Failure Mechanism And Movement Process Inversion Of Zongrong Ancient Landslide On The Se Margin Of Qinghai-tibet Plateau

Large-scale ancient landslide deposits are widely distributed along the JinshaRiver fault zone on the Qinghai-Tibet Plateau’s SE border,particularly in the mountains and valleys of the Three-River Basin,where there have been many river-damming events of large-scale landslides in history.Large-scale and river-damming landslide and its disaster chain seriously threaten the safety of residents’ lives and property.Furthermore,the Three-rivers Basin on the SE edge of the Qinghai-Tibet Plateau is a key area of China’s hydropower planning,which is linked to the achievement of important goals like "Carbon peaking" and "Carbon neutrality",large-scale and riverdamming landslides on both sides of the strait have adverse effects on the major national infrastructure such as hydropower stations in the basin.Therefore,revealing the failure mechanism and river-damming process of the large-scale landslide has important guiding significance for the analysis of disaster scenarios and the future prediction of large-scale landslide disasters in the region.It is also of great value to ensure the safe construction of the project and the people’s living and working in peace and contentment.This thesis studies the Zongrong landslide,a large-scale and river-damming ancient landslide in the Jinsha-River fault zone on the SE margin of the Qinghai-Tibet Plateau.Using the methods of data collection,field investigation,dating,laboratory rock mechanics test,the geological environment and development characteristics of Zongrong landslide were analyzed in detail,and the causes of Zongrong landslide were analyzed from a theoretical point of view.On this basis,the discrete fracture network(DFN)was established by using the fracture data obtained in the field,and the artificial synthetic rock mass technology(SRM)of PFC2 D is adopted.The DFN model was embedded into the slope model to form the SRM model,and then the numerical simulation is carried out to study the failure mechanism and movement process of landslide.The main research contents and conclusions of this thesis are as follows:(1)Based on the engineering geological conditions of the study area,the general situation of the landslide,and the dating,the cause and age of the landslide are analyzed.Field investigation shows that the landslide is developed on an anti-dip slope composed of Paleozoic amphibolite strata.The landslide body is about 1120 m long,900 m wide.After the sliding mass fell,a landslide dam was formed at the valley bottom,blocking the Jinsha-River,forming a barrier lake.The residual accumulation is about 1137 m wide and 210 m high.OSL dating of lacustrine sediments suggests that the landslide occurred at least 5.4 ± 0.3 ka ago.The study area has a dry climate with little precipitation and much higher evaporation than rainfall.As a result,it is speculated that rainfall was not the primary cause of the landslide.The surrounding geological structure background and fault activity history,in addition to the typical characteristics of the sliding source area of seismic landslides,it is considered that Zongrong landslide is likely to be induced by earthquake.(2)Establishment of SRM model based on discrete element.The field investigation shows that the rock mass fractures in the sliding source area are developed.Three groups of important fracture data were collected on the exposed bedrock area next to the highway behind the landslide.After statistical analysis of these data,it is found that the dip and dip-direction of the three groups of fractures obey gaussian distribution,trace length obey lognormal distribution and spacing obey uniform distribution.According to the probability distribution function and function value obeyed by fracture,DFN was generated by using the Fish language.Using the technology of SRM,the DFN model was imported into the slope model to form a SRM slope model.(3)Carry out numerical simulation to study the failure mechanism and movement process.Numerical simulation results show that the sliding process of the landslide lasted for 120 s,and the maximum speed of the landslide block reached 69 m/s,which had obvious high-speed and long-distance characteristics.The failure process of landslide can be divided into 4 stages:(1)t = 0～5 s,the rock mass has cracked and relaxed,the slope has toppled and deformed,tensile cracks have appeared and expanded at the trailing edge,and the locking section at the leading edge has prevented sliding;(2)t = 5～10 s,the trailing edge sliding surface has basically formed and extended to the middle;(3)t = 10～15 s,shear slip began on the top and front rock masses;(4)t = 15～20s,the locking section has been sheared and broken,the sliding surface has been penetrated,and the slope is unstable;t = 20～120 s,the landslide piled up in the river,causing the river-damming.The main reasons for the high-speed movement of the landslide are not only the sudden release of the energy stored in the locking section when it is cut and the inertia of the ground motion,but also the acceleration of the steep slope acceleration belt at the leading edge of the slope.The collision of the rock mass during the sliding process is the primary cause of the landslide’s fragmentation.The entire landslide body exhibits overall motion characteristics,with no signs of stratification.In the process of landslide movement,frictional energy consumption is the primary energy consumption mechanism.Blocking the Jinsha-River is mainly gneiss that slipped off the front edge of the landslide.The accumulation exhibited a‘reverse-grading’ arrangement with large particle size in the upper part and small particle size in the lower part.