| Choosing the developing typical collapsing in Tongcheng as the research object,Collecting the A layer,B layer,BC layer and C layer developed in the collapsed granite hills.Analyze the condition of runoff and sediment and the discipline of particle size of the different soil layers in Granite Collapse Region through the simulated rainfall experiments.Study on runoff and sediment characteristics,erosion resistance and hydrodynamic erosion characteristics of collapsed soil in granite area.Then the runoff and sediment mechanism,erodibility difference,influencing factors of impact resistance and hydraulic erosion law of soil erosion at granite area were revealed.The study has important significance in theory and practice to reveal the mechanism of runoff and sediment and the research about erosion law of the different soil layers.in Granite Collapse Region.By estimating its soil erodibility K value of different soil layer and the spatial variation characteristics of the erodibility K,Targeting research the formation mechanism of Dilapidated Granite has certain guiding significance.Quantitative study of the soil detachment process of different soil layers in Granite Collapse Region is of great theoretical and practical significance for predicting the soil detachment process accurately and building the physical model of collapsed mound erosion.It also has great significance to enrich the mechanism of collapsing gully erosion,All of those can provide technological support for the monitoring and planning of water and soil conservation of Weathered Earth in Granite Region in the southern red-soil area.The results showed that:(1)The difference between the infiltration rate and accumulative infiltration of the different soil layers was significant with the whole rainfall period.with the extension that rainfall duration,the infiltration rate of the different soil layers descend,and keep stable at the end,and the accumulative infiltration have relatively large difference;The infiltration rate of illuvial horizon is the highest of 0.27 mm/min,was 1.13 times of eluvial horizon,1.76 times of parent material horizon;Horton model can describe the infiltration rate of the different soil layers well(R~2>0.922),and the fitting results confirmed the variation process of infiltration rate of the different soil layers under the simulated rainfall conditions.(2)The difference between the Sediment yield rate and cumulative sediment of the different soil layers was significant with the whole rainfall period.with extension that rainfall duration.The Sediment yield rate of parent material horizon is the highest of40.43 g/L·min,was 1.79 times of illuvial horizon,3.11 times of eluvial horizon;The cumulative sediment of eluvial horizon increased rapidly,illuvial horizon relatively slow growth,The cumulative sediment of parent material horizon increasing in the whole rainfall period and it is greater than that of eluvial horizon and illuvial horizon.the highest loss of the different soil layers is<0.2mm particle size,0.2~1mm particle size second,1~2 mm and>2 mm particle size minimum.With the extension that rainfall duration,The loss of all particle sizes of eluvial horizon are decreased gradually,the illuvial horizonof is gradually increased,the parent material horizon is gradually stabilized.(3)The rate of soil detachment increased with the increase of discharge under the condition of a certain slope and there were significant differences in the rate of soil detachment at different soil layers,the rate of soil detachment of the detritns layer is the highest,the sandy layer second,And the top soil layer is minimum,under the same discharge,the rate of soil detachment of different soil layers were decreased with the prolonging of scouring time decreased firstly and then get stable;the rate of soil detachment of collapse wall at different soil layers is affected by the slope and the discharge and can be fitted by two element power function equation(R~2>0.878)in the experimental condition.mostly,The influence of the slope to the rate of soil detachment of the top soil layer,the red soil layer,The sandy soil layer,the detritns layer is greater than the discharge,And the influence of discharge to the rate of soil detachment of the detritns layer is more than the slope?(4)The different layers of soil erosion of granite weathered soil were significantly different,The average K value of the parent material layer of Granite weathering is maximum,it is 1.20 times larger than the eluvial horizon and 1.03 times larger than the illuvial horizon;And the Stable sediment rate and different grain size loss of different soil layers significantly,Nuo mo method possess the highest sensitivity in estimating the Soil erodibility K value of different horizon it is 1.5 times larger than modified-nomo and 6 times larger than EPIC model method.Therefore,Yusgiantoro method can accurately evaluate soil erodibility value in the south of granite weathered soil.(5)there are significant differences of the soil anti-scourablity in Different Soil Layers,And it decreases with the increase of flow and slope,The range of the soil anti-scourablity is 2.603~12.705 S/g of top soil layer,The range of the soil anti-scourablity is 0.279~5.099 S/g of red soil layer,The range of the soil anti-scourablity is 0.125~0.823 S/g of sand soil layer,The range of the soil anti-scourablity is0.018~0.110 S/g of detritus layer,Under the same slope and flow condition,The top soil layer has the highest soil anti-scourablity,followed by red soil,The detritus layer has the lowest soil anti-scourablity.,the complex effect of slope degree and flow rate on the soil anti-scourablity in all soil layers could be well fitted with the two-variable power function equation(R~2>0.89).There are impact on soil anti-scourablity by the physicochemical properties,mineral composition and mechanical properties of the collapsing gully.Among them,There was a significant positive correlation between soil bulk density,organic matter content,cohesion and shear strength with soil anti-scourablity,0.2~0.02 mm particle content were significantly negatively correlated with soil anti-scourablity,and the correlation was high.Therefore,the soil bulk density,organic matter content,0.2~0.02 mm particle content,cohesion and shear strength can be used as the evaluation index of soil anti-scourablity of collapsing gully.(6)The effects of shear stress and stream power on the rate of soil detachment of different soil layers can be described well by a linear equation(R~2>0.926),The correlation is higher than the polynomial equation(R~2<0.830)which is fitted by the unit stream power.The shear stress and stream power can be well described as hydraulic parameters of different soil layers in Granite Collapse Region.The critical shear stress of the top soil layer,the red soil layer,The sandy soil layer,the detritns layer were progressively decreased,were:0.28Pa,0.13Pa,0.10Pa,0.07Pa,respectively,The erodibility parameter of different soil layers significantly differentiated,the detritns layer is the highest,the sandy layer second,And the top soil layer is minimum.Therefore,On the vertical structure of the collapsed,with the increase of soil depth,The ability of resisting runoff erosion is weakened gradually. |
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