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THE IMPLICATION AND EVALUATION OF TOPPLING FAILURE IN ENGINEERING GEOLOGY PRACTICE
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摘要: 近10年来，在山区，尤其是西部山区的工程建设和灾害防治实践中，我们发现越来越多的以“倾倒”为特征的岩质边坡变形破坏和稳定性问题，其出现的频度和造成的危害大有比肩“滑动”破坏这一边坡失稳的传统主题，成为困扰地质工程师和岩石力学工作者的又一难题。这类问题之所以难，是因为建立在以“滑动”为基础的传统边坡稳定性分析方法不再适用这类边坡。本文在大量工程实例的基础上，分析了边坡倾倒变形和破坏的基本特征，从“倾倒”变形破坏的地质过程和变形稳定性分析的基本理念出发，建立了描述倾倒边坡不同变形程度的工程地质模型，这个模型将倾倒边坡分为倾倒-坠覆、倾倒-错动、倾倒-张裂、倾倒-松弛4个区，分别对应不同的变形程度和稳定性状况，提出了各个区的具体特征和定性指标与量化指标相结合的描述指标体系，从而将倾倒的地质显现、力学机理和变形稳定性有机统一，实现了对倾倒边坡稳定性的工程地质评价。与传统的“滑动”问题不同的是，本文没有强调对这类问题采用强度稳定性的评价思路，而建议采用变形稳定性评价的理念，这似乎更适合倾倒变形这类问题的分析和评价。Abstract: An increase in the number of rock slope instability case that was characterized with "toppling" movement was found in the practice of engineering geology in west China in the past decade. The significance of the potential threats caused by toppling failure has arguably moved abreast of that induced by the conventional slope movement type commonly known as "sliding", and thus it has become a more pronounced challenge faced by engineering geologists and geotechnical engineers. The critical issue in the study of toppling failure is that the current analytical and/or empirical models are primarily based on the hypothetical slide of rock slopes without considering other forms of movement. The paper analyzes the deformation and failure process of toppling movement in light of the field data obtained from a large number of engineering projects. The study of toppling movement presented here constructed engineering geology models to depict the deformation at various stages and divided the movement into the types of toppling-falling, toppling-slipping, toppling-cracking, and toppling-loosening, which provides systematic qualitative descriptions and quantitative thresholds for the characteristics of each movement type. The study aims at unifying the understanding of geological significance, static and dynamic mechanics, and slope stability analysis to provide means of evaluating the stability of rock slopes prone to toppling failure. The slope stability evaluating criteria are primarily based on deformation process compare to the previous criteria utilizing strength to assess the stability of slope subject to sliding movement.
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Key words:
- Overlap /
- Stability /
- Reverse slope /
- Geological model
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图 1 青藏高原东侧倾倒变形破坏分布及其与变质岩地层(各类板岩、片岩)分布的关系
Figure 1. Distribution of metamorphic rocks(slates and schist) and locations of toppling failure of slopes in southwestern China
图 3 边坡倾倒与边坡坡度(β)、岩层倾角(α)的关系
Figure 3. Relationship between toppling occurrence and slope angle, dip angle of rock strata
图 4 倾倒深度与岩层倾角(α)的关系
Figure 4. Relationship between strata dip angles and toppling depth
图 5 模型试验斜坡倾倒深度与岩层倾角、坡角的关系(据黄润秋等，1994)
Figure 5. Relationship between toppling depth and dip angle of rock strata and slope angle obtained by base friction tests
图 7 边坡浅层脆性倾倒
a.边坡浅层倾倒变形；b.浅层倾倒的结构变形
Figure 7. Basic model of shallow toppling failure of a slope
图 9 雅砻江锦屏水电站水文站坝址由深层倾倒形成的滑坡(左为岬吧滑坡，右为水文站滑坡剖面)
Figure 9. Landslide formed by deep-seated toppling at Jinping hydropower in Yalong river
图 10 斜坡倾倒-错动复合变形模式
Figure 10. A composite deformation of toppling deformation and slipping in a slope
图 11 小湾水电站饮水沟及2#山梁1 460~1 600m坡面开挖地质素描图
Figure 11. Sketch map of slope toppling deformation at Xiaowan dam-site, Lancang river
图 12 小湾水电站饮水沟1500~1520m马道A-A坡面开挖地质素描示意图g1~g10：片岩夹层；f1~f4：小断层、挤压带
Figure 12. Sketch of toppling deformation of rock strata at 1500~1520m elevation at Xiaowan dam-site
图 13 高程1500m岩层倾角沿马道变化曲线
Figure 13. Variation of dip angle of rock strata at elevation of 1500m
图 15 岩体倾倒变形破裂发展过程
a.弱倾倒-层间剪切滑移；b.强倾倒-层间拉张破裂；c.强倾倒-切层张剪破裂
Figure 15. Process of toppling deformation and fracturing
图 16 澜沧江苗尾水电站边坡倾倒的工程地质剖面
Figure 16. Cross section of slope deformation and zonation at Miaowei dam-site, Langcang river
表 1 西南地区典型倾倒边坡变形破坏实例
Table 1. Some examples of toppling deformation and failure
序号 边坡或灾害点 边坡状态 坡高/m 坡度/(°) 岩性及其组合 岩层倾角/(°) 倾倒折断深度/m 备注 1 雅砻江锦屏水电站解放沟-三滩坝址 倾倒变形 >500 40~50 T3变质砂岩、板岩，炭质板岩 50~60 330 深层 2 雅砻江锦屏水电站水文站滑坡 滑坡 300 20~30 T3变质砂岩、板岩，炭质板岩 40~50 250 深层 3 雅砻江锦屏水电站呷巴滑坡 滑坡 450 20~30 T3变质砂岩、板岩，炭质板岩 60~70 约300 深层 4 雅砻江锦屏水电站木里桥边坡 倾倒变形 变质砂岩、板岩 深层 5 金沙江溪洛渡水电站库区星光3组变形体 上硬下软，倾倒变形强烈 32~39 泥灰岩、泥质细砂岩及砂质页岩 75~85 浅层 6 澜沧江小湾水电站饮水沟堆积体 倾倒变形(上部) 200 30~40 花岗片麻岩，绢云母片岩、板岩 70~80 150~200 深层 7 澜沧江小湾水电站6号山梁 倾倒变形 >200 35~40 花岗片麻岩 70~80 30~40 浅层 8 澜沧江苗尾水电站坝址区 倾倒变形 >300 35~45 板岩、片岩夹变质砂岩 50~60 150~200 深层 9 澜沧江黄登水电站右岸1#沟 倾倒变形 350 35~45 75 深层 10 澜沧江黄登水电站右岸7#沟 倾倒变形 350 35~45 70~80 深层 11 澜沧江古水水电站 倾倒变形 >300 20~45 板岩，砂岩，变质玄武岩 75~85 12 澜沧江如美水电站坝址区 倾倒变形 >300 30~40 英安岩，受平行岸坡节理切割 70~80 50~70 中等 13 黄河拉西瓦水电站 倾倒变形 500 40~50 花岗岩，受平行岸坡节理切割 70~85 30~60 浅层 14 四川杂谷脑河二古溪边坡 倾倒变形 >400 30~40 板岩、绢云母片岩夹变质砂岩 50~60 >100 深层 15 四川杂谷脑河西山村滑坡群(10余个) 滑坡 >500 20~35 板岩、绢云母片岩夹变质砂岩 65~75 >150 深层 16 四川安县白什乡滑坡 变形体，滑坡 >400 40~50 板岩、绢云母片岩夹变质砂岩 50~60 >80 深层 17 西藏加查 变形体，滑坡 150 >45 变质岩 30~40 20~50 浅层 
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表 2 坝区倾倒岩体的单位拉张量λ/mm ·m-1
Table 2. Unite tension amount of rock layers for different toppling types
倾倒变形分级 硬质岩 软质岩 备注 极强倾倒破裂A 26.8~47.4 未区分 强倾倒变形B 上段B1 20.5~33.1 10.3~32.9？ 下段B2 14.9~26.5 11.1~29.4？ 弱倾倒变形C 10.0~16.6 8.3~11.9？
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表 3 实测倾倒岩体纵波波速VP值
Table 3. VP values for different types of toppling
倾倒变形分级 VP平均值范围/m·s-1 备注 极强倾倒破裂A 1017~1405 强倾倒变形B 上段B1 1290~2111 下段B2 1845~3000 弱倾倒变形C 1852~3377
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表 4 斜坡深层倾倒变形分级体系
Table 4. Classification system of deep seated toppling deformation for slopes
特征描述及指标 极强倾倒折断破裂A 强倾倒破裂B 弱倾倒过渡变形C 上段B1，切层剪张破裂 下段B2，层内张裂变形 变形破裂特征 岩体强烈倾倒折断、坠覆，整体裂松弛，局部架空 岩体强烈倾倒，层内强烈拉张，整体较松弛，张剪性缓裂面切层发展 倾倒较为强烈，层内拉张破裂较强烈，张裂面一般不切层，局部切单层 岩体倾倒变形较弱，层内错动带剪切位错，层内岩体微量张裂变形 岩层倾角(倾倒角)α/(°) 硬质岩 ≤40(>35~40) 34~54(20 < α≤35) 50~69(10 < α≤20) 64~78(α≤10) 软质岩 ≤35(>40) 32~50(25 < α≤40) 51~66(15 < α≤25) 58~74(α≤15) 最大拉张量s/mm 范围值 4.0~55.0 5.0~70.0 2.0~65.0 0~17.0 平均值 28.0 26.0 15.0 5.0 单位拉张量λ/mm·m-1 硬质岩 27.0~50.0 20.0~33.0 15.0~27.0 10.0~17.0 软质岩 10.0~33.0 10.0~30.0 8.5~12.0 卸荷变形 强卸荷 强卸荷 总体强卸荷，下部可为弱卸荷 弱卸荷 风化特征 强风化 一般为弱风化上段，上部为强风化 总体弱风化上段，下部为弱风化下段 总体弱风化下段，部分微新岩体 岩体结构类型 碎裂架空结构，散体结构 层状块裂-碎裂结构 层状-块裂结构 层状-似层状结构 纵波波速VP/m·s-1 1000~1500 1500~2000 2000~3000 3000~4000 岩体类别 Ⅴ~Ⅵ类 Ⅲ1类 Ⅲ2类 Ⅱ类 稳定性系数类比值 1.0~1.05 1.05~1.15 1.15~1.25(有深层折断面时另行评价) >1.25
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表 5 斜坡浅层倾倒变形分级体系
Table 5. Classification system of slope shallow toppling deformation
特征描述及指标 倾倒-折断A 倾倒-张裂B 倾倒松弛C 卸荷松弛D 岩体变形破裂特征 强烈的倾倒-折断，岩体拉张破裂、松弛解体，局部出现宏观坠覆位移 弱倾倒、强张裂，伴有岩板内部拉张裂 轻微倾倒变形，岩板间张裂，处于张裂-松弛状态，整体性较好 无倾倒，弱松弛，岩体整体性较好 岩体结构 碎裂-块裂架空结构，局部散体状 层状块裂-碎裂结构 层状-似层状-块裂结构 层状-似层状结构 岩板倾倒角α/(°) 18~35 5~15 < 未倾倒 卸荷 极强卸荷 强卸荷，局部弱卸荷 弱卸荷 局部松弛 风化 强风化 强风化，局部弱风化 弱风化-微风化 微风化-新鲜 最大拉张量/mm 280.0 40.0~95.0 20.0~30.0 10.0~20.0 纵波波速VP/m·s-1 800~1300 1100~2500 2200~3000 3200~4200 岩体类别 Ⅴ~Ⅵ类 Ⅲ1类 Ⅲ2类 Ⅱ类 稳定性系数类比值 1.0~1.05 1.05~1.20 1.20~1.30 ＞1.30
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