汶川地震诱发罐滩滑坡形成机制初步分析

FAILURE MECHANISM ANALYSIS OF GUANTAN LANDSLIDE INDUCED BY WENCHUAN EARTHQUAKE

安县罐滩滑坡由汶川地震诱发形成,发育于存在软弱基座的反倾斜坡中,体积达468×104m3。罐滩滑坡由"5.12"汶川地震及当晚暴雨诱发形成,发生时间滞后地震8 h,是典型的地震后效型滑坡。滑坡位于龙门山前山断裂带上盘,自然斜坡走向与断裂带近平行,水平距离约400 m,前山断裂带的分支断裂从坡体下部通过,并形成底部泥岩和上部白云岩的分界线。调查和分析表明,下软上硬的坡体结构是滑坡产生的基础,强烈的地质构造活动背景是其产生的重要条件,强烈的地面震动和高强度暴雨是导致产生滑坡的根本因素。滑坡的形成机制和发展过程可以分为以下3个阶段:自然斜坡的压缩-倾倒变形、震后滑面贯通阶段、滑坡整体破坏阶段。滑坡体形成沿河长400 m,纵向长880 m,平面面积1.82×105m2的滑坡堆积体,堵塞雎水河形成罐滩堰塞湖。

Guantan landslide,located on the right side of the Jushui River,at Jushui town,An xian county,Sichuan Province,is generated in the laminated structure slope dipping inward with soft rock at the bottom.It is located in the bedding slope dipping inwards with soft rock at the bottom.Its volume is up to 4.68 million m^3.The landslide is induced by the Wenchuan Earthquake and the storm,and occurred 8 hours after the Wenchuan Earthquake.Guantan landslide is located on the upper plate of the Jiangyou-Guanxian Fault.The orientation of the slope is parallel to the fault with a distance of 400 meters.A branch of the Jiangyou-Guanxian Fault goes through the slope at the lower part,which forms the boundary of dolomite rocks in the upper part and the mudstone in the lower part.According to the engineering geological survey and analysis,the landslide is controlled by three factors： 1） the structure of the slope with soft rock in the bottom and hard rock in the upper part is the basis of landslide,2） strong tectonic movements form crushed rock mass in the slope,and 3） heavy earthquake motion and storm induced the movement of the landslide.The mechanism and process of the landslide can be divided into three stages as follows： 1） the stage of compression and toppling of the slope before the Wenchuan Earthquake,2） the stage of sliding surface developing,and 3） the stage of integral movement of the landslide.The sliding mass composed a deposit dam,400 meters long along river,880 meters along the slope,and with a plain area of 18.2 thousand m^2.And the Guantan barrier lake is formed because of the dam blocking the Jushui River.