Shaking table tests on sliding characteristics and mechanism of liquefaction landslide of low-angle loess deposit in Shibeiyuan
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摘要: 在野外调查、勘探与室内试验的基础上，通过振动台模型试验对1920年海原地震宁夏石碑塬低角度液化滑移启动机理、地貌形成特征、失稳过程及其滑动机制进行研究。结果表明：石碑塬低角度液化滑移是1920年海源地震在特殊地层结构及高烈度地震动共同作用下产生的饱和砂质黄土地层的液化滑移；液化滑移过程包括液化启动、抛射加速、滑移堆积等3个阶段，液化滑移具有高速和长距离流动特性；试验结果表明液化启动是大规模滑移的触发机制；高峰值的地震加速度放大及惯性抛射是液化滑移高速远程的驱动机制；特殊的下部隔水层和中部饱和砂质黄土层的地层结构是大规模低角度滑移形成的物理基础；液化程度的差异造成不同层位土体的运移速度差及拉张推挤作用是形成峰谷相间波浪起伏地貌的原因。研究结果对强震作用下低角度黄土地层地震液化滑移灾害机理的认知与该类滑坡灾害防治技术方法的创新具有重要的参考验证价值。Abstract: Based on the field investigation, exploration and laboratory tests, the initiation mechanism of low-angle liquefaction sliding, geomorphologic formation characteristics, instability process and sliding mechanism of Shibeiyuan in Ningxia during the 1920 Haiyuan earthquake are studied by shaking table model tests. The results show that the low-angle liquefaction sliding of Shibeiyuan is the liquefaction one of the saturated sandy loess formation caused by the special stratum structure and high-intensity ground motion of the 1920 Haiyuan earthquake. The liquefaction sliding process includes three stages: initiation of liquefaction stage, ejected acceleration stage, flow slipping and accumulation stage. Finally, the liquefaction sliding is characterized by high-speed and long-distance flows. The results show that the initiation of liquefaction is the trigger mechanism of large-scale sliding. The seismic acceleration amplification at the peak value and the inertial ejection are the driving mechanism of liquefaction sliding at high speed and long distance. The special stratigraphic structure of the lower permeability aquifer at the bottom and the saturated sandy loess layer in the middle is the physical basis for the formation of large-scale liquefaction sliding with low angle. The difference of liquefied degree leads to that of transport velocity of soils in different layers and the stretching and pushing action, which is the reason for the wavy geomorphology with peaks and valleys. The research results have important reference value for the recognition of earthquake liquefaction and sliding disaster mechanism of low-angle loess stratum under strong earthquakes and the innovation of landslide prevention and control technology.
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Keywords:
- Shibeiyuan /
- seismic liquefaction /
- sliding characteristic /
- sliding mechanism /
- shaking table test
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致谢: 感谢中国地震局兰州地震研究所王谦副研究员、钟秀梅副研究员以及兰州大学马为功博士为本试验给予的支持和帮助。
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图 2 南滑移区现存地貌、钻孔及探槽位置
Figure 2. Existing landforms, boreholes and trial trench in south sliding zone
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图 5 石碑塬原始地层剖面简化模型
Figure 5. Simplified model for profile of original strata in Shibeiyuan
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图 9 100~300 gal加振后模型水位线、液化及变形
Figure 9. Water levels, liquefaction and deformations of model after vibration of 100~300 gal
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图 10 400~600 gal加振后模型水位线、局部液化、运移及变形
Figure 10. Water levels, local liquefaction, migration and deformations of model after vibration of 400~600 gal
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图 11 800 gal加振后模型水位线、液化层运移及变形特征
Figure 11. Water levels, migration and deformation characteristics of liquefied layer after vibration of 800 gal
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图 12 1200 gal加振后模型水位线、液化层整体运移及变形破坏特征
Figure 12. Water levels, migration and deformations and failure characteristics of liquefied layer after vibration of 1200 gal
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图 13 模型液化滑移后特征对比
Figure 13. Comparison of characteristics of model after liquefaction sliding failure
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图 14 初始液化阶段模型坡体内加速度和孔隙水压力发展趋势
Figure 14. Development trend of acceleration and pore-water pressure of model slope at initial liquefaction stage
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图 15 液化滑移启动阶段模型坡体内加速度和孔隙水压力发展趋势
Figure 15. Development trend of acceleration and pore-water pressure of model slope at start liquefaction slip stage
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图 16 1200 gal加载后模型液化流滑及破坏后特征
Figure 16. Sliding and failure characteristics of liquefaction flow of model after loading of 1200 gal
表 1 石碑塬液化地层及其液化判别结果
Table 1 Distribution of liquefied strata and discriminant results of Shibeiyuan
地层类型 土层厚度/m 土层描述 剪切波速/(m·s-1) 取样深度/m 液化临界剪切波速/(m·s-1)(液化判别结果[6]) Ⅶ Ⅷ Ⅸ 上部黄土层 12~16 黄褐色、次密、较均匀，岩心成短柱状 151 6.5 — — 151 第一古土壤层 1.4~2.0 红褐色、硬塑状、中密、具层理 211 10.5 68(否) 94(否) 135(否) 砂质黄土层 5.1~11.7 黄褐色、中湿、土层较均匀 188 15 98(否) 136(否) 196(是) 第二古土壤层 0.9~6.0 红褐色、硬塑、中密、较湿 244 35.5 118(否) 163(否) 236(否) Q2古土壤层 11.4~21.2 褐色、软塑、稍密、具缩孔现象 272 40 122(否) 169(否) 244(否) 
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表 2 不同土层试样的基本物性指标及颗粒组成
Table 2 Basic physical property indexes and particle composition of samples from different strata
地层土样 取样深度/m 干密度/(g·cm-3) 含水率w/% 孔隙比 饱和度Sr/% 颗粒组成/% 黏粒 粉粒 砂粒 上部非饱和黄土层（Q3、Q4） 6.5 1.35 5.51 1.12 13.36 13.15 77.99 8.86 第一古土壤层（Q3） 13.5 1.68 11.14 0.79 38.08 16.97 81.01 2.02 饱和砂质黄土层（Q3） 16.5 1.65 27.69 1.09 75.40 12.20 59.66 28.14 Q2古土壤层（Q2） 35.5 1.72 26.82 1.00 72.82 13.22 66.21 20.57
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表 3 试验加载序列
Table 3 Loading sequences for tests
序号 加载波形 激振方向 烈度 设计输入振幅/gal 实际加载幅值/gal 1 正弦扫频 水平（x） — 50 2 汶川地震记录波 水平（x） Ⅶ度 100 95 3 汶川地震记录波 水平（x） Ⅷ度 200 185 4 汶川地震记录波 水平（x） Ⅷ度 300 290 5 汶川地震记录波 水平（x） Ⅸ度 400 385 6 汶川地震记录波 水平（x） Ⅸ度 600 626 7 汶川地震记录波 水平（x） Ⅸ度 800 825 8 正弦扫频 水平（x） — 50 9 汶川地震记录波 水平（x） Ⅹ度 1200 1154
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