FORMATION CHARACTERISTICS AND KINEMATICS 3-D SIMULATION OF ROCKFALL EVOLVED FROM SHATTERED MOUNTAIN—CASE STUDY OF SANGUANMIAO VILLAGE ROCKFALL IN WENCHUAN COUNTY

Sanguanmiao shattered mountain is located in Wenchuan earthquake area,where two post-earthquake rockfalls had occurred on July 20,2018 and August 22,2019,respectively. They caused considerable economic losses and threatened the safety of residents. Therefore,this paper performs a detailed analysis on study area by using field investigation of dangerous rocks in shattered mountains,unmanned aerial vehicle survey and three-dimensional numerical simulation,clarifying the mechanisms and kinematic processes of the rockfall evolved from shattered mountain. Meanwhile,the risk of potentially dangerous rock area has been assessed. The results suggest the following findings. The formation process of this type of rockfall could be divided into three stages,including early structure and unloading crack development of potentially dangerous rock slope,formation of shattered mountains(dangerous rock mass) and occurrence of post-earthquake rockfalls. Firstly,the rock masses in the source area formed unloading fissures during the incision of the Minjiang River,and then under the role of the "5.12" strong earthquake and aftershocks,tensile fissures formed and the ridge top deformed and shattered,forming shattered mountains. Eventually,heavy rainfall in the rainy season directly triggered the rockfalls. The three-dimensional simulation software RocPro3D is used to simulate the accumulation range and the dominant moving trajectory,which are compared and verified with the existing accumulation area,comprehensively obtain the rock and soil characteristic parameters,and further simulated and predicted the possibility of the dangerous rock area based on the validated parameters. The movement characteristics,dominant moving trajectory,moving velocity,energy and bounce height are analyzed to obtain the impact extent of the rockfall. The results can provide an insight into potential disasters reduction and prevention of shattered mountain failure in the strong earthquake area.