Study On Chain Mechanism Of High-speed And Long-distance Landslide Disaster In Wenchuan Earthquake

The Wenchuan earthquake is a geological disaster with the widest impact,the most casualties,and the greatest disaster relief since the founding of China.The number and scale of secondary geological disasters such as collapses,landslides,mudslides,and dammed lakes caused by earthquakes are extremely huge.In the process of strong earthquakes,especially in the vicinity of the earthquake fault zone,there are often extremely complex dynamic environments.High-speed long-distance landslides induced by strong earthquakes generally have more complex motion processes,and also have some rare dynamic characteristics under non-seismic conditions.Therefore,based on the systematic study of the mechanism of high-speed and long-distance landslide movement,further discussion of the disaster mode and formation conditions of the geological hazard chain formed in the study area can not only promote the development and innovation of the geological hazard chain theory,but also contribute to the construction of the project.Disaster prevention and mitigation provides scientific technical support,which has important theoretical and practical significance.This article takes Wenjiagou landslide-debris flow as a typical case,and combines the subsequent debris flow and dammed lake disasters.By studying the mechanism of the disaster chain,the whole Wenjiagou disaster chain is divided into two stages.analysis.The first stage is the Wenjiagou landslide-clastic flow caused by the earthquake.This paper analyzes the formation mechanism and movement characteristics of the Wenjiagou landslide in the processes of excitation,initiation,acceleration,and stopping.The second stage is the debris flow-dammed lake caused by the accumulation.This paper analyzes the development environment,development characteristics and formation conditions of Wenjiagou debris flow.Finally,after the integration of the two stages,the analysis and formation of the chain mechanism of the entire disaster chain.At the same time,at the end of this article,use PFC3D to simulate the entire Wenjiagou landslide movement process,and combine the simulation results and the corresponding physical model to discuss the development process of the disaster chain.The main knowledge and conclusions obtained in this paper are briefly described as follows:(1)The Wenjiagou landslide-clastic flow event is a high-level,long-distance,ultra-high-speed,medium-deep bedrock slip giant landslide-clastic flow process directly induced by a mega-earthquake.The entire event lasted about 1 min,the thickness of the sliding body was 20-30m,the initial volume was about 2.75×10~7m~3,and finally a deposit with a total volume of 5×10~7m~3 was left in the Wenjiagou valley,with a maximum thickness of nearly 150m.(2)The landslides in the study area are mainly earthquake-associated landslides.After analysis,the occurrence of landslides is related to the water system,elevation,slope and aspect of the study area;the debris flow in the study area is affected by topographical factors and is related to the mountain.There were four main collisions.Each collision not only changed the direction of movement of the landslide body,but also made the degree of fragmentation of the landslide body deepened.The material basis of the debris flow disaster in the study area is the landslide-debris flow.The large volume of loose material brought by it,and the surface runoff formed by short-term heavy rainfall is the main inducing factor of the debris flow;the dammed lake in the study area is caused by the loose material caused by the debris flow to block the Mianyuan river channel.Formed,combined with relevant data,it can be concluded that the occurrence of dammed lakes is often related to the seismic intensity,topographical conditions and lithological conditions of the study area.(3)The whole disaster chain of Wenjiagou is as follows:landslide-debris flow moves at high speed under the action of gravity,and with great energy in the process of downward movement along the way,it continuously sweeps and scrapes the trench bed and channel.The solid loose material of the shallow side slope;landslide-clastic flow leaves a large amount of solid loose material in the main channel of Wenjiagou,and the gully bed is steep.Under the action of heavy rain or running water,the soil at the bottom of the channel After being scoured,the undercut gullies are formed.After reaching a certain limit,some of the soil at the front edges of the slopes of the channels on both sides will be empty,and eventually the gullies will be blocked.Under the action of flowing water,debris flows will be formed;all debris flow washed out will accumulate In the main channel of the Mianyuan River,raising the river bed causes the water level of the Mianyuan River to rise,and debris flows silt up the high buildings and roads on both sides of the Mianyuan River.(4)In the process of numerical simulation,the entire Wenjiagou landslide lasted about 120s,the maximum movement speed of the sliding body reached 136.40m/s,the maximum vertical drop was 1347.48m,and the maximum horizontal movement distance reached 4717.29m.According to the data It can be seen that the Wenjiagou landslide is a typical high-speed rock landslide.These results are not much different from the site and previous data.At the same time,the shape of the disaster chain development process deduced based on the physical model and the data obtained by PFC3D is basically consistent with the on-site situation.