Analysis of the formation mechanism of landslide in Changchong Group, Songtao, Guizhou
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摘要: 贵州省属于典型的岩溶山区，第四系覆盖层分布空间分布不均匀，具体表现在坡体前缘到中部浅表层为粘性土，后缘为碎石土，随着基覆界面的起伏在垂直方向上厚度差异大，近年来因气候变化异常，极端降雨、暴雨的天数增多，导致强降雨过后浅表层突发性的土质滑坡具有较强的群发现象，基于此这篇论文以贵州省松桃县大路镇和平社区长冲组滑坡为研究对象，通过实地跟踪调查、工程地质钻探、岩土试验以及FLAC3D软件模拟等手段，探究降雨前后该滑坡外形特征、岩土结构特征和变形破坏历程，以此来解析该类滑坡的变形破坏过程及发生机理。结果表明：1）该滑坡为推移式滑坡，其特殊的地形地貌与地层岩性为滑坡发生提供内在因素；2）降雨是本滑坡的主要诱发因素，滑坡发生过程可总结为后缘饱和推压阶段-暂态饱和区扩散变形演进阶段-前缘破坏临空阶段-整体破坏阶段；3）该滑坡发生的机理主要是在降水因素诱发渗透力变化与坡体重度变化共同作用下导致滑坡体失稳变形。该项探索能为我们更清楚的认识降雨型滑坡早期识别因子以及能够更好更快进行管控和治理提供一定的理论基础。Abstract: Guizhou Province is a mountainous region with typical karst topography where the quaternary overburden layer is unevenly distributed, with clayey soil on the shallow surface layer from the front edge to the middle of the slope body and gravelly soil at the rear edge. This geological characteristic, combined with the increase of extreme rainfall and heavy rainfall due to abnormal climate change in recent years, has resulted in a rise of sudden earth landslides in the shallow surface layer after strong rainfall. To investigate this phenomenon, the Changchong Group landslide in Heping Community, Dalu Town, Songtao County, Guizhou Province was studied through field tracking survey, geological drilling, geotechnical testing, and FLAC3D software simulation. The study uses various methods to investigate the shape and geotechnical structure characteristics, and deformation and damage history of the landslide before and after rainfall, in order to analyze the failure process of such landslides and their occurrence mechanism. Results show that: (1) The landslide is a thrust load-caused landslide, and its unique terrain and lithology characteristics provide intrinsic factors for the occurrence of the landslide. (2) Rainfall is the main triggering factor of landslide, and the occurrence process of the landslide can be summarized as follows: a) rear saturated pushing stage, b) transient saturated diffusion and deformation evolution stage, c） front edge overhanging failure stage, and d) overall failure stage. (3) The mechanism of the landslide is mainly due to the combined effect of the changes in permeability induced by precipitation and the slope gravity change, which led to the instability and deformation of the landslide. The study provides insight into the early identification factors of rainfall landslides and provides a theoretical basis for better and faster control and management.
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图 3 1-1′工程地质剖面图
Figure 3. Longitudinal geological profile for cross-section 1-1′（refer to Fig.2）
图 4 裂缝发育现状
（a）中后部滑动特征;（ b）坡体滑动造成房屋倾斜
Figure 4. Site photo of the developing fracture of landslide
图 5 降雨入渗过程中孔压、变形和位移演化图
Figure 5. Distribution of pore pressure, displacement and stress analysis during landslide development stages under precipitation condition (FLAC3D software simulation)
图 6 降雨入渗过程中孔压、变形和位移随时间的变形曲线图
Figure 6. Distribution of pore pressure, displacement and stress analysis at different landslide development stages against duration
表 1 变形裂缝统计表
Table 1. Summary characteristics of deformation cracks of the studied landslide
裂隙编号 裂隙方向 初现时间 发育特征 性质 L1 33～36° 2014年7月16日 位于滑坡后缘，第四系粘土与基岩接触面附近，滑坡滑动形成的拉张裂缝，裂缝呈直线型，与主滑方向垂直，裂缝张开度约4～20 cm，可见深度约0.3～0.5 m，下错高度约0.3～0.5 m，延伸长度约为18 m。 张拉裂缝 L2 32～35° 2015年8月18日 位于滑坡后缘耕地中，滑坡滑动形成的拉张裂缝，裂缝呈直线型，与主滑方向垂直，裂缝张开度约2～10 cm，可见深度约0.2～0.5 m，下错高度约0.1～0.3 m，延伸长度约为16 m。 张拉裂缝 L3 37～42°，320～325° 2014年7月16日 从滑坡后缘呈弧形一直延伸至滑坡前缘，裂缝走向37～42°转向320～325°，为滑坡滑动形成的拉张裂缝和剪切裂缝，裂缝张开度约30～60 cm，可见深度约1～1.5 m，下错高度约0.3～0.6 m，延伸长度约为50 m，该裂缝是滑坡规模最大的一条裂缝。 张拉、
剪切裂缝L4 32～35° 2014年8月17日 位于滑坡中部，滑坡滑动形成的拉张裂缝，裂缝呈直线型，与主滑方向垂直，裂缝张开度约4～14 cm，可见深度约0.4～0.8 m，下错高度约0.1～0.4 m，延伸长度约为15 m。 张拉裂缝 L5 45～55° 2014年10月31日 位于滑坡中部，滑坡滑动形成的拉张裂缝，裂缝呈弧形，与主滑方向近垂直，裂缝张开度约4～15 cm，可见深度约0.5～1 m，下错高度约0.2～0.5 m，延伸长度约为14 m。 剪切裂缝 L6 45～55° 2015年8月18日 位于滑坡中部，滑坡滑动形成的拉张裂缝，裂缝呈弧形，与主滑方向近垂直，裂缝张开度约4～20 cm，可见深度约1～2 m，下错高度约0.3～0.5 m，延伸长度约为25 m。 剪切裂缝 L7 320～355° 2014年7月16日 位于滑坡中部水池东南面，滑坡滑动形成的拉张裂缝，裂缝呈直线形，裂缝张开度约10～20 cm，可见深度约0.2～0.3 cm，延伸长度约15 m。 张拉裂缝 L8 35～38° 2015年9月19日 位于滑坡中部竹林中，滑坡滑动形成的拉张裂缝、剪切裂缝，裂缝呈弧形，与主滑方向近垂直，裂缝张开度约20～40 cm，可见深度约0.5～1 m，下错高度约为0.2～0.4 m，延伸长度22 m。 张拉裂缝 L9 350～361° 2014年7月16日 位于滑坡中部竹林中，滑坡滑动形成的剪切裂缝，裂缝呈弧形，裂缝张开度约20～50 cm，可见深度约0.2 m，下错高度约为0.4～0.8 m，延伸长度约20 m。 剪切裂缝 L10 322～327° 2014年7月18日 位于滑坡中前部房屋旁，滑坡滑动形成的剪切裂缝，裂缝呈直线形，裂缝张开度约5～8 cm，可见深度约0.1～0.2 m，延伸长度约10 m。 张拉裂缝 L11 320～325° 2014年7月16日 位于滑坡中前部房屋旁，滑坡滑动形成的剪切裂缝，裂缝呈直线形，裂缝张开度约5～10 cm，可见深度约0.1～0.3 m，延伸长度约15 m。 张拉裂缝 
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