汶川地震大光包滑坡动力响应特征研究

DYNAMIC RESPONSE CHARACTERISTICS OF DAGUANGBAO LANDSLIDE TRIGGERED BY WENCHUAN EARTHQUAKE

运用FLAC3D模拟大光包滑坡变形失稳特征,并输入距离滑坡约4.3 km的清平台站强震加速度三向记录,结果表明:其地震动力响应较为复杂,受控于斜坡形态、岩体(地质)结构及地震强度和振动持时等因素,在水平加速度响应方面,前缘滑坡更为明显,地震动频率更高,振幅更大,利于前缘的顺层失稳滑动;在竖向加速度响应方面,后缘滑体的振幅更大,竖向加速度(绝对值)数倍于水平加速度,利于拉裂、振碎解体和抛掷失稳。大光包滑坡与简单均值结构的边坡地震动力响应特征不完全一致,随高程、坡度放大的趋向性和节律性不明显。结合地震动力响应和运动特征,对滑坡堆积和滑源进行概化分区:(1)下部顺层滑坡堆积区,是滑坡的主堆积区,分布于滑坡东侧,堵塞黄洞子沟;(2)上部崩滑堆积区,分布于滑坡西北、北侧,具有明显的带状特征;(3)后缘陡壁及倒石堆区,侧缘拉裂边界,近直立不规则凹凸状断壁,分布多组张拉裂隙,说明受陡倾角张性裂隙控制,表现为张性破坏特征,陡崖下部分布大量倒石堆,呈串珠状分布,以碎块石为主,岩性与后缘及北侧陡壁岩体一致,系地震后的重力调整所致;(4)顺层滑面及擦痕区,在滑面上分布大量与岩层倾向相同的擦痕,说明顺层滑坡在后部具有向北方向偏转滑动的特征。

The complicate earthquake dynamic response is simulated with FLAC3D that is much different with simple/homogeneous slope due to poor amplitude effect along the height. For the horizontal acceleration response, the front of the landslide has greater vibrating frequency and amplitude, that is easier to trigger the slide along the inclined layer. For the vertical acceleration response, the back of the landslide has greater amplitude of vibration, and as three times as the absolute value of the acceleration in the front, that is easier cracking, fragmenting or even throwing rock mass. In light of the earthquake dynamic response and movement, the landslide accumulation and source are zoned as follows： （1） the lower inclined bedding sliding accumulation, which distributed in the East and dammed a tributary named the Huangdongzi; （2） the upper avalanche accumulation, which distributed in the Northwest and the North that overlay the North margin of previous sliding accumulation with belt-like; （3） the back cliff and talus, in which lots of cracks in the cliffs shows the tensive failures during the vibration;and lots of talus masses show gravity processes after the earthquake;（4） inclined bedding sliding surface and striation, which distributed at the back of the lower inclined bedding landslide. Enormous large-scale striation belts show the moving direction to North that is as same as the tendency of the layer.