Failure process and long-term stability analysis of typical unstable rock mass in the Three Gorges Reservoir area considering rock mass deterioration
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摘要:
自三峡库区蓄水以来, 岸坡消落带岩体劣化趋势明显, 加速了岩质岸坡向欠稳定和不稳定发展, 潜在崩塌涌浪灾害威胁长江航道安全。以三峡库区板壁岩为例, 采用抗剪强度折减法分析在岩体劣化工况下危岩体的破坏过程与长期稳定性。结果表明: 在自然工况下, 板壁岩危岩体处于稳定状态; 在库水+岩体劣化工况下, 中部锁固段处拉应力集中, 拉张裂缝逐步向顶部主控裂缝及底部基破碎带延展并相互贯通, 可能发生滑移-剪切破坏; 在库水+岩体劣化+强降雨极端工况下, 约40个水文周期后, 岩体强度下降30%, 板壁岩危岩体的稳定性系数降至约1.14, 处于欠稳定状态, 建议进行工程防治, 提高危岩体稳定性, 以保障航道安全。研究结果可为三峡库区板壁岩及类似危岩体的防灾减灾工作提供科学合理的依据。
Abstract:Since the Three Gorges Reservoir went into service, the rock mass in the hydro-fluctuation belt of the bank slope has obviously deteriorated, which accelerates the instability of the bank slope. The potential debris avalanche threatens the safety of the Yangtze River waterway. The Banbiyan unstable rock mass in the Three Gorges Reservoir area was studied using the shear strength reduction method to analyze the failure process and long-term stability of the unstable rock mass under rock deterioration. The results show that the Banbiyan unstable rock mass is stable under natural working conditions. Under reservoir water and rock mass deterioration, the tensile stress is concentrated at the central section. The tensile cracks gradually penetrate up and down, extending to the prominent controlling cracks at the top and the bottom base fracture zone. Slip-shear failure may occur. Under the condition of reservoir water combined with rock mass deterioration and heavy rainfall, the strength of the rock mass decreases by 30% after about 40 hydrological cycles, and the stability coefficient of the Banbiyan unstable rock mass decreased to about 1.14, which is an under-stable state. It is suggested to carry out engineering prevention and control to improve the stability of dangerous rock mass to ensure the safety of the waterway. The research results can provide a scientific and reasonable basis for disaster prevention and mitigation of the Banbiyan and similar unstable rock masses in the Three Gorges Reservoir area.
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图 2 板壁岩危岩体破碎带及裂隙分布图
Figure 2. Map showing the fracture zones and fissures in the Banbiyan unstable rock mass
图 3 板壁岩危岩体工程地质剖面图
Figure 3. Engineering geological profile of the Banbiyan unstable rock mass
图 5 W1危岩体边界
a—右边界；b—左边界
Figure 5. Boundary of the W1 unstable rock mass
(a) Right boundary; (b) Left boundary
图 6 基座破碎带特征照片
a—上游危岩体；b—下游危岩体
Figure 6. Field photos showing the features of the foundational fracture zones
(a) Unstable rock mass on the upstream side; (b)Unstable rock mass on the downstream side
图 7 板壁岩危岩体连续-非连续数值模型
Figure 7. Continuous-discontinuous numerical model for the Banbiyan unstable rock mass
图 8 位移及屈服单元云图
a—工况1；b—工况2-1
Figure 8. Cloud diagram showing the displacement and yield element
(a) Under working condition 1; (b) Under working condition 2-1
图 9 塑性区分布过程图(工况2-1)
Figure 9. Diagram showing the extension of the plastic zone (Under working condition 2-1)
图 10 工况2稳定性系数与最大位移量随时间的关系
a—工况2-1；b—工况2-2
Figure 10. Stability coefficient versus maximum displacement as a function of time under working condition 2
(a) Under working condition 2-1; (b) Under working condition 2-2
图 11 位移及屈服单元云图
a—工况3-1；b—工况3-15
Figure 11. Cloud diagram showing the displacement and yield element
(a) Under working condition 3-1;(b) Under working condition 3-15
图 12 工况3稳定性系数与最大位移量随时间的关系
Figure 12. Stability coefficient versus maximum displacement as a function of time under working condition 3
图 13 板壁岩危岩体稳定系数-时间过程曲线
Figure 13. Stability coefficient-time course curves of the Banbiyan unstable rock mass
表 1 板壁岩单体危岩体特征表
Table 1. Characteristics of the Banbiyan unstable rock mass
危岩体编号 是否涉水 整体发育形态 最低基底高程/m 危岩体顶部与基底相对高差/m 破坏方向/(°) 方量/m3 W1 涉水 呈不规则板柱状 ~97 ~162 348 71.78×104 W2 未涉水 呈不规则棱柱体 ~194 ~60 348 1.69×104 W3 未涉水 呈薄板状 ~234 ~23 330 685 
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表 2 板壁岩危岩体灰岩物理力学指标标准值
Table 2. Standard values of physical and mechanical indexes of the limestone from the Banbiyan unstable rock mass
状态 重度/(kN/m3) 弹性模量/×104 MPa 泊松比 抗压强度/MPa 抗拉强度/MPa 黏聚力/MPa 内摩擦角/(°) 灰岩 天然 0.0268 0.69 0.22 21.71 0.46 1.35 37.49 岩体 饱和 0.0269 18.21 0.40 1.08 35.69
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表 3 板壁岩危岩体稳定性系数计算工况
Table 3. Working conditions for calculating the stability coefficient of the Banbiyan unstable rock mass
工况1 工况2 工况3 自然工况 库水+岩体劣化工况 库水+强降雨+岩体劣化工况 1-1：自重+145 m水位
1-2：自重+175 m水位
1-3：自重+175 m水位+强降雨2-1：自重+145 m水位+岩体劣化
2-2：自重+175 m水位+岩体劣化
15个子工况，每个子工况岩体强度下降3%自重+强降雨+175m水位+岩体劣化
15个子工况，每个子工况岩体强度下降3%
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