石碑塬低角度黄土地层液化滑移特征与机理振动台试验研究

Shaking table tests on sliding characteristics and mechanism of liquefaction landslide of low-angle loess deposit in Shibeiyuan

在野外调查、勘探与室内试验的基础上,通过振动台模型试验对1920年海原地震宁夏石碑塬低角度液化滑移启动机理、地貌形成特征、失稳过程及其滑动机制进行研究。结果表明:石碑塬低角度液化滑移是1920年海源地震在特殊地层结构及高烈度地震动共同作用下产生的饱和砂质黄土地层的液化滑移;液化滑移过程包括液化启动、抛射加速、滑移堆积等3个阶段,液化滑移具有高速和长距离流动特性;试验结果表明液化启动是大规模滑移的触发机制;高峰值的地震加速度放大及惯性抛射是液化滑移高速远程的驱动机制;特殊的下部隔水层和中部饱和砂质黄土层的地层结构是大规模低角度滑移形成的物理基础;液化程度的差异造成不同层位土体的运移速度差及拉张推挤作用是形成峰谷相间波浪起伏地貌的原因。研究结果对强震作用下低角度黄土地层地震液化滑移灾害机理的认知与该类滑坡灾害防治技术方法的创新具有重要的参考验证价值。

Based on the field investigation,exploration and laboratory tests,the initiation mechanism of low-angle liquefaction sliding,geomorphologic formation characteristics,instability process and sliding mechanism of Shibeiyuan in Ningxia during the 1920 Haiyuan earthquake are studied by shaking table model tests.The results show that the low-angle liquefaction sliding of Shibeiyuan is the liquefaction one of the saturated sandy loess formation caused by the special stratum structure and high-intensity ground motion of the 1920 Haiyuan earthquake.The liquefaction sliding process includes three stages:initiation of liquefaction stage,ejected acceleration stage,flow slipping and accumulation stage.Finally,the liquefaction sliding is characterized by high-speed and long-distance flows.The results show that the initiation of liquefaction is the trigger mechanism of large-scale sliding.The seismic acceleration amplification at the peak value and the inertial ejection are the driving mechanism of liquefaction sliding at high speed and long distance.The special stratigraphic structure of the lower permeability aquifer at the bottom and the saturated sandy loess layer in the middle is the physical basis for the formation of large-scale liquefaction sliding with low angle.The difference of liquefied degree leads to that of transport velocity of soils in different layers and the stretching and pushing action,which is the reason for the wavy geomorphology with peaks and valleys.The research results have important reference value for the recognition of earthquake liquefaction and sliding disaster mechanism of low-angle loess stratum under strong earthquakes and the innovation of landslide prevention and control technology.