Study On Scour Characteristics And Numerical Simulation Of Fully Weathered Granite Trench Backfill Slope In Longling Area Under Rainfall Condition

The entire weathered granite slope in the Longling area was directly backfilled or locally backfilled to form backfill soil after the excavation of the pipe trench for pipeline laying,which destroyed the structure of the soil and its diverse physical and mechanical properties.Under the rainy climate conditions in the Longling area,slope erosion is easily formed.This article quantitatively analyzes the changes in the initial and five-year backfill slope surface flow velocity,slope erosion status,runoff and sediment yields,and particle spatial position change curve under different slope angles and rainfall intensities through field investigations,indoor artificial rainfall simulation experiments,and pfc3 d numerical simulation.And reached the following conclusions..(1)On the whole,the effect trend of rainfall and slope on the flow velocity of soil side slopes in two different states is the same.First,when slope is constant,overland flow velocity under different rainfall intensities is positively correlated with rainfall intensity under the same slope condition.As a whole,the increase rate of velocity increases faster with the increase of slope.Second,when rainfall intensity is constant,overland flow velocity under different slopes is positively correlated with slope variation trend under the same rainfall condition.As a whole,the increase rate of flow velocity increases faster with the increase of rainfall intensity.In addition,the initial and final velocity of soil on the backfilled side slope are both greater than the initial velocity of soil on the backfilled side slope in five years under the condition of the same slope and rainfall.(2)On the whole,the yield of each slope of the initial backfill soil increases rapidly within 7 ～ 10 min of yield,then slows down and eventually becomes stable with the extension of yield duration.The yield of each slope of the five-year backfill soil increases rapidly within 5 ～ 8min of yield duration,then slows down and eventually becomes stable with the extension of yield duration.The overall performance of the initial backfill and the five-year backfill is that the duration of runoff production is extended,and the yield of runoff production is increasing,and the yield of runoff also increases with the increase of rainfall intensity when the slope is constant.In addition,under the same slope and rainfall intensity,the runoff yield of the five-year backfill soil slope is higher than that of the initial backfill soil slope.(3)As a whole.When the slope is constant,the sediment yield of the backfill slope shows the same trend with the increase of rainfall intensity.Under the condition of constant rainfall intensity,the sediment yield increases with the increase of slope.The sediment yield of five-year backfill slope with the same slope and rainfall intensity is greater than that of the initial backfill.In addition,the fitting function of the difference of sediment yield between the initial backfill and the five-year backfill at different slopes is an exponential function,and the R2 is greater than 0.9.The results show that the difference of sediment yield increases faster with the increase of slope.The fitting function of the difference of sediment yield between the initial backfill and the five-year backfill under different rainfall intensities is an exponential function,and the R2 is greater than 0.68.It indicates that the difference of sediment yield increases faster with the increase of rainfall intensity.(4)Relative to the undisturbed soil,the porosity of the fully-weathered granite backfill in five years increased to 1.13 times,the soil permeability increased by one order of magnitude,the cohesion decreased to 67.6% of the undisturbed soil at saturation,the internal friction Angle decreased to 87.5% of the undisturbed soil,the physical and mechanical parameters were worse,and the slope erosion was more likely to occur.(5)The numerical simulation shows that the evolution process of slope erosion of 30°backfill for five years of fully weathered granite is sheet erosion → rill erosion → trench erosion.The numerical simulation of particle flow reflects the three-dimensional motion trajectories of particles and the distribution of slope erosion degree and water erosion capacity in the slope from the microscopic perspective.