Genetic Types of Large-Scale Landslides Induced by Wenchuan Earthquake
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摘要: "5·12"汶川地震诱发了数以万计的滑坡灾害, 其中仅大型滑坡就上百处.通过对汶川地震诱发的20余处大型滑坡的变形破坏特征进行深入调研, 结合振动台试验和数值模拟等手段, 发现汶川地震诱发大型滑坡的变形破坏模式和内在力学机制与常规重力作用下滑坡机制具有显著的不同.在强震条件下, 斜坡中上部地震水平加速度可超过1g, 其地震水平惯性力远远超过岩体的抗拉强度, 地震作用首先在坡体后缘形成与坡面平行且陡倾坡外的深大拉裂缝, 随后拉裂岩体的底部产生剪切滑移, 最终形成滑坡.在强震条件下, 斜坡岩体最基本的变形破坏单元就是拉裂和剪切滑移, 且以拉裂占主导.不同的斜坡结构, 其底部剪切滑移会沿不同的结构面发生.根据滑源区所处的地质环境条件、坡体结构以及岩性组合特征, 将汶川地震诱发的大型滑坡划分为五类成因模式: 拉裂—顺走向滑移型、拉裂—顺层(倾向)滑移型、拉裂—水平滑移型、拉裂—散体滑移型、拉裂—剪断滑移型.Abstract: The "5·12" Wenchuan earthquake induced thousands of landslides, including hundreds of large-scale ones. The deformation and destroy characteristics of 20 large-scale landslides induced by Wenchuan earthquake found in our in-depth investigation and extensive survey, combined with the tools of shaking table test and numerical simulation, we find that their deformation and destroy model and intrinsic mechanical mechanism Wenchuan earthquake are significantly different from those of landsides induced by routine gravity. On the condition of strong shock, the earthquake-horizontal acceleration on the middle-top of the declivity can exceed 1g, and its earthquake horizontal inertia enormously exceeds the tension strength of the rock mass. Seismic action firstly shaped a deep large fissure which was parallel to the clinohedron on the back of the slope, and then the bottom of the pull-apart rock mass engendered shearing glide, finally, there induced landslide. On the condition of strong shock, the most essential deformation and destroy element of the slope rock mass are tension-cracks and shearing glide, and mainly dominated by tension-cracks. With different slope structures, the bottom shearing glide occurs with different discontinuities. According to the geological environment of the landsliding source region as well as the characteristics of the slope form and lithological association, this paper divides the large-scale landslides induced by Wenchuan earthquake into five genetic types, namely, tension-cracking and consequent sliding, tension-cracking and bedding sliding, tension-cracking and horizontal sliding, tension-cracking and scattering sliding and tension-cracking and shearing sliding.
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Key words:
- Wenchuan earthquake /
- large-scale landslide /
- genetic types /
- shearing sliding /
- engineering geology
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图 1 青川县东河口滑坡后缘陡直粗糙的拉裂壁
Fig. 1. Steep scarp with coarse cracks from Donghekou landslide, Qingchuan
图 2 自重作用下(a)和强震作用下(b)斜坡岩体的典型变形破坏模式
Fig. 2. Typical deformation and failure mode of the slope rock under self-weight operative force (a) and strong shock (b)
图 5 大光包滑坡鸟瞰(镜头指向NE向即主滑方向)
Fig. 5. Aerial view of Daguangbao landslide with main sliding direction of NE
图 7 平武县郑家山1#滑坡剖面及成因模式
Fig. 7. Typical longitudinal section and genetic mode of No.1 landslide, Zhengjiashan
图 8 青川县东河口滑坡剖面
1.碎块石；2.硅质板岩；3.炭质板岩；4.千枚岩；5.震后地形线；6.岩层产状；7.震旦系元吉组上段；8.寒武系邱家河组；9.震前地形线；10.震旦系元吉组中段；11.寒武系油房组；12.沉凝灰质砂岩；13.沉凝灰岩；14.白云质灰岩；15.块碎石土；16.地层界线；17.河流；18.石坎断层(逆冲走滑)
Fig. 8. Geological section of Donghekou landslide, Qingchuan
图 9 东河口滑坡发生后在滑源区留下一巨大凹槽
Fig. 9. Large trough left in the source area after Donghekou landslide
图 11 北川中学新区滑坡堆积区主要为散体的大块石
Fig. 11. Large blocks in the deposition of Beichuan new middle school landslide
图 12 拉裂-剪断滑移型滑坡变形破坏过程
Fig. 12. Failure process of typical landslide with tension-cracking and shearing
图 13 平武县郑家山2#滑坡变形破坏模式
Fig. 13. Longitudinal section and deformation and failure mode of No.2 landslide, Zhengjiashan
表 1 汶川地震诱发大型滑坡典型成因模式
Table 1. Typical genetic types of lager-scale landslides induced by the Wenchuan earthquake
成因模式 形成条件 基本特征 典型滑坡实例 拉裂-顺走向滑移型 斜坡岩体由缓-中缓倾坡内的层状岩体组成，坡体内发育两组分别与岩层走向和倾向近于平行的陡倾长大结构面，在斜坡走向方向某一侧具有较好的临空条件. 强震作用下，斜坡岩体以山体内侧顺坡向陡倾结构面作为内侧边界，追踪顺倾向方向的陡倾结构面产生后缘拉裂面，基于底部层间(内)软弱面，沿岩层走向向临空条件较好的一侧发生滑动. 安县大光包滑坡、青川窝前滑坡 拉裂-顺层(倾向)滑移型 中-陡倾角的顺层斜坡 在地震强大的惯性力作用下，坡体中、上段岩体沿顺层软弱面(岩层层面、软硬岩接触界面、层内弱面等)产生拉裂变形，使该面大部分内聚力丧失，随后在地震动力的持续作用下沿该拉裂面发生高速顺层滑动. 北川唐家山滑坡、平武郑家山1#滑坡 拉裂-水平滑移型 近水平缓倾坡外的基岩斜坡 在强大的水平地震惯性力作用下，斜坡后缘首先产生陡倾坡外的竖向深大拉裂面，裂面外侧的岩体在后续地震动力作用下沿顺层弱面发生整体滑出.滑坡一般出露于斜坡中上部，滑源区下部一般为一陡坎，滑体以一定的初速度水平滑出后，往往会越过陡坎作一段距离的临空飞跃，呈现出水平抛射的特点. 青川东河口滑坡、青川大岩壳滑坡 拉裂-散体滑移型 由灰岩、花岗岩等硬岩构成的斜坡，数组结构面将斜坡岩体切割成大多相互分离的岩块 强烈的地震动力作用，首先使斜坡浅表层的块状岩体震裂松动，进而在持续的地震动力作用下逐渐解体，直至最后呈散体状整体滑动失稳. 北川中学新区滑坡、青川石板沟滑坡 拉裂-剪断滑移型 反倾坡内的层状结构斜坡或块状结构斜坡 在地震强大的水平惯性力作用下，首先在坡体后缘沿一组陡倾坡外的结构面形成深大拉裂面，进一步持续的地震动力使深大拉裂缝底端产生拉裂和剪切滑移变形，形成切层滑移面，并最终沿此面滑动失稳.该类模式即可产生同震滑坡，也可形成具有一定滞后性的震后滑坡. 北川王家岩滑坡、北川陈家坝鼓儿山滑坡、青川董家滑坡、平武郑家山2#滑坡、安县罐滩滑坡 
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