层状复合岩体边坡动力特性及地震响应特性的振动台试验研究

Shaking table test of dynamic responses of a layered complex rock slope under earthquake

层状复合岩体边坡往往具有复杂的岩性组合及岩体结构特征。人们对这一类边坡在地震作用下的动力响应特性及滑坡灾害成因机制仍缺乏深入的认识。以2008年"5·12"汶川地震在层状复合岩体边坡内诱发的一处典型岩质滑坡为原型,以原始边坡的地形和地层结构为模拟内容,并采用滑坡区邻近地震台实测加速度波作为边坡底部激励,完成层状复合岩体边坡地震动力响应特性的小型振动台试验研究。基于传感器测得数据,分析模型边坡的固有频率特征和加速度响应特征,并比较水平向和竖直向响应之间的差异。与此同时,本文还着重分析模型边坡中碳质板岩薄弱层的加速度响应和位移响应特征,以观察其在层状复合岩体边坡响应中所起的作用。主要研究结果表明:(1)模型边坡在分别受到水平向和竖直向地震波激振时,将表现出不同的振动形态。2个方向上的固有频率都经历了三阶段变化过程,在这一过程中,固有频率呈现出总体下降的趋势,表明结构在不断恶化。(2)模型边坡竖直向加速度的高程放大效应弱于水平向加速度,但模型边坡对竖直向输入波的改造作用更明显。碳质板岩层对竖直向加速度表现出了明显的削弱作用。(3)碳质板岩层在激振强度增大时出现鼓胀变形。在开展破坏性试验阶段,碳质板岩层的水平位移峰值超过上部的千枚状板岩层。然而,在本试验条件下,这种岩层间的非协调变形并没有导致模型边坡最终沿着碳质板岩层发生破坏,这与现场观察到的原型滑坡实际滑移面位置有出入。尽管如此,该研究成果,尤其是其所揭示的水平向和竖直向响应差异以及岩层间的响应差异仍然可为层状复合岩体边坡的地震成灾机制解释提供一定参考。

A layered complex rock slope always consists of complex lithology and rock structure,and its seismic responses and landslide formation mechanisms are not completely understood. In the present study,a small-scale shaking table test was carried out on a layered complex rock slope model,taking a typical landslide triggered by the 2008"5·12"Wenchuan earthquake as the prototype slope,simulating the original topography and rock strata and using the accelerations recorded at the seismic station adjacent to the landslide area as input waves. Based on the sensor measurements,the natural frequencies and acceleration responses of the model slope were analyzed,and the horizontal and vertical responses were compared. In addition,the acceleration and displacement responses of the weak layer in the model slope,namely carbonaceous slate,were analyzed to emphasize the role of the layer in the whole slope’s responses. The main results show that the model slope demonstrates different vibration modes under horizontal and vertical excitations,and the natural frequencies for both directions undergo three-phase decreasing process which indicates a gradual deterioration of the slope structure. The topographic amplification effect of the vertical acceleration of the model slope is weaker than that of the horizontal acceleration. However,the model slope shows a more significant modification effect on the vertical input waves,and the carbonaceous slate plays a weakening effect of the vertical acceleration. Bulging deformation was observed on the surface of the carbonaceous slate under a high level of excitation. At the stage of the destructive test,the peak horizontal displacement in the carbonaceous slate is larger than that in the overlying phyllite slate. However,the incompatible deformation among different strata does not cause the model slope to slide along the carbonaceous slate,which is inconsistent with the actual location of the sliding surface of the prototype landslide. Nonetheless,the above results,especially the differential responses between the horizontal and vertical accelerations and between different strata,can still help to explain the failure mechanism of a layered complex rock slope triggered by an earthquake.