Influence Of Soil Particle Composition On Debris Flow Activity

After the 2008 Wenchuan earthquake,the scale and frequency of geological disasters in Wenchuan earthquake area have greatly increased,which has brought great harm to people’s lives.Through field investigation and data collation,it was found that the topography,landform and climatic conditions of the three basins in the study area did not change much,but the frequency,scale and hazard of debris flow outbreaks after the earthquake were different,and the biggest change of debris flow gully after the earthquake was the increase of material sources.Therefore,the most direct impact of earthquakes on debris flow is manifested in provenance.In the past,characteristic particle size was always used to describe the composition of source,but it has many restrictive factors and human experience.In this paper,based on the scale distribution theory of Li Yong,the effect of soil particle composition on debris flow activity was studied by sampling,particle size test,permeability test and triaxial test data of three debris flow gullies in the study area.The following conclusions are drawn:(1)Under the same climatic and topographic conditions,the scale and frequency of debris flow outbreaks in the three debris flow gullies selected in this paper are quite different.It is found that the strata and lithology of the three debris flow gullies are different,the degree of seismic damage to soil lithology is different,and the amount of deposits in each basin is different,so the frequency and scale of debris flow outbreaks in the three basins are different under the action of precipitation.The outbreak of debris flow in Niuquan gully was more than that in Dry gully,and the outbreak of debris flow in Bayi gully was the least.(2)The particle size parameters are obtained by particle size test,and the scale parameters of debris flow gully soil are calculated by MATLAB.Through the analysis of scaling parameters,it is concluded that the content of fine grains is less and that of coarse grains is more in Niuquangou soil.The content of coarse and fine grains in Dry gully soil is between Niuquan gully and Bayi gully.The content of fine grains in the source soil of Bayi gully is relatively more and that of coarse grains is relatively less,which indicates that the composition of soil grains in three debris flow gullies is different.(3)Through permeability test and analysis of triaxial test data,it is concluded that Niuquan gully has the greatest permeability,because the more coarse grains,the larger the voids between the soil,the easier the fine grains are washed away by water,and the more permeability the soil is;the permeability of Dry gully is next,the permeability of Bayi gullyis the smallest,because with the increase of fine grains,the soil connection becomes closer and closer.The cohesion increases and the permeability decreases.(4)The content and distribution of coarse and fine particles can affect the properties of soil.Under the same other conditions,the soil with more fine grains and less coarse grains has higher strength(such as gravel soil with more clay content in natural state,which has strong cohesion)and is not easy to cause large-scale soil damage;the soil with less fine grains and more coarse grains has smaller strength and is prone to damage.