不同失稳形态黄土边坡的动力响应研究

Study on Dynamic Response of Loess Slopes with Different Failure Patterns

针对傅里叶变换的不足,为反映地震波时域和频域的局部特性,引入小波包变换分析方法,通过两台不同坡度的黄土边坡模型振动台试验,对加速度响应信号进行小波包变换,对比研究峰值加速度(PGA)在边坡地震失稳过程中的变化特征,观察分析失稳过程。结果表明:黄土边坡坡度的陡缓差别,会对边坡地震失稳形态产生影响,陡坡为突发型,缓坡为渐进型。突发型失稳边坡的地震失稳过程可划分为破坏前、极限状态和破坏后三个阶段,而渐进型边坡的失稳过程可划分为弹性变形、塑性小变形和大变形失稳破坏三个阶段。对地震响应小波包变换分析显示,边坡动力失稳过程中起主要作用的是地震波的低频部分(0.10~12.51 Hz),其中第一频段(0.10~6.25 Hz)始终是主频,第二频段(6.26~12.51 Hz)始终是次频。边坡第一频段的能量占比E_(1)和第二频段的能量占比E_(2)的高程规律的改变,可作为判断边坡地震变形损伤情况产生变化的依据。反应谱曲线幅值和特征周期的突变证明了前述分析的正确性。

In response to the shortcomings of Fourier transform,in order to reflect the local characteristics of seismic wave in time domain and frequency domain,the wavelet packet transform was introduced to analyze the acceleration response signal through shaking table tests of two loess slope models with different slopes,and to study the development trend and characteristics of peak ground acceleration(PGA)in the process of slope instability evolution.The results show that due to the properties of different gradients of the loess slope,the failure pattern of the steep slope can be described as“abrupt failure type”,while the failure pattern of the gentle slope is“progressive failure type”.The seismic failure process of“abrupt failure type”slope can be divided into three stages including pre-failure,ultimate state failure and post-failure,while that of“progressive failure type”slope can be divided into three stages including elastic deformation,small plastic deformation and large deformation failure.The wavelet packet transform analysis of seismic response shows that seismic waves of low frequency components(0.10~12.51 Hz)play a major role in the failure process of slopes,with the first frequency band(0.10~6.25 Hz)as always the main frequency,while the second frequency band(6.26~12.51 Hz)as always the secondary frequency.The change of elevation law of the energy proportion E_(1) of the first frequency band and the energy proportion E_(2) of the second frequency band can be used as the basis for judging the change of slope seismic deformation and damage.The changes of the amplitude and characteristic period of response spectrum prove the correctness of the foregoing analysis.