Study On Formation, Evolution And Prevention Of Jinmi Debris Flow In Zhashui County

In recent years,human disturbance to the geological environment in mountain areas has been intensifying,coupled with the effect of extreme weather,resulting in frequent debris flow disasters,which seriously threaten the safety of people and property,and restrict the development of economic construction in mountain areas.Therefore,it is imperative to study the formation mechanism of debris flow,to predict the evolution of debris flow disasters reasonably and to find effective prevention and control measures,and to establish a system of method for the formation,evolution and prevention of debris flow disasters in mountain areas.Taking Jinmi debris flow in Zhashui county as the research object,through field investigation and engineering geological mapping,this paper found out the zoning characteristics and material source characteristics of Jinmi debris flow.Then analysed and calculated the physical and mechanical parameters of the debris flow,such as its gravity,flow rate,flow discharge and impact force.This study analyzed the causes of debris flow from three aspects: topographic,geological and hydrodynamic conditions.The formation mechanism of debris flow is discussed based on ring shear test.The periodic regularity of debris flow outbreak is inferred by modulus ratio coefficient analysis method.The stability and evolution trend of debris flow basin are discussed.The dangerous range and risk value of debris flow are predicted.On this basis,The research suggested the prevention and control measures of Jinmi debris flow.The main progress of the study is as follows:(1)The zoning characteristics of Jinmi debris flow are obvious.When calculating the new solid source reserves of debris flow in the future,the source of slope erosion is predicted according to the erosion modulus,and the dynamic source of lateral erosion channel is considered.By means of comprehensive classification,the types of Jinmi debris flow are summarized as follows: valley debris flow formed under natural conditions,stimulated by rainstorm,modern high frequency hydraulic type,dilute and mixed type.(2)The critical soil water content for the initiation of Jinmi debris flow is 0.354 by Hu Kaiheng's empirical formula,and the critical slope for the initiation of Jinmi debris flow is 13.9 degrees by Fei Junxiang's empirical formula.It is considered that the debris flow occurred in Jia Jia Gou in 2012 is a landslide-type debris flow.The transformation process can be divided into landslide instability stage,transformation stage and debris flow stage.Through the ring shear test,this study found that silty clay with smaller particle size would be aggregated and liquefied in the shear plane due to the delamination and fragmentation of particles in the sliding shear process of the sliding body,which would promote the sliding of the sliding body downstream of the channel and disintegrate into debris flow.(3)According to the characteristics of Jinmi debris flow,we divided its development and evolution in one cycle into three periods: incubation period,development-prosperity period and recession period.It is considered that the debris flow and rainfall have similar quasiperiodicity.The long period of Jinmi debris flow is 17-24 years and the short period is 4-9 years by modulus-ratio product curve method.The vertical profile index of Jia Jia Gou and Zhu Jia Gou is obtained by drawing and fitting.It is considered that the Jia Jia Gou is in the vigorous stage of debris flow,and the Zhu Jia Gou is in the development stage of debris flow.(4)Predicting the dangerous range of debris flow based on Liu Xilin's prediction model,and the comprehensive risk value of the Jinmi debris flow is estimated to be 7.9754 million yuan based on the consideration of economic risk and life risk.On the basis of the above research,this paper suggested that the control scheme of Jinmi debris flow should be "two retaining dams,one check dam,drainage channel,retaining wall and silt removal".Then determined the parameters of each sub-project and carried out the stability checking of the prevention and control project.The results of this study can provide research ideas for the formation mechanism,development and evolution prediction of debris flow hazards in mountain areas.Also provide theoretical basis for debris flow prevention and control.