汶川地震触发平溪村滑坡特征及成因分析

Characteristics and cause analysis of the Pingxi landslide triggered by the Wenchuan earthquake

平溪村滑坡是汶川地震触发的高速岩质滑坡,面积为3.7×104m2,体积约65×104m3。滑坡距离映秀—北川发震断裂带中的石坎断层不足500m,在强大地震力作用下,滑坡滑动面陡峭、粗糙,与重力作用下呈圆弧、平滑的滑面迥异。地震触发的滑坡可分为三个阶段:①震动拉裂阶段;②摩擦阻力降低、"锁固段"剪断阶段;③滑体溃滑,高速流动堆积阶段。然后结合结构面的力学分析,通过数值模拟对地震作用下的应力变化和震裂机制进行了初步分析。

The Pingxi landslide is a highspeed rock landslide located in Pingwu County of Mianyang City. It was triggered by the Wenchuan earthquake. It covers an area of 3.7 x 104 m2 and its volume is 65 x 104 m3 , the sliding direction is about 340° This landslide is mainly composed of Cambrian crystalline limestone, with the development of the following two control structural plane： ①N55° -65°W/NE and ② N75°-85°E/SE. The distance between the landslide and the Shikan fault in Yingxiu - Beichuan seismogenic fault is 500 m or less. Different from the smooth and somewhat arcwall slip surface caused by gravity force, the slip surface of landslide triggered by seismic force is steep and rough. The cause of earthquake-landslide can be divided into three stages： ①the stage of shattering cracking, ② the stage of friction decrease and “ locked section” snipping, and ③ the stage of slope mass sliding- accumulating. Shock cracking occurs within the rockmass, causing the debacle surface to form and interconnect, and constituting the perimeter of slope mass to slide. After the sliding perimeter occurs, “locked section” in the landslide front is snipped sharply, and slope mass slides with high speed along the slip surface. Combining with mechanical analysis of structural plane and using numerical simulation to analyze the stress and earthquake-induced deformation under earthquake are of important significance to the study of earthquake-landslides.