| Debris flow is a solid-liquid two-phase fluid formed by the coupling of loose soil and water,and is a common mountain hazard.After the Wenchuan earthquake,a large area of the mountain in the strong earthquake area was cracked,and tens of thousands of collapses and landslides occurred,and a large number of loose slope accumulations were accumulated on both sides of the mountain bank,which was easy to be damaged under the action of runoff.These loose slope deposits are one of the important ways for the formation of debris flows,and they are also an important source of supply during the development of the debris flow.With the passage of time after the earthquake,these deposits have become more and more important for the supply of debris flow.This article takes the lateral bank accumulation as the research object,through indoor flume experiments,the soil activity process of debris flow gully deposits under the action of runoff was studied,the characteristics of each stage of the destruction process were summarized,and the random law and erosion characteristics of the lateral erosion development process of gully deposits were revealed.Finally,Refer to the physical model experiment,based on the CFD-DEM numerical simulation method,to realize the simulation of the accumulation body's lateral corrosion failure process.The main research results are as follows:(1)Based on the existing disaster history data and the field investigation results of the research area,the geometric parameters of each lateral bank accumulation and the channel cross section are counted,and the relationship between the geometric characteristics of the lateral bank accumulation and the channel cross section shape is analyzed.The analysis of field investigation data and disaster history data shows that the accumulation bodies of debris flow gully banks mostly exist as triangular vertebral bodies.The study proposes three dimensionless parameters to define the geometry of the lateral bank accumulation and the trench.The aspect ratio W/H represents the slope angle of the deposits at the maximum compression section of the trench;the shape factor V1/3/H represents the amount of material that can be transported by the runoff;the maximum channel occupation ratio W*=W/Wc,which indicates the degree of blockage of the channel(W represents the maximum width of the deposit in the channel cross section,H represents the height of the deposit,and V represents the volume of the deposit,Wc represents the channel width).46 different lateral bank accumulation in Zhouqu Sanyanyu,Luojiayu,Ergou,Niuquangou,Taoguangou,Qipangou and Dujiangyan Longchi were used as prototypes,and their dimensionless parameters were counted,The results show that the shape factor V1/3/H and the aspect ratio W/H have a significant positive correlation;the aspect ratio W/His mainly located near the value 1;and the data points are relatively concentrated and distributed in a narrow band Area;the distribution of the maximum channel advancement ratio W*=W/Wc is more discrete.(2)Based on the indoor physical model experiment,the soil failure process of the lateral bank accumulation under the action of runoff was investigated.The characteristics of each stage in the destruction process were summarized.The randomness law of the development process of the side erosion of the lateral bank accumulation was described by the probability function.The results show that the erosion process of deposit on the bank of the channel mainly includes the erosion stage of slope toe and instability stage,and the soil failure in instability stage shows paroxysmal and fluctuation;Soil failure time interval fit Poisson distribution and its magnitude fit Power law distribution.The frequency of soil failure increases with the increase of the slope gradient and discharge;under the small bed slope gradient(3°),the frequency of soil failure increases with the increase of fine particle content;With the increase of bed slope gradient(7°),the frequency of soil failure increases first and then decreases with the increase of fine particle content;when the bed slope gradient is large(11°),the frequency of soil failure decreases with the increase of fine particle content.(3)Through the experimental data,the variation law of the lateral erosion rate of the accumulation body with the influencing factors was analyzed;and considering the three-dimensional characteristics of the accumulation body,the variation law of the erosion rate with time and space was analyzed.The bed slope of 70 is the critical slope of the accumulation body erosion rate.When the slope is less than 7°,the average erosion rate increases with the increase of fine particle content;when the slope is greater than 7°,the average erosion rate decreases with the increase of the fine particle content.The average erosion rate decreases significantly with the increase of density.The average erosion rate increases as the slope of the bed increases.The average erosion rate increases as the upstream flow rate increases.The ranking of the weight of each influencing factor is:density?flow?slope?fine particles.The size of the lateral erosion rate at any point of the accumulation body is consistent with the distribution of bed shear stress at that point.At different time points,the erosion rate first increased and then decreased with the increase of the relative position x/L of the observation section.The point of maximum erosion rate usually appeared at a position slightly to the left of the central axis of the accumulation,and As time changes,it gradually moves downstream.At the same time,with the development of the lateral erosion broadening process,the overall average erosion rate shows a downward trend.The lateral broadening process of the lateral bank accumulation can be summarized as follows:initial state of trench bank deposits?deposit body enters scouring?collapsing body falling sedimentation?collapsing body enters scouring state?collapsing body erosion ends?enters the next scouring cycle process.The total time required for a complete lateral widening process is:(?)(4)Based on the particle discrete element method,the CFD-DEM fluid-solid coupling method was used to simulate the process of the lateral bank accumulation under runoff conditions,and the key parameters of the deposit migration process were monitored.The runoff conditions were simulated by the coarse mesh fluid-structure coupling method built in the program to obtain the lateral erosion failure process of the accumulation body,and compared with the real physical model experiment.The simulation results are consistent with the actual side model erosion failure process and The phenomenon is basically consistent.During the process of lateral erosion and destruction of the accumulation body,the amount of source erosion gradually increases with time,but the incremental value gradually decreases.The change of porosity of different parts of the accumulation body has great differences in the process of lateral erosion,and the change of the porosity of the upper layer of the accumulation body has a hysteresis. |
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