体强度劣化 工况三 3-1/10自重+175 m水位+岩体强度劣化 工况四 4-1/10自重+145 m水位+暴雨+岩体强度劣化 工况五 5-1/10自重+175 m水位+暴雨+岩体强度劣化
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