强震作用下反倾薄层岩质斜坡倾倒破坏机制及动力响应研究

Dynamic response and failure process of anti-dip rock slope under strong earthquake

反倾岩质边坡在三江并流地区具有广泛的发育和分布,其变形和破坏现象在该区域内所有边坡问题中,尤为突出,地震是诱发滑坡的重要动力因素,常常导致大规模的滑坡灾害。以金沙江左岸宗绒历史性堵江滑坡为例,设计并完成了缩尺相似材料振动台物理模型试验。通过加载不同类型的地震波以及不同频率、幅值,研究反倾薄层岩质斜坡的动力响应和变形破坏机制以及软弱破碎带的影响。试验结果表明,反倾岩质斜坡在强震作用下存在高程放大效应和趋表效应,幅值越大越明显。斜坡加速度放大系数增长速率受频率的影响要高于幅值的影响,在不同幅值下,加速度放大系数最大值出现在0.2 g~0.3g。软弱破碎带的存在改变了斜坡动力响应特征,其厚度对地震波的放大效应存在明显的差异,为厚层段抑制,薄层段放大。幅值0.3g~0.4g为斜坡启裂的临界动力条件,0.7g~0.8g是斜坡失稳破坏的临界动力条件,其破坏过程大致可以分为3个阶段:①形成坡顶张拉裂缝和坡趾剪切裂缝;②裂缝的扩展和浅层块体的剪切破坏滑动-块状倾倒;③斜坡浅层的主滑面的形成,斜坡破坏。

Anti-dip rock slopes have a wide development and distribution in the Sanjiang rivers,and their deformation and damage phenomena are particularly prominent among all slope problems in the region.Earthquake is an important dynamic factor to induce landslides,which often leads to large-scale landslide disasters.In this paper,a model test of a reduced scale similar material shaking table was designed and completed using the historical landslide dam at Zongrong on the left bank of the Jinsha River as an example.By loading different types of seismic waves as well as different frequencies and amplitudes,the dynamic response and deformation damage mechanisms of anti-dip rock slopes and the influence of structural surfaces were investigated.Test results show that there is an elevation amplification effect and skin effect on anti-dip slopes under strong seismic action,the larger the amplitude,the more obvious it is.The rate of increase of the slope acceleration amplification factor is influenced more by frequency than by amplitude.The maximum values of the acceleration amplification factor occur at 0.2 g-0.3g for different amplitude values.The presence of structural surfaces changes the dynamic response characteristics of the slope,and there is a clear difference in the amplification effect of their thickness on seismic waves,as thicker sections are suppressed and thinner sections are amplified.Amplitude 0.3 g-0.4g is the critical dynamic condition for slope cracking and 0.7 g-0.8g is the critical dynamic condition for slope destabilisation damage.The slope damage process can be broadly divided into three stages:①the formation of top-of-slope tension cracks and toe-of-slope shear cracks;②the expansion of cracks and shallow block shear damage sliding-block toppling;③the formation of the main slip surface of the shallow slope and slope damage.