强震下紫坪铺坝前大型古滑坡体变形破坏效应

为探究512汶川地震中几乎所有大型古滑坡堆积体均保持整体稳定，只在局部坡度较陡及陡缓交界处发生滑塌的变形机制，以紫坪铺水利枢纽坝前左岸灯盏坪大型古滑坡堆积体为例，通过现场深孔监测资料及室内数值模拟分析了堆积体地震变形特征及应力应变分布情况.研究表明，灯盏坪古滑坡堆积体位移最大值出现于地表坡缘处，达150 mm；地震主要影响堆积体剪应力分布，造成灯盏坪前缘下部软化带内剪应力集中；基覆界面及微地貌是控制古滑坡体地震变形破坏模式的主导因素，并非所有古滑坡体均会被地震诱发整体复活，灯盏坪堆积体总体地形坡度为20左右，基覆界面倾角为13左右，地震不会触发其整体失稳，只在局部地形陡缓交界处及转折端发生变形破坏. 

Deformation and Failure Mechanism of Large Ancient Landslide Induced by Wenchuan Earthquake in Front of Zipingpu Hydraulic Dam

To make clear why nearly all large ancient landslides kept stable in Wenchuan earthquake, except for the collapse and deformation of steep slope areas and the boundary of the steep and gentle slope areas, a large ancient landslide was explored, which locates at the left riverbank in front of the dam of Zipingpu. Based on the monitoring data and numerical simulation, the deformation characteristics as well as the strain and stress distribution of the talus slope were analyzed. The results indicate that the maximum displacement of the slope under the earthquake reaches 150 mm, which locates on the shoulder surface of Dengzhanping plateau. The earthquake has a significant influence on shear stress in the ancient landslide, resulting in the stress concentration on the sliding surface in the vicinity of free surface in the front of the Dengzhanping plateau. The deformation and failure mode of the large ancient landslide largely depends on the surface condition between rock bed and overlying talus and the micro-landform. When the overall topographic gradient of the Dengzhanping ancient landslide is 20, and the inclination of rock-soil boundary is about 13, Wenchuan earthquake only led to collapse on the boundary of the steep and gentle slope areas, but not induced the overall instability of the ancient landslide.