Study On The Scour Mechanism Of Wide-Graded Earth-Rock Materials Under The Condition Of Overflowing Dam

Aiming at the wide gradation characteristics of the particulate matter in the barrier dam body and the strong non-constancy of the overflowing water flow of the barrier dam,an experimental study on the transport characteristics of the earth-rock material during the failure of the barrier dam was carried out.According to the particle gradation of Tangjiashan barrier dam body,the five groups of heterogeneous soil and rock material particle gradations used in the scour experiment were determined,and the test flow process was determined according to the discharge flow process curve of Tangjiashan barrier dam and the water supply range of the laboratory water supply system.Based on the flume test,the scouring of soil and rock materials under different flow processes,dam body soil and rock material grading,and downstream outflow conditions are carried out.The scouring characteristics,scouring rate,and gradation changes of soil and rock materials after the test are measured and analyzed under different conditions.The main research results are as follows:(1)The impact of gradation on the erosion and transportation of soil and rock materials.As the maximum particle size in the soil and rock materials increases,the width of the gradation becomes wider,and the maximum erosion depth of the soil and rock materials after being washed gradually decreases,and the corresponding horizontal position gradually approaches downstream;when the maximum particle size contained in the particle group is the same,The scouring strength of the soil and rock material without cohesive particles in the granule group is less than that of the soil and rock material containing the cohesive particles;the scouring amount of the non-uniform viscous soil and rock material is as the gradation becomes wider and the maximum particle size increases.Gradually become smaller;when the wide-graded soil and rock material with large particle size is washed by water,the large particle size exposed to the surface during the scouring process reduces the intensity of the water flow,weakens the near-low flow velocity,and prevents the smaller particle size at the same time The movement of the particles protects the bed surface,and the wider the gradation,the more obvious this phenomenon.(2)The influence of the flow process on the erosion and transportation of widegraded soil and rock materials.For uniform soil and rock materials,the larger the peak flow value of the test flow process,the smaller the maximum vertical erosion depth of the soil and rock materials,and the smaller the value of the maximum siltation thickness downstream.Under the action of non-constant flow,the scouring amount of earth and rock materials is much greater than that under the action of constant flow.The larger the peak flow rate,the closer the position of the vertical maximum erosion depth of the soil and rock materials by the water flow is to the upstream.The stronger the non-constancy of water flow and the greater the peak flow rate,the more obvious the erosion of soil and rock materials,and the greater the amount of erosion produced.(3)The influence of outflow conditions on the erosion and transportation of widegraded soil and rock materials.The unobstructed downstream discharge conditions make the vertical erosion depth of the upstream accumulation section relatively large,the soil and rock materials are seriously washed,the tail gate opening is small,the discharge flow of the water in the flume is small,and the soil and rock materials are washed to a lesser degree.The overall vertical scour depth is that when the tailgate opening is large,it is scoured severely by water currents,and when the tailgate opening is small,it is weakly scoured by water currents.(4)Theoretical analysis of the initiation of sediment particles.Based on the characteristics of the wide-graded particles of heterogeneous soil and rock materials,an expression formula for the exposure degree suitable for the graded particles is proposed.Based on the scouring process of the flume experiment and the analysis of the scouring results,the bed bottom slope,the longitudinal exposure angle and the lateral exposure angle of the sediment particles are introduced into the sediment particle conditions,and the sand particle rolling mode is established to include the bed bottom slope and sediment particles.The vertical exposure angle and the horizontal exposure angle of the sediment particles start formula.Using the existing formula and the actual starting velocity of the sediment particles measured by the predecessors,a comparative analysis is carried out,and the sensitivity of the formula is discussed.