含软弱夹层斜坡地震动力响应过程的边际谱特征研究

Marginal spectrum characteristics of the rock slope with a soft interlayer during an earthquake

地震波的频率特性是地震动的最重要特征之一,斜坡的地震动力响应是地震波各频率组分对斜坡体共同作用的结果。依托于含水平厚软弱夹层斜坡的大型振动台模型试验,着重分析了该斜坡在天然随机波(2008年汶川波)作用下的水平向加速度响应频谱特征。首先,基于Hilbert-Huang频谱变换,对所有原始数据进行了有效的降噪处理,并获得了重构数据的Hilbert边际谱。接着,开展了坡表水平向加速度边际谱在不同高程处和不同激振强度下的变化特征分析,并将频谱特征与时域峰值加速度(PHA)响应和斜坡的宏观变形破坏特征进行对比分析。结果表明:(1)随着高程增加,边际谱幅值也相应增加且谱线出现多个波峰。坡体上部尤其是坡肩是地震作用的敏感部位,随着激振强度增加,加速度波的震动能量从一开始集中在2个频段(即7～11 Hz和15～20 Hz,高频)逐渐向1个频段(7～11 Hz,低频)变化;(2)在激振强度为0.2g～0.5g时,第一卓越频率(最大谱峰值对应的频率)和第二卓越频率(次大谱峰值对应的频率)在数值上呈大幅度、无规律的波动,预示在该震动阶段,坡体结构内部正在经历一个较大的变化(恶化),但未出现宏观变形;(3)时域峰值加速度随高程和激振强度增加的变化规律与最大谱峰值的变化规律较接近,但局部变化受次大谱峰值响应的影响明显;(4)在低频区(<5 Hz),在软弱夹层及其周围(相对高程0.25～0.75)出现了明显的响应低值区,且边际谱的形状和数值在该部位呈无规律性变化;(5)斜坡的变形破坏过程明显受坡表而非坡顶变形的控制,其应存在使得一个地震波与坡体相互作用效应最大的共振高程,该高程范围与以第二卓越频率(16 Hz)作为共振频率所估算的高程较为吻合。

The frequency of seismic waves is one of the most important features of ground motion,and the seismic response of the slope under an earthquake is the combined effect of different frequency components of seismic waves on the slope body.The large-scale shaking table tests were conducted on a slope with the horizontal soft interlayer,and the corresponding response spectrum characteristics of horizontal acceleration were analyzed when the slope was subjected to the natural wave(2008 Wenchuan wave)excitations.Firstly,based on the Hilbert-Huang transform method,the original wave data was efficiently denoised and the Hilbert marginal spectrums were obtained using the reconstructed data.According to the marginal spectrums,the horizontal acceleration responses on the slope surface were analyzed in the frequency domain with different elevations and excitation intensities,respectively.Meanwhile,the peak horizontal acceleration response in the time domain were compared with the macro deformation and failure features of the slope.The research results showed that 1)with the increasing elevation,the spectrum amplitude increased accordingly and multiple peaks occurred in the spectral line.The upper part of the slope,especially the slope crest,was very sensitive to the shaking action.With the increasing excitation intensity,the distribution of the concentrated shaking energy gradually changed from two ranges(ie.7-11 Hz and 15-20 Hz,high frequency)to one range(ie.7-11 Hz,low frequency).2)when the excitation intensity increased from 0.2 g to 0.5 g,both the first and the second dominant frequencies(separately corresponding to the first largest and the second largest spectrum amplitude)demonstrated irregular fluctuations within a wide zone.This indicates there was a deterioration of the inner slope structure during this loading phase,but without the macroscopic deformation.3)with the increasing elevation and the excitation intensity,the change law of the peak horizontal acceleration was similar to the change law of the first largest spectrum amplitude,but locally influenced by the second largest spectrum amplitude response.4)in the low frequency(<5 Hz)range,an obvious weak response zone appeared in and around the soft interlayer(relative elevation is 0.25-0.75).Moreover,the shape and value of the spectrums irregularly varied in the zone.5)the deformation and failure process was clearly controlled by the slope surface rather than the slope crest.A‘resonance elevation’should exist where makes the maximum response occur due to the interaction effect of the seismic waves and the slope body.Besides,this elevation is consistent with the estimated one by using the second dominant frequency(16 Hz)as the resonance frequency.