Shear Strength Characteristics of Sliding Zone Soils and Mechanisms of Luanshibao Long Runout Landslide in Litang County, Sichuan Province, China
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摘要: 高位远程滑坡具有高位剪出、高速滑动与强动力剪切等特征，由于高速滑动过程中路径松散层饱水特性不同，其滑坡的高速远程滑动机制也存在差异.四川理塘乱石包高位远程滑坡运动路径松散层饱水，在滑坡发育特征调查的基础上，基于ICL-2高速环剪仪，对滑带土开展了200 kPa、400 kPa和600 kPa等不同法向应力下的高速不排水环剪试验，剪切速度为50 cm/s，剪切距离为300 m.试验结果表明，滑带的演化可以划分为初始剪缩、剪胀-剪缩、假剪胀、压缩排水等4个阶段，孔隙水压力呈非线性增长，与法向位移具有正相关性，在剪切距离至100 m时，孔隙水压力可上升至总应力的50%以上，颗粒破碎及其导致的滑带液化是滑带土抗剪强度降低的主要原因，滑带液化会导致试样剪切强度降低50%以上，孔隙水压力上升至总应力70%以上.乱石包滑坡的形成过程可概括为：地震作用-高速启滑、滑体解体碎屑化、滑带液化促进碎屑流远程运动、滑体减速堆积.研究成果可为运动路径松散层饱水型高位远程滑坡长距离滑动机制研究提供参考.Abstract: High-altitude and long-runout landslides exhibit typical characteristics including slip initiation at high altitudes, rapid sliding speeds, and intense dynamic shearing. These landslides exhibit differences in their long runout mechanisms due to variations in saturation characteristics of loose layers along their sliding path during high-speed sliding. This study examines the Luanshibao landslide in Litang County, Sichuan Province, which has a runout zone composed of saturated deposit. After a comprehensive investigation and analysis of the landslide characteristics, it conducted high-speed undrained ring shear tests at various normal stress levels of 200 kPa, 400 kPa, and 600 kPa using an ICL-2 high-speed ring shear apparatus. The test shearing speed was maintained at 50 cm/s, with a shearing distance of 300 m. The experimental findings indicate that the formation of the sliding zone can be divided into four stages: initial dilation, dilation-negative dilation, unreal dilation, and compression drainage. The pore water pressure increases nonlinearly and has a positive correlation with the normal displacement. When the shear distance reaches 100 m, the pore water pressure increases to more than 50% of the total normal stress. Sliding zone liquefaction caused by particle breakage is the main reason for the reduction in shear strength, leading to shear strength decreases by more than 50% and the pore water pressure increases to more than 70% of the total normal stress. The formation process of the Luanshibao landslide can be summarized as follows: seismic activity triggered high-speed sliding initiation, landslide body fragmentation formed a debris flow, sliding zone liquefaction facilitated long runout movement, and debris flow slowed and accumulated. The research findings could provide a reference for the analysis of the mechanisms of high-altitude and long-runout landslides with water saturated loose layers in their movement paths.
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图 1 乱石包高位远程滑坡区域位置与发育特征
a. 乱石包滑坡区域位置；b. 乱石包高位远程滑坡发育特征；c. 崩滑源区照片（镜向EW）；d. 堆积区前缘（镜向SW）
Fig. 1. Location map and development characteristics of the Luanshibao high-altitude and long runout landslide
图 3 ICL-2高速动态环剪仪
a. ICL-2环剪仪主要组成；b. 环剪单元主要组成；c. 剪切盒主要构成
Fig. 3. ICL-2 high-speed ring shear apparatus
图 4 不同法向应力下剪切结果曲线
a. 法向应力200 kPa剪切曲线；b. 法向应力200 kPa剪切试样特征；c. 法向应力400 kPa剪切曲线；d.法向应力400 kPa剪切试样特征；e. 法向应力600 kPa剪切曲线f. 法向应力600 kPa剪切试样特征
Fig. 4. Shear result curves under different normal stresses
图 5 不同法向应力下试样剪切强度参数分析
a. 法向应力200 kPa下应力路径；b. 法向应力400 kPa下应力路径；c. 法向应力600 kPa下应力路径；d. 剪切强度参数拟合
Fig. 5. Analysis of shear strength parameters for samples under different normal stresses
图 6 环剪试样剪切分层特征
a. 法向应力200 kPa下试样剪切特征；b. 法向应力600 kPa下剪切带分层特征；c. 法向应力400 kPa下剪切带分层特征
Fig. 6. Shear layering characteristics of the ring shear test samples
图 7 环剪试验前后颗粒破碎特征
a. 环剪试验前后颗粒粒径对比；b. 主剪切带与非主剪切带对比；c. 不同法向应力下颗粒破碎程度对比；d. 法向应力600 kPa下剪切发育特征
Fig. 7. Characteristics of particle breakage characteristics before and after the ring shear test
图 8 环剪试验中滑动剪切带演化过程和力学特性曲线
Fig. 8. The evolution process of sliding zone and mechanical property curves in ring shear test
图 9 乱石包滑坡远程运动模式
a. 乱石包滑坡远程运动过程；b. 乱石包滑带剖面（镜向SE）
Fig. 9. Long runout mechanisms of the Luanshidabao landslide
表 1 乱石包滑坡高速环剪试验方案
Table 1. The experimental scheme for high-speed ring shear testing of the Luanshibao landslide
样品编号 试验工况 剪切距离(m) 法向应力(kPa) 剪切速度(cm/s) 采样频率(Hz) 颗粒分析 破坏形态分析 LSB⁃S1 高速(50 cm/s)饱和不排水 300 200 50 5 筛分环剪前后试样 高清相机拍照取样 LSB⁃S2 400 LSB⁃S3 600 
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表 2 乱石包滑坡高速环剪试样强度参数统计
Table 2. Statistical analysis of strength parameters for high-speed ring shear samples of the Luanshibao landslide
试样编号 BD 法向应力(kPa) 峰值剪应力(kPa) 残余剪应力(kPa) 残余孔隙水压力(kPa) 峰值内摩擦角(°) 残余内摩擦角(°) LSB⁃S1 0.96 200 184 85 145 42.6 23.6 LSB⁃S2 0.95 400 336 158 312 40.0 21.3 LSB⁃S3 0.95 600 515 195 434 40.6 17.5
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表 3 环剪试验试样破碎特征
Table 3. Breakage characteristics of the ring shear test samples
样品编号 法向应力(kPa) 最大法向压缩厚度(mm) 压缩百分比(%) 颗粒破碎率Bg(%) 中值粒径d50(mm) LSB⁃S1 200 2.73 6.83 80.4 0.33 LSB⁃S2 400 2.90 7.25 85.2 0.32 LSB⁃S3 600 2.93 7.33 95.5 0.30
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