Research On High Frequency Debris Flow Evolution And Engineering Treatment Optimization Of Chutou Gully In Strong Earthquake Area

After the"5.12"Wenchuan earthquake,due to the special geological environment,Wenchuan County in the flood season became a high-incidence area of debris flow.As the typical debris flow channel,the debris flow occurred in 2009,2013,2014 and 2019respectively.Disasters and debris flows have seriously threatened the safety of more than 220 people living in Qiangfeng Village,Miansi Town,on both sides of the ditch,and the normal traffic of Duwen highway.Due to the lack of technology and understanding of the early development characteristics of debris flow,the evolution of debris flow,and the setting of debris flow engineering treatment measures,the early treatment projects of Chutou gully debris flow have been destroyed one after another.Therefore,it is of great significance to carry out research on Chutou gully debris flow.The thesis takes the"8.20"debris flow as the subject of detailed investigation,and investigates the development characteristics of the debris flow,the characteristics of the deposits,and the characteristics of the parameters required for numerical simulation.Through the Massflow software,the hazard of the channel basin is divided according to the hazard zoning standard.With the help of advanced technical means such as remote sensing and drones,the evolution of the source of the river basin was studied,combined with the research on the multi-phase engineering treatment plan of Chutou gully debris flow and the current analysis of the engineering treatment measures,the treatment plan was optimized,and finally the mechanical formula and numerical value were adopted.The simulation verifies the optimized treatment project and affirms the optimized plan for the treatment measures of the Chutou gully debris flow project.The main results achieved are:(1)Analyzing the history of debris flow disasters combined with the frequency division of actual outbreaks in branch ditch,Chutou gully is a high-frequency debris flow.(2)The"8.20"debris flow was triggered by special topographical conditions,abundant loose material sources in the watershed,and heavy rainfall during the flood season.Among them,the total amount of provenance is 1426.1×10~4 m~3(the amount of landslide-type provenance is 430×10~4 m~3,the amount of channel deposits is 860.1×10~4m~3,and the amount of slope erosion is 136×10~4 m~3),which can participate in debris flow activities.Dynamic reserves are 293.43×10~4 m~3(avalanche type 147.64×10~4 m~3,trench accumulation type 135.19×10~4 m~3,slope erosion type 10.6×10~4 m~3);With the help of Massflow,the high-risk zone accounted for 31.8%,the medium-risk zone accounted for 21.7%,and the low-risk zone accounted for 46.5%.The barrier dam played an effective role in the interception of substances and the regulation of the flow rate during the"8.20"debris flow outbreak.The danger of blocking the upstream of the dam.(3)Through the analysis of the evolution of debris flow,the total source of debris flow and the scale of disasters show an increasing trend.The provenance type has a clear tendency to transform from avalanche-slip provenance type and slope-surface provenance type to channel provenance.After the provenance conversion,it is more conducive to the start and supplement of the debris flow in the main ditch;Through the evolution analysis of the source of landslides,it is found that the slope of 25～50°and the east and southeast directions in the basin are beneficial to the development of landslides and landslides;The difference between the DSM data before and after the flood season can indicate the change in the deposition thickness of the provenance before and after the flood season,which provides a method guide for the accurate calculation of the total amount of debris flow in the later period.(4)After ascertaining the development characteristics of the debris flow in Chutou gully,the evolution characteristics of the debris flow,and the current analysis of engineering treatment measures,it was decided that the optimization plan of the debris flow was to increase the height of the new 1#block dam by 5 m.Through the calculation of back-siltation formula and mechanical formula,the blocking volume and dam stability after the height of the blocking dam were checked and calculated.With the help of Massflow simulation software,the same parameter characteristics as the"8.20"debris flow(debris flow gravity,design flow,movement time)were compared and analyzed.And friction model)conditions of debris flow flow patterns and hazard divisions,thereby confirming the optimization of debris flow control projects.