Analysis of Ground Motion Characteristics of Typical Slope Terrain
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摘要: 以云南鲁甸6.5级地震中房屋建筑破坏严重的龙头山集镇斜坡地形为例，通过地脉动测试分析得出斜坡及坡顶测点相对于坡脚参考点谱比峰值均＞1，顺坡向谱比峰值大于垂直坡向谱比峰值，且谱比峰值从斜坡坡脚到坡顶逐渐增大，坡顶处约为3；顺坡向谱比峰值对应的频率为4.57～5.39 Hz，垂直坡向谱比峰值对应的频率稍高，为5.42～5.96 Hz。通过结合黏弹性边界的时域动力有限元方法分析斜坡地形在垂直入射地震动作用下的响应，数值模拟结果表明，斜坡坡顶处的位移放大作用显著，坡脚处放大作用较小；介质剪切波速对斜坡地震动的影响较明显，尤其是坡顶点处不同介质剪切波速模型位移峰值差异较大。由于斜坡地形复杂的散射效应，在斜坡及附近测点均出现明显的转换面波，坡顶点处波形转换最显著。数值模拟结果进一步验证了龙头山集镇依坡而建的房屋建筑破坏严重是由局部地形地震动放大效应与地震动差动共同作用引起的。Abstract: Taking the slope topography of Longtoushan market town, which was seriously damaged in the MS6.5 earthquake in Ludian, Yunnan Province, as an example, through the analysis of ground pulsation test, it is found that the peak spectral ratio of the slope and the measuring point at the slope top relative to the reference point at the slope toe is > 1, the peak spectral ratio in the slope direction is greater than that in the vertical slope direction, and the peak spectral ratio gradually increases from the slope toe to the slope top, and the peak spectral ratio at the slope top is about 3; The frequency corresponding to the peak value of the slope direction spectrum is 4.57 ~ 5.39 Hz, and the frequency corresponding to the peak value of the vertical slope direction spectrum is slightly higher, 5.42 ~ 5.96 Hz. The time domain dynamic finite element method combined with viscoelastic boundary is used to analyze the response of slope terrain under vertical incident ground motion. The numerical simulation results show that the displacement amplification at the top of slope is significant, and the amplification at the foot of slope is small; The influence of medium shear wave velocity on the ground motion of slope is obvious, especially the displacement peak value of different medium shear wave velocity models at the top of slope is different. Due to the complex scattering effect of the slope topography, there are obvious converted surface waves at the slope and nearby observation points, and the waveform conversion at the top of the slope is the most significant. The numerical simulation results further verify that the serious damage of the buildings built along the slope in Longtoushan market town is caused by the combined effect of local terrain ground motion amplification and seismic differential.
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Key words:
- Slope topography /
- Surface wave /
- Shear wave velocity /
- Scattering effect /
- Seismic response /
- Finite element analysis
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图 2 斜坡地形剖面及测点布置示意（单位：米）
Figure 2. Schematic diagram of slope topographic profile and observation point location（Unit：m）
图 4 斜坡模型及测点布置示意（单位：米）
Figure 4. Schematic diagram of slope model and observation point location（Unit：m）
图 5 斜坡二维有限元分析模型
Figure 5. Schematic diagram of 2D finite element analysis model of slope
图 6 输入脉冲地震动及其傅里叶振幅谱
Figure 6. Input pulse ground motion and its Fourier amplitude spectrum
图 10 测点质点运动轨迹（单位：米）
Figure 10. Particle trajectory diagram of each observation point（Unit：m）
表 1 斜坡测点及坡顶测点相对于坡脚测点地脉动谱比
Table 1. Spectral ratio results of measuring points relative to slope
测点编号 方向 谱比卓越频率/Hz 谱比峰值 P2 垂直坡向 5.96 1.01 顺坡向 4.57 1.03 P3 垂直坡向 5.79 1.04 顺坡向 4.85 1.33 P4 垂直坡向 5.66 1.20 顺坡向 5.36 1.83 P5 垂直坡向 5.81 1.76 顺坡向 4.89 2.33 P6 垂直坡向 5.42 2.83 顺坡向 5.39 3.01 
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