斜坡加速度动力响应特性的大型振动台试验研究

以"5·12"汶川地震灾区典型斜坡为原型,采用水平层状上硬下软和上软下硬2种岩性组合概念模型,设计并完成比例1:100的大型振动台试验。在满足相似律的条件下,通过输入不同地震波类型、频率、激振方向和振幅,系统地研究模型斜坡的地震动力响应特性。以输入加速度峰值0.3g为例,分析不同岩性组合模型斜坡在单向天然地震波作用下的同向加速度动力响应规律,研究结果表明,加速度沿竖直和水平方向的响应都呈现明显的非线性特征;总体上,高程对地震波具有明显的放大效应。在水平向地震波作用下,斜坡的动力响应主要出现在斜坡的中上段,而在同等强度的激振力作用下,竖直向加速度最大放大倍数仅相当于水平向加速度最大放大倍数的1/2左右,且动力响应较强部位主要出现在斜坡的中下段。不同岩性组合结构对加速度响应规律的影响也因激振方向不同而异,在水平向地震波作用下,上硬下软组合斜坡总体上要比上软下硬组合斜坡对加速度的放大程度大,在竖直向地震波作用下则相反。通过对比坡面不同高程处的加速度傅里叶谱表明,在地震波从下往上传播过程中,上硬下软斜坡对起放大作用的频段具有明显的选择性,竖直向激振条件下对2种岩性组合斜坡加速度起放大作用的卓越频率比水平向激振条件下的卓越频率大得多。

LARGE-SCALE SHAKING TABLE TEST STUDY OF ACCELERATION DYNAMIC RESPONSES CHARACTERISTICS OF SLOPES

Based on prototype slopes in disaster areas of‘May 12’Wenchuan earthquake，two types of horizontally layered model slopes including hardness-upward and softness-upward are designed to perform the large-scale shaking table test with the geometric scale of 1∶100. Under the condition of similitude law，the seismic responses of model slopes are investigated with different input wave kinds，frequencies，excitation directions and amplitudes. Taking the situations of inputting acceleration amplitude of 0.3g as the typical example，the co-rotating acceleration dynamic responses of model slope with different lithology associations are analyzed under the single crude seismic load. The results show that the responses present obvious non-linearity along vertical and horizontal directions；and the elevation has amplification effect on seismic waves totally. Under the horizontal seismic load，the dynamic responses of slope appears mainly at the middle-upper part. However，with the equal input seismic load，the largest amplification of vertical acceleration is only one half of that of the horizontal acceleration；and the dynamic responses of slope appears mainly at the middle-lower part. The effects of different lithology associations on the acceleration response rules also vary with the different excitation directions. That is，under the horizontal seismic load，the hardness-upward slope demonstrates larger amplification effect of acceleration than the softness-upward slope basically；and under the vertical load，the result is opposite. Finally，by comparison of acceleration Fourier spectra in different elevations on the slope surface，the hardness-upward slope has obvious selectivity of predominant frequencies while the waves are propagating from the bottom；and for both model slopes，the predominant frequencies in vertical excitation concentrate on higher frequency ranges than those in horizontal excitation.