Water Erosion Processes Of Sandy Soil And Sediment Sorting Associated With Transport Mechanism On Slope Of Engineering Accumulation

Engineering accumulation,as a special geomorphic unit spoil shape,the surface material,loose soil structure,lack of plant roots and lack of organic matter,is the main source of soil loss in new production and construction area.Scientifically understanding of the characteristics of erosion and sediment particles and its sorting mechanism on the slope of the construction of production accumulation,which is a major scientific problem to urgently solve the problems of effectively improving engineering accumulation body protection,improving landscape functions and regional ecological safety.In this study,the typical soil engineering accumulation body in the sand area of the northern Loess Plateau is the main research object,with the accumulation of Lou soil in Guanzhong Plain as a contrast.combining process monitoring of traditional slope erosion method with laser particle size analysis,the erosion separation properties of sediment particles as the premise,demarcation of particle size of suspended sediment particles,leaping and contact mass,researching the influence of slope,soil quality,runoff and other factors to soil erosion sediment accumulation body process and particle composition variation on engineering,clarifying the separation and migration characteristics of sediment particles of overland flow and rill flow of water to establish the sediment transport capacity quantitative description,developing the comprehensive sorting index based on composite erosion sediment statistical parameters,and the characteristics of the sediment particles separation and migration in the runoff of the two underlying surfaces are clarified.The main conclusions are as follows:(1)The flow rate of the slope surface of the two underlying surface engineering accumulation body increases with the time,and the slope and the discharge flow rate have a significant influence on the changing process of the yield;The average initial flow time of the sand soil is lagged about 36 s,and the abrupt increase in the early stage of the Sand soil flow rate is obviously larger than that of the Lou soil accumulation body;The sand production rate of sandy soil and soil accumulation is "multi peak and multi Valley" trend with the continuity of water release.The sand yield rate of slope surface increases gradually with the increase of discharge flow rate,and the sand yield amplitude increases with the increase of slope,and the fluctuation is more intense.The sand soil slope surface is more volatile in the first half of the eroded sand yield than that in the first half of the soil erosion rate,and its overall sediment yield is obviously greater than that of the Lou soil under the corresponding discharge flow conditions.(2)There is a linear relationship between the cumulative runoff yield and the scouring time of the two kinds of accumulations.The cumulative runoff yield growth rate of the sand soil slope is larger than that of the Lou soil under large slope and large flow rate.The cumulative sediment yield of the slope surface of the two kinds of engineering accumulations is two function relation with the scouring time,and the cumulative sediment yield is the maximum.The trend of increase is large,while the maximum value of the accumulated sand yield and the corresponding runoff generation time are complicated with the changing rule of discharge volume and slope.With the development of runoff,the runoff and sediment production processes on the slopes of the accumulation bodies are more complex,and are affected by the slope,underlying surface and discharge intensity.(3)Under the different discharge flow rate and slope,the silt particles of the two kinds of accumulations slope are dominant,but the proportion of clay and sand particles is different.Compared sandy soil,the volume fraction of sand particles of Lou soil is reduced by 68.57%,and the proportion of clay particles and particles is higher.The fractal dimension of eroded sediment particles increases with the increase of slope and discharge volume under two kinds of underlying surfaces,and the fractal dimension of aeolian sandy soil is significantly smaller than that of soil slope.At the same time,the relationship between the fractal dimension of sediment particle volume and the content of clay particles,particles and sand particles can be fitted well with the linear model(P<0.01).The fractal dimension has a very significant positive correlation with the clay particles and the particle volume fraction,but it is between the volume fraction of sand particles.A very significant negative correlation was found.The fractal dimension of erosion and sediment particles was mainly determined by the volume fraction of clay particles,followed by sand,and silt particles.Fractal dimension can be used as an evaluation index for the difference of particle size distribution of sediment on different slope surfaces.(4)Under the different slope and flow rate,the concentration of clay particles in the sediment particles under the two underlying surfaces is more than 1(enrichment),and the sand particles are less than 1(deposition),but the silt particles are in the opposite difference,and the small particles are eroded and washed under the two underlying surfaces,and the large particles have a strong ability to resist erosion.The concentration of clay particles increased significantly and then decreased with the increase of the discharge flow rate,and the concentration of silt particles changed little,while the concentration of sand grains decreased with the flow rate,and then decreased significantly with the viscosity of the clay particles(P<0.05);Under each slope and flow,the enrichment rate of clay particles and silt particles is obviously larger than that of the sandy soil,and the concentration rate of sand particles is obviously smaller,and the small particles of the sediment are more vulnerable to erosion and enrichment.The E/U values of the clay particles in the erosion sediment particles both are less than 1,and the particles are about 1,and the sand grains are more than 1 on the whole.The clay particles and sand particles are easily transported in the form of pellets,while the sand grains are mainly carried in the form of single grain.Under the different discharge flow rate,the particle size of 0.05 mm~0.25 mm of sandy soil is the highest,while the particle size of 0.002 mm~0.02 mm is the highest in the Lou soil erosion sediment particles,and the fluctuation of the percentage content of the sand particles in the aeolian soil is smaller than that of the soil.The content of the pellets in the sand soil is lower and the sand soil is less agglomerate than that of the sandy soil,and it is more easily eroded in the form of single particle.(5)Under each discharge flows,the variation trend of <0.057 mm particle size of sandy soil is basically the same in all three periods,and all fluctuates at 10%~15%.When the discharge flow rate is less than 12 L/min,the erosion sediment particles show the distribution of double peaks,when more than 16 L/min,the erosion sediment particles show a single peak distribution,and the LST of the sediment is between 0.057 mm and 0.072 mm,and the sediment particles greater than 55% are carried in the way of suspension / jump.Meanwhile,under the large flow(16,20 L/min),the relative contribution rate of the suspended / jump transport increases with the discharge period;For accumulation of Lou soil,the variation trend of the particle size of <0.023 mm in the three period is basically the same,which are more than 10%,and the >0.023 mm particles are less than 10%.When the discharge flow rate is less than 16 L/min,the erosion sediment particles show the distribution of Shuangfeng,equal to 20 L/min,the erosion sediment particles show a single peak distribution,and the LST increases slightly with the diachronic time,and the eroded sediment particles greater than 65% are carried in the way of suspension / jump.When the discharge flow is less than 16 L/min,the relative contribution rate of the suspension / jump is reduced to the discharge flow rate,and when the discharge is released.When the flow rate is more than 16 L/min,the relative contribution rate of the suspension / jump is increased with the discharge flow rate.(6)Comparing and analyzing the transport mechanism of sand and sediment particles in the two kinds of soil,the content of the particles in the sandy soil is relatively small,and the percentage content of the particles is generally in the 5%~18% fluctuation,while the percentage content of the lou soil particles is roughly 3%~24%,and the <0.031 mm content of the small and medium particles of the lou soil sediment particles is obviously larger than that of the sand soil,while the large particle content is obviously smaller.At the same time,the sand soil is larger than that of the LST Lou soil.The upper limit of the Lou soil particle size carried by the suspended / jump mode in the soil erosion sediment particles is slightly increasing with the release time.Meanwhile,the relative contribution rate of the sediment particles in the sandy soil is lower than that in the suspended sediment particles,and the relative contribution rate is higher in the rolling method.The higher the content of the clay particles in the soil,the stronger the separation of the sediment particles,and the coarse-grained particles in the soil(including the single grain and the single grain).The higher the content of clay particles in the tested soil,the stronger the separation of the sediment particles,and the higher the content of the coarse particles in the soil,including the single grain and the aggregate,the greater the relative contribution rate of the rolling handling mechanism in the erosion process.