An analysis of dynamic response characteristics of the Yigong Landslide in Tibet under strong earthquake
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摘要: 西藏雅鲁藏布江大峡谷地区是地震滑坡的高易发区，发生过多期地震滑坡。以西藏易贡滑坡为例，运用FLAC3D有限差分方法，对滑坡所在山体进行频响特征分析，并以此为基础对其地震波作用下的放大效应开展研究，最后对近场强震条件下山顶潜在崩滑体稳定性进行预测。研究结果发现：易贡山体整体卓越频率处于较低值，山顶卓越频率主要集中在1 Hz以下、山顶两侧卓越频率在2~6 Hz之间；在地震波作用下，易贡山体顶部及两侧出现不同程度放大，山体内部沿高度向上呈先增后减、进而再次增大的变化趋势，其计算结果与频响特征分析结果基本一致；静力条件下，潜在崩滑体基本保持稳定，其安全系数为1.27，但地震作用下的计算结果却表明其发生了失稳破坏；在考虑水平向和竖向加速度同时输入的近场强震条件下，崩滑体稳定程度将进一步下降，因此需加强近场强震条件下山体的风险分析及预测。Abstract: The Yarlung Zangbo River Grand Canyon area in Tibet is a highly prone area for earthquake-triggered landslides,where several landslides have occurred before. Taking the Yigong Landslide as an example,this article analyzes the frequency response characteristics of the Yigong Mountain by using the FLAC3D finite difference method. Based on the results,the amplification effect of the Yigong Mountain under seismic waves is discussed and the stability of the Yigong Landslide remnant under the condition of near-field strong earthquakes is predicted. Results show that the overall predominant frequency of the Yigong Mountain is at a low value. The predominant frequencies of the mountain top mainly concentrate below 1 Hz,while that of both sides of the mountain top vary from 2~6 Hz. Under the action of seismic waves,the predominant frequencies of the top and both sides of the mountain appear different degrees of amplification,and that in the mountain interior along the height upward shows the change of first increasing then decreasing,and then increasing again. The calculated results are basically identical with the frequency analysis. Stability analysis shows that the Yigong Landslide remnant keeps stable with a safety factor of 1.27 in static condition; however,the results under the earthquake show the occurrence of instability and failure. Finally,it is predicted that the damage of the Yigong Landslide remnant will obviously increase when considering both horizontal and vertical seismic waves. Therefore,it is necessary to strengthen the risk analysis and prediction of mountains under the condition of near-field strong earthquakes.
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Key words:
- strong earthquake /
- Yigong Landslide /
- numerical simulation /
- dynamic response /
- stability analysis
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图 4 不同频率Ricker子波作用下易贡山体水平向加速度云图
Figure 4. Contours of horizontal acceleration of the Yigong Landslide under the action of Ricker wavelet with varying frequencies
图 5 不同频率Ricker子波作用下易贡山体竖向加速度云图
Figure 5. Contours of vertical acceleration of the Yigong Landslide under the action of Ricker wavelet with varying frequencies
图 6 汶川地震卧龙台站实测地震记录
Figure 6. Seismic records of the Wenchuan Earthquake in the Wolong Station
图 7 截取后的卧龙实测地震记录及其傅里叶谱值
Figure 7. Extracted seismic records of the Wolong Station and its Fourier spectrum ratio with power spectrum
图 8 实测地震波作用下易贡山体坡面放大效应
A1、B1—水平向加速度曲线；A2、B2—竖向加速度曲线
Figure 8. Measured amplification effect of the Yigong Mountain surface under earthquake waves(A1, A2: Horizontal and vertical accelerations under EW and UD seismic waves. B1, B2: Horizontal and vertical accelerations under only EW seismic wave.)
图 9 实测地震波作用下易贡山体内部放大效应
Figure 9. Measured amplification effect of the Yigong Mountain interior under earthquake waves(A1, B1: Horizontal acceleration. A2, B2: Vertical acceleration)
图 12 动力加载条件下剪应变增量及塑性区分布图
Figure 12. Shear strain increment and plastic zones distribution under dynamic loading
图 13 两向加速度同时加载条件下残余变形量曲线
Figure 13. Curves of residual deformation under simultaneous loading of both EW and UD seismic waves
图 14 水平向加速度加载条件下残余变形量曲线
Figure 14. Curves of residual deformation under the loading of EW seismic waves
表 1 不同工况下坡体表面典型监测点加速度值
Table 1. Acceleration values of typical monitoring points on the slope surface under varying working conditions
监测点序号 加速度方向 加速度值/(m·s-2)(两向加速度加载) 加速度值/(m·s-2)(水平向加速度加载) A13 水平向 25.1 15.5 竖向 17.8 10.4 A7 水平向 12.0 9.0 竖向 13.7 5.5 B1 水平向 15.8 11.9 竖向 23.5 12.4 B2 水平向 14.8 10.2 竖向 21.0 10.7 
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表 2 不同工况下稳定性计算结果
Table 2. Stability analysis under varying working conditions
指标 静力条件 工况1：水平及竖向加速度输入 工况2：水平向加速度输入 塑性区 未贯通 贯通 贯通 剪应变增量最大值 约0.02 约0.14 约0.08 残余变形量/m 无 B1监测点为最大水平0.8；竖向1.0 B1监测点为最大水平0.3；竖向0.6 稳定性 稳定安全系数1.27 失稳残余变形不收敛 失稳残余变形不收敛
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