Analysis Of Material Source Erosion And Migration Characteristics Of Debris Flows In Strong Earthquake Areas

After the Wenchuan Earthquake,the strong earthquake caused a lot of loose accumulations in the mountains of Miansi Town,Wenchuan County,resulting in a lot of loose accumulations.The local rainy and heavy rainfall washed the accumulations and caused frequent debris flow disasters.According to related research^[1],although the debris flow disaster in this area is less than a few years after a strong earthquake in the next five years,it is still in a strong age and the probability of occurrence is greater than before the earthquake.Therefore,studying the source erosion and accumulation characteristics of loose accumulation sources in the area has very important practical significance for the prevention and warning of debris flow disasters in the area.In this paper,taking the debris flow of Chutou gully as an example on August 20,2019,through the combination of remote sensing images,aerial photographs of unmanned aerial vehicles and on-site survey data,the characteristics of accumulation and erosion of the accumulation source of Chutou gully are analyzed.On this basis,the well-balanced numerical method is used to simulate the movement and accumulation characteristics of debris flow.According to the simulation results,the dynamic process is studied,and basic data and maintenance suggestions are provided for related engineering construction.The main work results are as follows:?1?On-site investigation and study of the engineering geological data in the study area to determine the engineering geological conditions such as topography and stratum lithology,and to divide the formation area?including the main ditch and each branch ditch?,the circulation area and the accumulation area of the Chutou gully and it`s projects geological condition.?2?On-site analysis was conducted on the accumulation source of Chutou gully.According to the analysis,the accumulation source of the Chutou gully can be divided into two types:the collapse and accumulation source and the channel accumulation source.The collapse and accumulation source has a total of 304,000 m³;the channel accumulation source is a total of 1.339million m³,and the role of water flowing in the trench A large number of steep erosion surfaces are formed below.?3?By comparing the remote sensing images before and after the occurrence of debris flow,the macro-change characteristics of the deposits in the Chutou gully are obtained,and the main conclusions are as follows:1)The deposits in most areas of the Chutou gully formation area have no start-up traces and only form There are accumulations in the downstream of the main ditches and small ditches in the district that start to move to the circulation area;2)There are trench deposits directly below the dam body of the second and third-stage blocking dams in the circulation area to start the migration to the downstream;3)The circulation area downstream deposits are gradually widened from upstream to downstream due to the topography of the accumulation area;4)Accumulation in the accumulation area is concentrated in the drainage guide groove,and finally rushed out of the hoe groove,the maximum rushing distance measured 210m,in the trench The siltation area is 8.77×104m².?4?By comparing the field survey data before and after the debris flow and the aerial photographs of the drone,the microscopic characteristics of the erosion and migration of the deposits in the Chutou gully are analyzed,and the following conclusions are mainly obtained:1)The starting position of the debris flow is in the Madicao gully The main ditch near the mouth;2)The accumulation of the upstream of the blocking dam has coarse-fine particle distribution;the erosion degree of the debris flow on the channel downstream of the dam is deepened;3)The downstream channel of the secondary blocking dam is cut by the erosion of the debris flow,there is part of the debris flow solid material accumulates on the bank slope,and eventually forms a steep erosion surface;4)The erosion and accumulation characteristics of the downstream of the tertiary blocking dam in the circulation area have obvious regional changes.B18 slump accumulation is the boundary,and the upstream channel is debris flow.The erosion degree is high;the downstream is eroded by debris flow and is covered by a large amount of debris flow solid material;5)The gully deposits are concentrated in the drainage channel and partly overflowed and submerged part of the dwellings.The maximum distance of the final debris flow was 210m.?5?Determine the parameters used in the well-balanced numerical simulation,and use the well-balanced values to easily obtain the depth and velocity distribution of the debris flow.Based on the simulation results,the following conclusions were obtained:1)The 2%rainfall frequency simulation obtained a maximum rushing distance of 209m and a gully deposit area of 10.1×104m2.The results are most in line with the actual situation;2)Based on previous research results,through simulation results The depth and velocity of the water are analyzed for the characteristics of erosion and accumulation in the Chutou gully watershed.The dynamic characteristics of the provenance in the Chutou gully circulation area are obtained,and the maintenance and maintenance suggestions for the debris flow in the Chutou gully are proposed.