Indoor Simulation Experiments On Rill Erosion Of Landslide Depositon Slope In Wenchuan Earthquake Area

"5.12"wenchuan earthquake in2008caused a large number of landslide events and the landslide deposition developed and distributed mainly along the river and tributary valley. The deposition transported a large number of sediment particles to the downstream water which caused the riverbed elevation, channel sedimentation and be a huge potential safety problems result of concentrated flow under the rainfall. In this study, the indoor experiments on earth-rock mixed steep slope with scouring flow method were conducted, and then the rill hydrodynamics characteristics and the features of runoff and sediment yield under different flow rates, slopes, ratio of earth and rock contents were measured based on the angle of repose, bulk density, ratio of earth(<2mm) and rocks(2-7mm) that measured in the field investigation. The main water erosion factors that affect the soil erosion rate also be discussed. This study preliminary illustrated the soil erosion process of landslide deposition slope and provided theory basis for the establishing soil erosion model of earth and rock mixture slope. The main results were listed as follows:(1) Under each flow rate of34°and4L/min of36°, the average flow velocities under earth were significant higher than that of earth-rocks mixed. Under the8L/min and12L/min of36°, the average flow rates increased gradually and became higher than that of earth. The average flow velocities under all of the groups decreased with the scouring times flies. The ratio of earth-rocks affecting the Reynolds number was complex. The flow regime was almost transition flow and turbulent flow during the experimental time. The influence of ratio of earth and rocks on Froude number had the same rules with that on average flow rates. As time goes on, Froude number transformed from supercritical flow to subcritical flow, especially the changes were obvious under the earth and rocks mixed. Darcy-weisbach friction increased slowly, and then increased rapidly, decreased sharply at last with scouring time flies. The Froude number were0.16-14.40under the earth and0.16-29.68under earth and rocks mixed. Darcy-weisbach friction had negative correlation with Reynolds number.(2) Runoff yield decreased as volatility with the scouring time flying. The rank of different runoff total yield under different earth-rock ratio was as follow:1:3> total earth>1:2>:1. The runoff yield increased with the multiplied flow discharge, but the increased multiplied rates were inconsistent. The sediment yield also had a rank as follow:1:3>1:2>total earth>1:1, the flow discharge had the same effect on sediment yield as the runoff yield, both of the earth-rock ratio and flow discharge had significant effects on sediment yield. The sediment concentration also changed as volatility. The average sediment concentration of1:2was the largest, followed the total earth and1:1, the average sediment concentration of the1:3was smallest. The flow discharge had no significant effect on average sediment concentration.(3) The soil erosion rate, stream power and unit stream power decreased as volatility, while hydraulic shear stress firstly increased and then decreased, unit energy of water-carrying section firstly decreased and then increased lastly decreased with the scouring time delaying. The values of ratio1:3and earth under soil erosion rate and water erosion factor were larger than the ratio1:2and1:1. The flow discharge had significant effects on soil erosion rate and water erosion factor. It concrete manifestation was:soil erosion rate, hydraulic shear stress, stream power, unit energy of water-carrying section increased with the flow discharge multiply increasing, while the unit stream power changed intricately. The relationships between soil erosion rate and water erosion factor were also complex. They were highly significant between the soil erosion rate and water erosion factor under the earth, while they were significant or not under the earth-rock mixed. The hydraulic shear stress had so highly significant positive power relationship with the soil erosion rate that it could be used to predict and evaluate the soil erosion rate on the landslide deposition slope.(4) Manning’s n increased slowly, and then increased rapidly, decreased sharply at last with the scouring times. The n values were following the rules:1:3>1:2>1:1>earth under the four ratios of rock and earth. The n values decreased while the flow discharge increased, but the extension of change was not significant. There was significant positive power relationships between flow depth (h) and n values. The n values had no significant relationship with Reynolds number but had significant negative power relationship with Froude number. The rate of Manning roughness coefficient to flow depth(n/h) had also significant negative power relationship with Reynolds number, while had no significant relationship with Froude number. The rate of Manning roughness coefficient to flow depth (n/h) had extremely signifiacant negative linear relationship with the average flow velocity, shear stress, unit stream power and extremely signifiacant negative power relationship with stream power, unit energy of water-carrying section when a significant negative linear relationship with soil erosion rate.