Research On Freeze-thaw Slope Of Relationship Between Soil Detachment Rate And Erosion Factors Under Runoff Scour

The soil melt in the daylight but freeze at night during the period of thawing in spring, However, the physical and mechanical properties of soil, for example, the soil shearing strength, get changed under the repeating effects of the freeze-thaw process, leading to the soil stability damaged and it’s erosion durability reduced, under this circumstance, with the compound action of water erosion and gravitational erosion, the severe soil and water loss can happen easily. The purpose of this article was to simulate the scouring experiment of thin layer water with two slopes(10°,15°), four thaw depth(2,5,8,11 cm)and two flow rates(3 and 9L/min), has been taken into consideration in this experiment under the circumstances of scouring the slopes at outside, researching the hydrodynamic parameters variation characteristics of the thin layer water flow under the effect of the freeze-thaw process, analyzing both the main influencing factors on the soil detachment rate, and the corresponding relationship between this rate and the hydrodynamic parameters at the same time. The Stepwise Regression Analysis had been utilized to establish the prediction model of soil erosion in the freeze-thaw slope, the main conclusion of this experiment were as follow:(1) Determine the flow regime on freeze-thaw slopeAccording to Reynolds number and Froude number, the flow regime within this trial stretch consisted of laminar flow and supercritical flow. Reynolds number and Froude number could be expressed as a power function of flow and slope under the different original thaw depth, besides, with the increasing of that depth, the influence of flow exerted increasingly higher on the Reynolds number, while the function of slope got lower gradually, furthermore, the slope could be more effective than flow to the Reynolds number when the original thaw depth lower than 5cm, on the contrary, the influence of flow became greater than slope gradually; however, with regard to the Froude number, both the flow and slope exerted increasing higher influence on that number, and the influence of flow was greater than slope. Above all, there showed a significant correlation between Reynolds number and Froude number, and the power function relationship among the two numbers and the runoff depth showed well, so the depth could be utilized to estimate the flow regime in the slope.(2) Obtain the change rule of hydrodynamic parameters on freeze-thaw slopeThe runoff depth and the resistance coefficient could be expressed as a power function of flow and slope, for the slope played the main effect on the runoff depth, meanwhile, the flow exerted the main impact on the resistance coefficient. There was a highly significant correlation between the runoff depth and the resistance coefficient (P<0.01), and the resistance coefficient got decreased as a power function with the increasing of the runoff depth. The flow sheer stress, stream power and unit stream power had a constant increase of power function with the rise of flow and slope, and the stream flow had a stronger influence than slope, but what affected the shear stress and unit stream power most was slope. Then with the original thaw depth becoming deeper, the effect of flow on the flow shear stress and stream power was increasing whereas that of slope was at the down trend, and no stable consistency in the influence on unit stream power had been seen. Reynolds number, Froude number, Runoff depth and resistance coefficient were highly significantly correlating with stream power (P<0.01), which could be the description of stream power variation; meanwhile, there was also a highly significant correlation (P<0.01) between the Froude number and flow shear stress, stream power and unit stream power, making the description on the features of slope flow from the aspect of power or energy.(3) Obtain the change rule of soil detachment rate on freeze-thaw slopeIn this experiment, the soil detachment rate was increasingly serious with the increase of slope and flow. Under the same conditions, the detachment rate was highest at 5cm depth of the original thaw depth when the flow was 3L/min, with a decrease trend of soil corrosion at deepening the original thaw depth; and the rise trend of soil corrosion rate was more and more significant when the slope was raised.(4) Put forward the main influence factors of soil detachment rateResult among the grey relational degree between these factors and the soil detachment rate, flow occupied first place, with slope come second; among the fuzzy nearness degrees between these factors and the soil detachment rate, stream power occupied first place, with both the flow and the original thaw depth being higher than slope; stream power played a crucial role in determining the soil detachment rate, followed by the original thaw depth and the flow sheer stress exerted the most considerable effect indirectly on the soil detachment rate through other factors. Conclusion that come from the analyses of three approaches showed that stream power, flow, the thaw depth and slope were the main factors of influencing the soil detachment rate. The soil detachment rate and flow, slope, original thaw depth was power function relationship; with shear stress, stream power and unit stream power was liner. Finally, a calculating equation of the soil detachment on freeze-thaw slopes. At the basis of original thaw depth and stream power had been presented by means of the step wise regression analysis between the soil detachment rate and seven erosion factors.