Research on Effects of Spatial Structure and Strength Characteristics of Tectonic Mélanges in Baige Landslide on Formation of Sliding Zone and Long Runout Movement
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摘要:
2018年10月和11月在金沙江构造混杂岩带中段相继发生两次大型高位远程滑坡，并引发滑坡-堰塞湖灾害链，滑坡源区位于西藏自治区昌都市江达县白格村.针对白格滑坡的远程运动特性，通过室内微观特性测试分析滑坡处构造混杂岩的岩性特征，运用环境噪声频散测量探明物源区构造混杂岩的空间结构，结合不排水环剪试验剖析滑动带物质的剪切行为.研究发现，（1）滑坡物源区的构造混杂岩主要由绿泥石化变质粉砂岩和伊利石化变质板岩组成，均含有较高比例粘土矿物成分，遇水易发生风化作用导致强度降低；（2）坡体内构造混杂岩块体的分布结构显著影响滑动带的形成和形状，滑动带沿着块体和基质之间的薄弱区域扩展，在岩体内呈现“绕块体发育”模式；（3）饱和滑动带试样在长距离不排水剪切过程中产生高孔隙水压力，导致强度显著弱化，其峰值抗剪强度和残余强度降低为干燥状态下的67%和60%.结果表明，构造混杂岩的强度劣化特性和块体分布结构对滑动带的形成有显著影响，其剪切强度特性对滑坡的远程运移具有控制作用.此研究可为白格滑坡坡体后续可能的变形破坏分析提供依据，还可进一步为构造混杂岩地区边坡稳定性评价和同类型滑坡灾害防治提供参考.
Abstract:In October and November 2018, two large-scale high-altitude long-runout landslides successively occurred in the central section of the Jinsha River tectonic mélange belt, triggering a cascade disaster chain of landslide-dammed lakes. The source areas of these landslides were located at Baige Village, Jiangda County, Changdu City, Tibet Autonomous Region. This study focuses on the long runout movement characteristics of the Baige landslide. It investigated the topographic features of the landslide area through unmanned aerial vehicle (UAV) surveying. Laboratory microscopic characterization was used to analyze the lithological properties of the mélange rock. The ambient noise dispersion measurements were used to explore the spatial structure of the mélange rock mass in the source area, combined with the high-speed undrained ring shear test to analyze the dynamics of the sliding zone material.This study reveals follows. (1) The mélange rocks of the source area are primarily composed of chloritized metamorphic siltstone and illitized metamorphic slate. These rocks contain a high proportion of clay minerals, which are prone to weathering when exposed to water, leading to a reduction in strength. (2) The spatial distribution of blocks within the mélange rock mass significantly affects the formation and shape of sliding zones. Sliding zones tend to form along zones of weakness in both the blocks and the matrix, exhibiting a failure mode characterized by block-bypassing mechanisms.(3) The saturated sliding zone sample generates high pore-water pressure during undrained rapid shear process, resulting in significant strength degradation. Its peak shear strength and residual strength are 67% and 60% of that under dry conditions, respectively.The results demonstrate that the combination of the spatial structure and strength deterioration characteristics of mélanges is a key factor causing the frequency of high-altitude long runout landslides in this region. The shear strength characteristics of mélanges controlled the long-runout movement of the landslide.This research provides a foundation for the subsequent potential deformation and failure of the Baige landslide slope. It also offers valuable insights for slope stability analysis and landslide disaster prevention in tectonic mélange areas.
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图 1 白格滑坡区域地质图
修改自王国生等，1992，白玉县幅H-47-9雄松区幅H-47-15 1/20万区域地质调查报告；底图为吉林一号卫星地图
Fig. 1. Geological map of the Baige landslide area
图 2 白格滑坡地形图
由2023年4月10日滑坡现场无人机航测数据生成. a.滑坡三维点云地形图；b.滑坡地形等高线图；c.滑坡纵剖面L-L’（滑前地形源自谷歌地球）
Fig. 2. Topographic map of the Baige landslide
图 3 白格滑坡现场调查情况
a.白格滑坡物源区环境噪声频散测量BG05与BG06测线位置（修改自吉林一号卫星影像）；b.白格滑坡全貌；c.滑坡后壁渐进式破坏（b~c均由无人机拍摄）；d.滑坡后缘平台发生变形破坏后形成的张拉裂缝及倾倒的监测设备；e.滑坡后缘测试现场露头
Fig. 3. On-site investigation of the Baige landslide
图 4 滑坡物源区露头岩石样品偏光显微镜照片
a.绿泥石化变质粉砂岩BG-A；b. 高岭石化变质粉砂岩（方解石化）BG-B；c. 伊利石化变质板岩（含细砂粉砂）BG-C；d. 绿泥石化变质粉砂岩BG-D.Pl. 斜长石；Chl. 绿泥石；Ser. 绢云母；Lm. 褐铁矿
Fig. 4. Photographs of rock samples from the source area of the landslide under optical microscope
图 5 白格滑坡物源区岩样X射线衍射粘土矿物测试图谱
a.未经处理的自然样品；b.饱和乙二醇处理样品；c.450 ℃高温处理后样品
Fig. 5. X-ray diffraction patterns of clay mineral components in rock samples from the source area of the Baige landslide
图 6 白格滑坡物源区环境噪声频散测量结果
a. 测线BG05；b. 测线BG06
Fig. 6. Results of ambient noise dispersion measurements in the source area of the Baige landslide
图 7 ICL-2不排水环剪试验情况
a. 滑动带试验样品（砾石土）；b. 筛分后试样；c. 干燥条件下环剪后；d. 饱和条件下环剪后
Fig. 7. Conditions of ICL-2 undrained ring shear test
图 8 干燥试样在排水条件下进行速度控制时环剪测试的结果（剪切速率为2 mm/s）
a. 剪切阻力随剪切位移的变化（正应力控制在600 kPa）；b. 应力路径与破坏线
Fig. 8. Results of speed-controlled ring shear test on dry samples (shear rate = 2 mm/s)
图 9 饱和不排水条件下滑动带物质速度控制下环形剪切试验结果（剪切速率为2 mm/s, BD=0.95）
a. 剪切阻力与孔隙水压力随剪切位移的变化；b. 应力路径与破坏线
Fig. 9. Results of speed-controlled ring shear test on sliding zone materials under saturated undrained conditions (shear rate=2 mm/s, BD=0.95)
表 1 白格滑坡物源区岩样X射线衍射粘土矿物定量分析结果
Table 1. X-ray diffraction quantitative analysis results of claymineral components in rock samples from the source area of the Baige landslide
样品编号 粘土质组分形成的变质矿物占比 粘土矿物主要矿物及相对质量百分比（%） 伊利石（It） 高岭石（Kao） 绿泥石（C） BG-A 25% 5 / 95 BG-B 20%~30% 41 50 9 BG-C 25%~30% 95 / 5 BG-D 20%~25% 5 / 95 
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