The Laboratory Simulation Research Of Rill Erosion Based On The Orthogonal Design

Rill erosion is one of the main style of slope soil erosion, if there are rill erosion phenomenon on the slope, erosion amount will increase doubled or even dozens of times, therefore, the rill erosion research has always been the important content in the soil erosion research. At present, the domestic and foreign scholars have get a large number of results by research the sediment yield process and mechanism of rill erosion and the influence factors of erosion, and most of these results are based on qualitative analysis of experiment. Because different scholars use different experimental methods and different hydraulic parameters so the experiment results always differently. In this paper, the experiment was designed using the orthogonal experiment and the similarity theory, which established the experiment scale model of the gravelly soil scour trough. By analyzing the influence factor of rill erosion, research on flow mechanical characteristics variation on the all process of sheet erosion-rill erosion and the rill erosion evolution, A rill erosion model was established and some conclusions was draw.The main research conclusions are as follows:(1) Overland flow rate is one of the very important hydraulics parameters, flow and slope are particularly significant affecting factors of the average velocity. With the increase of flow and slope, the average velocity is gradually increased, but the contribution of the flow to the flow velocity is greater than the contribution of the slope to the flow velocity.(2) There is a close relationship between soil erosion amount and the falling cave development. Based on the regression analysis, we found that the average depth of falling cave product can better reflect the law of soil erosion.Time is the main influence factors of soil erosion amount, followed by flow rate, again is slope gradient, and the slope shape is last one. Scouring time and flow rate are particularly significant influence factors of slope surface erosion, As time, flow rate, and slope gradient increase, the soil erosion amount becomes larger, and undulating slope makes for soil erosion.(3) The slope rill flow falls under the category of the rapid flow. The variation range of the Froude number between 0.95 to 1.57, and the variation range of the Reynolds number between 900 to 6500.When the slope flow velocity is small and is more close to the category of laminar flow, but with the increase of flow velocity, Reynolds number increases rapidly, and the slope flow fast into turbulent flow. The flow rate and slope gradient are two important factors that influence the Froude number and Reynolds number. However, the effect of flow rate on the Froude number and Reynolds number is greater than that of the slope.(4) Rill evolution process is actually a process of the development of slope falling cave. Flow, gradient of slope form, time, and the shape of the slope all affect the development of slope falling cave, but the main factors are scouring time and slope shape, the longer scouring time is, the greater the slope fluctuation is, the greater flow rate is, the more favorable for the formation of slope falling cave, and the greater the slope gradient is, the more conducive to the formation of the falling cave. The greater slope fluctuation degree is, the wider the falling cave in the range of slope development is, but the falling cave depth still develop in the central slope.According to falling cave development characteristic, the rill erosion is divided into sheet erosion, rill prototype stage, rill development stage and the rill adjustment stage.In rill evolution process, sheet erosion stage and rill prototype stage is relatively short, and the rill development occupies an important position in rill evolution process, it is the longest.(5) By the building of a rill erosion model, concluding that the critical condition of rill erosion is the depth of slope water. Then the depth of rill water will increase with increasing of flow and slope of groove wall, but decrease when slope gradient increased, and velocity of flow will increase with increasing of flow and slope. The diameter of soil grain which runoff flow can carried will increase with increasing of slope of slope surface and groove wall and flow of rill, but decrease rapidly with increasing of the internal friction angle.(6) We draw conclusions that slope erosion ability improves with increasing of slope gradient when it is greater than zero. And if it is less than zero, that anti-erosion ability improves firstly, and decreases afterwards. There is a critical slope gradient from 7°to 24°, influenced by internal friction angle significantly, increasing with increasing of internal friction angle.(7) Concluding the start velocity formula of rill erosion in surface of slope, the formula shows that the start velocity with the diameter of soil grain on surface are closely related, the larger the grain, the greater the start velocity.