云南鲁甸地震甘家寨滑坡基本特征及失稳机制

Basic Characteristics and Failure Mechanism of the Ganjiazhai Landslide Triggered by the Ludian Earthquake,Yunnan

甘家寨滑坡是云南鲁甸6.5级地震诱发的特大型滑坡,规模达到1×10~7m^3。滑坡堵塞沙坝河,形成堰塞湖,中断交通,造成32户民房掩埋、55人死亡与失踪,是鲁甸地震区规模最大、灾损最严重的滑坡之一。该滑坡是地震诱发陡峻山体上的石灰岩强风化堆积体滑动而形成的特大型岩土质滑坡,表层为10~20 m固结良好的白云质灰岩结构体,中下层为50~60 m具空隙结构的深厚灰岩风化堆积物。滑坡主要的触发因素有:断层滑动方向性效应、地形放大效应、近断层地震动作用、背坡面效应。滑动过程分为坡体震裂松动、后缘拉裂、整体下滑、减速堆积4个阶段,受滑坡体原有地形影响及滑坡动力过程控制,滑坡堆积体形成4级台坎,其中第二级台坎形成高差约2 m的反向堆积。结合野外实际调查数据与滑坡运动力学模型,估算滑体水平滑动至350 m左右处,速度达到最大4.4 m/s,滑动至砂坝河时滑坡前缘速度减至3.6 m/min,堆积于河道,形成堰塞湖。甘家寨滑坡堆积体地形陡峻、堆积物裂缝密集分布,强降雨条件下,容易再次滑动并成灾,建议进行滑坡体的综合治理,控制后缘地表径流、减轻坡体下渗、强化滑坡前缘工程治理,保障交通顺畅,减轻灾害损失。

The Ganjiazhai mega landslide, of which the deposition volume is up to 1 × 10^7 m3, is the most serious landslide disaster triggered by Ludian earthquake （ Ms = 6.5 ） in Yunnan of China. And it dams the river of Shaba, forms a barrier lake, interrupts the traffic, buries 32 houses and kills 55 persons. The investigation indicates that the Ganjiazhai slope consisted of strongly weathered limestone accumulation collapses by intense seismic disturbance and forms a mega rock-soil landslide. The main triggering factors of the landslide include fault dislocation effect, near-fauh ground motion, interface dynamic stress effect and back slope effect. The sliding processes of the landslide could be divided into 4 stages as follows： hill-slope loosening, rear edge cracking, hill-slope overall sliding, slowing down and depositing. Combined with the data of field survey and dynamic model, it is estimated that the velocity of landslide reaches 4. 4 m/s at the distance of 350 m and decelerates to 3.6 m/min near the river bank of Shaba, and finally the landslide accumulates in the river and forms a barrier lake. This landslide could easily reslide under the condition of heavy rainfall, because of the steep terrain of landslide body and the massive loose deposits with dense cracks. The comprehensive mitigating measures, including draining surface runoff of rear edge, reducing infiltration of landslide accumulation and strengthening engineering control of landslide front, are strongly suggested to ensure the traffic moving smoothly and reduce disaster losses.