Study On Disaster Mechanism And Risk Assessment Of Debris Flow At The Eastern Foot Of Helan Mountain

Dozens of debris flow gullies are spread in the eastern foothills of Helan Mountain,under the influence of regional climate,it is very easy to form short-duration heavy rainfall in JulyAugust every year,resulting in frequent debris flow disasters,which seriously threatens the safety of public infrastructure and industrial development in the area.This paper relies on the project of Ningxia Natural Science Foundation(2020AAC03222),by means of data collection,image analysis,site reconnaissance and other technical means,the spatial and temporal rules of debris flow development in the area are identified,and the provenance distribution and erosion characteristics are explored with Suyukou Valley as the focus.The dynamic weight system was established by the analytic hierarchy process(AHP)and the dynamic risk assessment of debris flow was realized by the fuzzy comprehensive evaluation method.The indoor and outdoor test equipment independently developed was used to test the physical and mechanical parameters of soil and design the orthogonal experiment with three factors and three levels of soil moisture content,coarse particle content and gully slope,the start of source scouring was simulated and monitoring indexes such as gully form,accumulation form,material scale and gully formation time were determined.The main innovative conclusions are as follows:(1)Debris flow gullies in the eastern foot area are mainly distributed in the middle and northern parts of Helan Mountain,it outbreaks in the area are induced by precipitation and mainly formed in July and August in the past years,confined to the composition of the source soil,the debris flow in the area is sparse debris flow.In the research area,the traffic routes,ancient cultural heritages,water conservancy facilities and agricultural and animal husbandry industrial areas along the eastern foot are the main disaster bearing bodies of debris flow.(2)The dynamic evaluation method was used to evaluate the debris flow in Suyukou valley,the risk of debris flow under five precipitation conditions of light rain,moderate rain,heavy rain,rainstorm and heavy rain were as follows: extremely low risk,low risk,moderate risk,high risk and high risk;Combined with the evaluation results of graded assignment method and the actual situation of the study area,the analysis shows that the dynamic evaluation results are reliable and more reasonable.(3)The source soil of debris flow in the study area is gravel soil,its permeability is strong,which is conducive to the rapid infiltration of surface runoff and easy saturation of soil;According to the model test,when the content of coarse particles in the provenance soil is low(60%),the development model of debris flow is channel-erosion type,and when the content of coarse particles is higher than 70%,the start-up model of debris flow is more consistent with plugging type of debris flow;The scale of effluent was negatively correlated with coarse particle content,and positively correlated with soil water content and gully bed slope,the order of significance of the three factors was as follows: coarse particle content >gully bed slope >soil water content,the most dangerous combination of factor level was: coarse particle content60%,gully bed slope 15°,soil water content is saturated;The significant of three factors for the valleys formation time was not high,and the influence of soil water content was the least,the formation time of the gully was positively correlated with the content of coarse particles and negatively correlated with the slope of the gully bed.