In October 10th and November 3rd 2018, two landslides happened successively on the right bank of the upper reaches of Jinsha River, which dammed the river at Baige village, Jiangda county, Tibetan Autonomous Region. The dammed lakes and their breaching flood brought about severe disaster to local residents and their production and life facilities along the river. Based on the field investigation immediately after the slides and other related materials, a systematic analysis is made on the formation and process of the slides in the paper. Results show that: 1) the " 10•10" slide is a high position, high shear crack, high speed and incomplete wedge slide and its volume is around 107 m3; 2) geologically the slide is situated in the suture zone of Jinsha River and the bedrock is Xiongfeng gneiss group of Proterozoic, which is characterized by multiphase repeated deformation and metamorphism and is severely mylonitized and altered; 3) the sliding area can be vertically divided into 3 zones of anti-sliding zone, major sliding zone and hauling zone, which are separated roughly at elevation 3 500 m and 3 000 m, respectively. The major sliding zone is of wedge shape cut by two well-developed structural planes, the anti-sliding zone is of tetrahedron shape formed by two undeveloped structural planes, while the hauling zone is completely weathered earth mass mixed with clumped and heavily fractured rock; 4) the slide has two sliding directions of S80°E in the major sliding zone and N70°E in the anti-sliding zone and the elevation of shear crack is around 2 950 m above sea level; 5) the power driving the slide is mainly from the gravity of the wedge in the major sliding zone and the developing process of the slide is the progressive failure of the comparatively intact rock mass in the anti-sliding zone under the gravity of the major sliding zone; 6) the sliding process can be divided into 6 steps. Firstly the major sliding zone and the anti-sliding zone begins, secondly the support-losing hauling zone starts up, thirdly the first started mass collides with the left bank of the river (the bank in Sichuan Province) at high speed, then moves up the slope for around 95 m and laterally to form the debris-scouring zone, fourthly the first started mass moves downward and collides with the mass from the hauling zone above the river and the merged mass punches the river water to form high-speed sandy water jet, resulting in jet-scouring zones on the both banks, fifthly the downslope of the landslide dam fails, resulting in the secondary landslide and finally the punch-induced misty rain leads to the flush of the dam surface; 7) the " 11•3" landslide is the local failure of the earth mass in the hauling zone due to the progressive disintegration of the fractured rock mass acting as retaining wall and its volume is around 3×106 m3; 8) there still exist badly deformed mass in the hauling zone and the estimated volume is 5.5×106 m3, so further sliding and damming risk is big and feasible control measures should be taken. © 2019, Editorial Department of Advanced Engineering Sciences. All right reserved.
