Study On Erosion Mechanism Of Soil-rock Mixed Colluvial Soil Slope During Concentrated Flow

Colluvial soil is an important component of Benggang and a typical soil-rock mixture with high content in gravel. However, the research of soil-rock mixed colluvial soil isn’t clear, which become another important study of the colluvial erosion. This study chose soil-rock mixed colluvial soil from Anxi county, Fujian Province as the research object, which is selected to study the feature of sediment yield, sediment particle properties and hydrodynamic mechanism that is affected by four gravel contents(0%,20%,40%,60%), four discharges(2 L·min-1,4 L·min-1,8 L·min-1,16 L·min-1) and four slopes(10°,20°,30°,40°) in indoor artificial runoff experimental condition. The conclusions are as follows:(1) The process of sediment yield indicates that the sediment yield overall increases first, and then decreases, reaches a steady finally with erosion duration in different discharges and 30° slope. Sediment volume increases with increasing discharge and slope, whereas sediment concentration decreases with increasing discharge and increases with increasing slope; sediment volume and sediment concentration firstly decreases and then increases with increasing gravel content at the discharges of 2 L·min-1 and 4 L·min-1, existing critical gravel content (20%-40%), but sediment yield and sediment concentration increases with increasing gravel content at the discharges of 8 L·min-1 and 16 L·min-1. Gravel content, discharge and slope can be used to predict sediment yield rate and sediment concentration of soil-gravel mixed colluvial slope correctly.(2) Coarse sand and fine silt content in sediment particles is higher in different conditions. In the late experiment, distribution of sediment particle size is in accordance with the tested soil, namely with an overall erosion. Sediment particle size distribution, especially the enrichment ratio can be used to characterize intensity of the slope soil erosion. Soil without gravel erodes integrally with erosion duration, when joining the gravel into soil, this rule is broken gradually, when gravel content is 60%, sediment will no longer be carried integrally. Sediment particles MWD increases with increasing gravel content, which indicates that the existence of gravel coarsens sediment particles. Mean weight diameter changes with gravel content, discharge and slope, the migration of the particles with different sizes is selective.(3) With the extension of erosion duration, flow velocity decreases, Reynolds number increases firstly and then decreases, Froude number decreases firstly and then reaches a steady, resistance coefficient increases with volatility in different conditions. In most cases, flow state of tested slope belongs to turbulent flow, flow pattern belongs to rapids. With erosion duration, flow shear and stream power both increases firstly and then decreases, unit stream power shows a trend of decrease. Gravel content, discharge and slope can be used to predict the hydrodynamic parameters (flow velocity, Reynolds number, Froude number, resistance coefficient, flow shear, stream power and unit stream power). Reynolds number, resistance coefficient, flow shear and stream power can be the primary choices to be the hydrodynamic parameters of sediment transportation of soil-rock mixed colluvial soil. With the increase of gravel content, flow shear, erodibility parameters of stream power and unit stream power increases, the critical flow shear and critical unit stream power decreases, the critical stream power has no obvious regularity.