Rill Evolution Process And Erosion Sediment Yield In Slope Of Loess Engineering Accumulation

Over the past 20 years, infrastructure construction like water and transport projects have been rapidly developed in China, which produced a large amount of engineering accumulation formed by tons of deposits, creating more soil and water loss. Because of different construction modes, the underlying surface condition of engineering accumulation is complex. Broken topsoil structure, loose soil property, lack of plant roots and low soil anti-scourability can easily cause soil and water loss. In order to analysis the process of rill erosion and explore the changing characteristics of runoff and sediment yield on slopes of engineering accumulation, the article used water-scouring experiment to simulate runoff scouring process under different rainfall intensities in different gradients and slope length, get the following main research conclusion:(1)Rill runoff yield rate shows fluctuation trends over the time continuing in the slope of engineering accumulation, sediment yield rate shows multimodal multi valley trends over the time continuing, rill sediment yield rate is significantly influenced by rill wall collapse, with the increase of the slope length, sediment yield rate fluctuation frequency becoming smaller and magnitude becoming larger. The cumulative runoff and scouring time have a linear relationship, the cumulative sediment and scouring time have the quadratic function relationship, which means that cumulative sediment have a maximum value, cumulative sediment yield increased with the slope length increasing.(2)Rill sediment concentration shows the gradually reducing trends over the time continuing in the slope of engineering accumulation, the slope and flow have faintness influences to sediment concentration, sediment concentration increased with the slope length, the slope, slope length and flow have significant influence to the slope runoff and sediment process, the flow have the majority effect to the slope runoff and sediment process compared with the slope and slope length, the flow have the positive affections with slope runoff and sediment process, the slope and slope length have the negative affections with slope runoff and sediment process.(3)With the scouring time continuing the rill width and depth both shows increasing trend, the rill width and depth both raided development with the first 9 min, the rill width and depth both steady development with the next 36 min, rill width and depth have a logarithmic function with discharge time, rill width and depth both have a positive correlation with flow, the rill width and depth enlarged with the flow increasing, but slope and slope length have a negative affection with the development of rill width and depth.(4)Wide depth ratio rapid decreased in the 0 ~ 27 min, rill erosion rate cut more slowly, after the 27 min wide depth ratio keep it steady, the wide depth ratio final stabilization with 0.81~1.48 under the 10 m slope length, the wide depth ratio final stabilization with 0.88~2.05 under the 15 m slope length, the rill sectional area shows a rectangular shape. With the slope length increases, the width depth ratio increased. Rill cross-sectional area continuing increased with the discharge time, there is a good linear correlation between cross-sectional area and discharge time.(5)The rill development shows slower under the 10 m slope length condition, rill development in a short time of 15 min reaching a stable form under the 15 m slope length condition, Reynolds number gradually increased with discharge time, runoff have the significant effect with the Reynolds number, Froude number decreased with 0~15 min that shows the flow was the rapids state, Froude number maintain steady at the time of 15~45 min that shows the flow was the flow state. Darcy-weisbach between 0.01~0.69 under the 10 m slope length, Darcy-weisbach between 0.01~1.08 under the 15 m slope length, The velocity of flow, Reynolds number, Froude number and resistance coefficient all have the good power function with the discharge time. Water runoff shear stress and power in runoff time is divided into two stages changing, there were increased in the runoff started 20 min and fluctuations changing with runoff after 20 min.(6)Rill morphological indexes ditch rill width and depth have well functional relationship with runoff yield rate, sediment yield rate, cumulative runoff and cumulative sediment.Rill sediment concentration have the significant effect with sediment yield, slope erosion increased with the sediment concentration bigger.(7)Rill erosion runoff yield rate and sediment yield rate have well functional relationship with velocity of flow, Reynolds number and resistance coefficient with engineering accumulation slope, the rill erodibility of engineering accumulation was calculated to be 1.6×10-3 s/m,the critical flow shear stress for rill erosion occurring was 0.38 Pa.