Experimental Study On Effects Of Freezing And Thawing On Soil Erosion On Sand Covered Slope In Loess Hilly Region

The ecotone of the geomantic erosion of the Loess Plateau is combined with several kinds of erosion forces such as hydraulic erosion,wind erosion and freezing thawing erosion,and forms a special erosion mode superimposed on several erosion types of "water erosion-wind erosion-freezing thawing",and a variety of erosion forces overlap in time and space,and the soil erosion range is also strong.In this study,using the loess slope as the research object,through the indoor simulated freezing and water discharge scour tests,the characteristics of the runoff and sediment process and the change of water and sediment,the temporal and spatial variation characteristics of the hydrodynamic parameters and the erosion energy parameters,and the response relationship between the erosion dynamic parameters and the runoff sediment were analyzed.The main conclusions are as follows:(1)The characteristics of runoff and sediment yield on different slopes were analyzed.Compared with the control slope,the initial flow time of the sand covered slope was prolonged,while the freezing and thawing effect shortened the initial flow time of the slope,and the total yield of the frozen slope surface and the frozen slope surface was significantly different from the control slope surface(p<0.05).The total sediment yield of the frozen slope surface,the control overlying slope surface and the frozen overland slope surface was the same as that of the control slope surface.Significant difference(p<0.05);the runoff yield strength of different treatment slopes is roughly divided into two changes:"fast rising relative stability" and "relative stability".The effect of freezing and thawing on the yield strength of the bare slope slope is greater;the trend of sediment yield in the bare slope slope is more stable with the time of production flow,and the sand production of the slope surface is strong.The degree of volatility is larger,freezing and thawing and covering effects of sediment strength Shapo face are larger.(2)The temporal and spatial variation characteristics of hydrodynamic parameters on different slopes were analyzed.The average value of Reynolds number at different times is less than 500 at different time.It is a laminar flow.The mean value of Froude number is more than 1,which belongs to the jet stream.After the soil freezing,the flow velocity in different sections is more intense with the time of runoff,and the flow velocity in different sections of the slope shows a more obvious stratification.The soil drag and soil drag coefficient increased at different times and after the soil was covered with sand.(3)The temporal and spatial variation characteristics of soil erosion energy parameters under different treatments were analyzed.The average value of the shear force and the runoff power of water flow at different times and different sections of the slope is lower than that of the slope surface.The shear force of the frozen slope surface and the frozen slope surface will fluctuate more violently with the flow,which indicates that the effect of freezing and thawing on the shear force of the slope is greater,and the freezing thawing effect is greatly increased.The separation ability of runoff erosion on slope soil.The temporal and spatial variation characteristics of runoff power in different treatments are approximately the same as those of runoff.(4)There is a power function relationship between different dynamic parameters of erosion and runoff intensity and sediment yield intensity.The correlation relation between flow intensity and various parameters is resistance coefficient>Manning roughness coefficient>Froude number>flow shear force>runoff power>flow velocity = Unit runoff power>Reynolds number;the order of correlation between sediment yield and parameters is resistance coefficient>Manning roughness series>flow shear force>runoff power>Renault.Number>Froude.Relatively speaking,runoff resistance(drag coefficient and Manning roughness coefficient)is a good parameter to describe the dynamic process of slope erosion under this test condition.