Study On The Particle Size Distribution And Migration Mechanism Of Aggregates During Slope Erosion Of Engineering Accumulation

In the process of soil erosion in engineering accumulations,due to the coupling effect of raindrop splashing and runoff transport,soil aggregates are dispersed and migrated,which in turn affects soil erosion resistance,soil nutrient maintenance,supply and transformation,and seriously affects the stability and vegetation restoration of the accumulations.Therefore,there is a serious lack of research on slope soil aggregates under the combined effects of rainfall and runoff erosion in engineering accumulations,based on field runoff plots(10 m×1 m,slope 36°),through artificial simulated rainfall(rainfall intensity:60,90,120 mm/h)experiments,runoff erosion(discharge flow:10,15,20 L/min)experiments,and combined with indoor soil aggregate particle size analysis,analyze the hydrodynamic characteristics of accumulation slope under different rainfall intensity,discharge flow rate,and their combination conditions,and clarify the distribution and migration characteristics of aggregate particle size during the erosion process of accumulation slope under different erosion driving forces,Revealing the impact of runoff dynamics characteristics under different erosion driving forces on slope erosion and particle size distribution and migration characteristics of aggregates,in order to provide theoretical basis for soil erosion prevention and ecological management of accumulation bodies.The main conclusions obtained are as follows:(1)Under different erosion driving forces,the hydrodynamic characteristics of slope water flow on accumulation bodies vary.Under rainfall conditions,the Reynolds number varies from 38 to 1314,and the slope flow is laminar and transitional;Under the scouring condition,the Reynolds number varies from 79 to2594,and the slope flow includes laminar flow,transitional flow and turbulent flow;Under rainfall and runoff erosion conditions,slope flow includes both laminar flow,transitional flow,and turbulent flow.Compared to rainfall and runoff erosion conditions alone,the flow velocity and runoff power both increase,with a range of increase rates ranging from 92.93%～416.73%and 128.54%～1576.47%;The shear force of runoff increases and decreases,with an increase rate ranging from-28.14%～308.48%;Compared to the individual erosion test,the flow velocity,runoff shear force,and runoff power have increased and decreased,with the increase rate ranging from-8.43%～11.91%,-21.52%～276.11%,and-27.06%～180.36%,respectively.(2)The distribution characteristics of aggregates in the erosion process of accumulation slope under different erosion driving forces are not the same.The mass percentage of aggregates increases with the decrease of particle size distribution,with the largest proportion of aggregates with particle size<0.053 mm;When the particle size of soil aggregates is less than 0.053 mm,the mass percentage of soil aggregates decreases with the increase of drainage flow rate.Under rainfall and runoff erosion conditions,the mass percentage of aggregates shows a fluctuating increase trend with the decrease of particle size distribution,with the largest proportion of aggregates with particle size<0.053 mm;As the discharge flow rate increases,the mass percentage of soil aggregates with particle size>0.25 mm also significantly increases.(3)The migration characteristics of aggregates in the process of slope erosion under the same driving force of erosion are different.Under rainfall conditions,the fractal dimension(D)of soil aggregates decreases with the increase of rainfall intensity;The enrichment rate(ER)of soil aggregates gradually increases with the decrease of particle size,and the enrichment rate(ER)of soil aggregates with particle size<0.053 mm is>1;The average weight diameter(MWD)of soil aggregates increases with the increase of rainfall intensity.Under the condition of runoff erosion,the fractal dimension(D)of soil aggregates decreased significantly with the increase of water discharge;The enrichment rate(ER)of soil aggregates gradually increases with the decrease of particle size,and the enrichment rate(ER)of soil aggregates with particle size<0.053 mm is>1;The average weight diameter(MWD)of soil aggregates first increases and then decreases with the increase of drainage flow rate.Under the condition of rainfall and runoff scouring,when the discharge is 10 and 20 L/min,the fractal dimension(D)of soil aggregates decreases with the increase of rainfall intensity,and when 15 L/min,the fractal dimension(D)of soil aggregates first increases and then decreases with the increase of rainfall intensity;When the discharge flow rate is 10 L/min,the enrichment rate(ER)of soil aggregates gradually increases with the decrease of particle size.At 15 and 20 L/min,the enrichment rate(ER)of soil aggregates shows a trend of first increasing and then decreasing with the decrease of particle size distribution;The average weight diameter of soil aggregates with a rainfall intensity of 60 mm/h first increases and then decreases with the increase of drainage flow,while the average weight diameter of soil aggregates with a rainfall intensity of 90 and 120 mm/h increases with the increase of drainage flow.(4)Different erosion driving forces lead to different erosion mechanisms on the slope surface of accumulation bodies.Under individual rainfall and runoff erosion,runoff power is the best hydrodynamic parameter to describe the erosion of accumulation slope.Under the conditions of rainfall and runoff erosion,flow velocity is the best hydrodynamic parameter to describe the erosion on the slope surface of the accumulation body.Under rainfall and runoff scouring,there is a very significant power function relationship between sediment yield rate and flow velocity(R~2=0.221～0.514,P<0.01),and a very significant power function relationship between sediment yield rate and runoff power(R~2=0.232～0.611,P<0.01).Under rainfall conditions,flow velocity is the most closely related dynamic parameter to the characteristics of soil aggregates.Under the condition of runoff scouring,Reynolds number is the most closely related dynamic parameters to the characteristics of soil aggregates.Under rainfall and runoff erosion conditions,runoff power is the most closely related dynamic parameter to the characteristics of soil aggregates.