Large Shaking Table Test on Seismic Response of Site with Tilted Interlayer
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摘要: 为了研究含倾斜夹层场地在地震作用下的动力响应及为可能的场地加固提供指导，基于大型振动台模型试验，研究了含倾斜夹层场地在El Centro地震波作用下的加速度、应变及位移响应特征，同时通过频谱分析讨论了夹层对场地稳定性的影响，并用拟静力分析得到场地的启动临界加速度及场地的稳定系数. 试验结果表明：夹层对于加速度峰值存在明显的削弱效果，加载地震波峰值越大，削弱程度越大，同时基岩中加速度放大系数呈现“量级饱和”特征；夹层处应变峰值最大，当加载地震波峰值大于0.33g时，场地平台与斜坡拐角下基覆中存在另一峰值，应变形状呈现“W”形；夹层对20 Hz附近频段的傅里叶幅值有一定的削弱作用，同一土层反应谱卓越周期基本一致，不同土层反应谱差别较大，夹层处（0.31 s）卓越周期大于基岩（0.19 s）与基覆处（0.21 s）；拟静力分析显示0.33g时场地的稳定系数为3.16，强风化带启动的临界加速度为1.42g.Abstract: To investigate the dynamic response of a complex site with a tilted interlayer and provide a potential reinforcement for the site, a large-scale shaking table model test was done to study the acceleration, strain and displacement responses of the site. The effects of the interlayer on the stability of the site are discussed based on an analysis of the Fourier spectrum and response spectrum under the El Centro seismic wave. Furthermore, the critical acceleration and stability factor of the site are obtained through a pseudo-static analysis. Experimental results show that the interlayer obviously weakens the peak acceleration of the seismic wave and that the degree of impairing effects intensifies with the seismic peak acceleration increasing. There is a feature of ‘magnitude saturation’ for the acceleration amplification coefficient (AAC) of the position of bedrock. The peak strain of the interlayer is greater than those of the other layers. When the input earthquake amplitude is larger than 0.33g, there is another peak strain in the cover layer which is located at a platform corner and the strain curve presents a form is ‘W’. The interlayer can also weaken to some extent the amplitude of the Fourier spectrum at about 20 Hz. The predominant periods of theresponse spectra measured from different cross sections of the same soil layer are similar, but obviously different between different soil layers. The predominant period of the interlayer (0.31 s) is greater than those of the bedrock layer (0.19 s) and the cover layer (0.21 s). According to the pseudo-static analysis, when the peak acceleration of the seismic wave loaded is 0.33g, the site stability factor is 3.16, and the critical acceleration of the potential slip area is 1.42g.
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Key words:
- site /
- tilted interlayer /
- dynamic response /
- shaking table test /
- stability
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图 3 试验测点布置示意图及应变带
Figure 3. Monitoring points layout of the completed model and the strip of strain gauge
图 5 II截面、III截面加速度放大系数变化规律
Figure 5. Variations of the AAC in section II and section III
图 6 加速度放大系数随加载波峰值变化规律
Figure 6. Variations of AAC with the increase of loading seismic wave amplitude
图 8 傅里叶谱随加载地震波幅值变化规律
Figure 8. Fourier spectra for different amplitudes of loading seismic wave
图 9 I截面傅里叶谱随高度变化规律
Figure 9. Fourier spectrum change of section I when altitude changes
图 10 不同位置夹层傅里叶谱变化规律
Figure 10. Fourier spectra of interlayer located at different altitudes
表 1 振动台概况
Table 1. Details of the shaking table
参数 取值 自由度 6 尺寸 6 m × 6 m 最大负载/kN 600 最大水平位移/mm ± 150 最大垂直位移/mm ± 100 满载最大水平加速度/（×g） 1 满载最大垂直加速度/（×g） 0.8 空载最大水平加速度/（×g） 3 空载最大垂直加速度/（×g） 2.6 频率范围/Hz 0.1～80.0 
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表 2 模型试验物理量相似常数
Table 2. Physical quantities and similarity constants of the model
序号 物理量 相似关系 相似常数 备注 1 几何尺寸L c1 70 控制量 2 土体密度ρ c2 1 控制量 3 重力加速度g c3 = 1 1 控制量 4 泊松比μ c4 = 1 1 导出量 5 变形模量E c5 = a1 70 导出量 6 内摩擦角φ c6 = 1 1 导出量 7 粘聚力c c7 = a1 5 导出量 8 剪切波速Vs c8 = a10.5 8.37 导出量 9 持续时间T c9 = a10.5 8.37 导出量 10 输入加速度a1 c10 = 1 1 导出量 11 输入振动频率ω c11 = a1–0.5 0.119 导出量 12 响应线位移s c12 = a1 70 导出量 13 响应角位移θ c13 = 1 1 导出量 14 响应应变ε c14 = 1 1 导出量 15 响应速度V c15 = a10.5 8.37 导出量 16 响应应力σ c16 = a1 70 导出量 17 响应加速度a2 c17 = 1 1 导出量
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表 3 模型和原型土体参数
Table 3. Parameters of soil in the model and prototype
土层 类型 ρ/（g•cm–3） E/Pa φ/（°） c/kPa μ 基覆 模型 2.1 3.5 × 104 41 6.00 0.25 原型 2.1 2.5 × 106 40 6.00 0.25 夹层 模型 1.8 3.8 × 103 12 0.75 0.30 原型 1.8 2.7 × 105 21 65.00 0.30 基岩 模型 2.5 7.5 × 104 45 12.00 0.20 原型 2.5 5.5 × 106 45 790.00 0.20
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表 4 不同加载地震波幅值时边坡位移
Table 4. Displacements of slopes under different El Centro seismic wave amplitudes
加载地震
波幅值坡顶1.30 m 坡中1.11 m 坡底0.92 m 峰值 永久 峰值 永久 峰值 永久 0.15g 0.91 – 0.02 0.80 0.01 0.94 – 0.03 0.33g 2.14 – 0.03 1.83 0.01 2.06 – 0.04 0.50g 3.16 – 0.01 2.77 0.02 3.28 – 0.20 0.70g 5.58 – 0.58 4.73 – 0.58 5.37 – 0.51
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