Study On Velocity-deceleration And Volume-reduction Mechanism Of Arc-shaped Submerged-sill Against Granular Flow Along Narrow And Steep Gully

Granular flow or debris avalanche in steep-creeks is a catastrophic hazard to the residential lives and properties in the mountainous areas.It has the characteristics of fast speed,great impact,long movement distance,great harm and severe disaster,which seriously affects the security of life and property safety of residents lives in the mountainous areas.At present,the rigid barriers such as baffle piles were embedded the stable bedrock in the channel produce a promising mitigation effect.However,these rigid barriers structures often fail due to extreme impact force or reservoir filling.As a commonly used prevention and control measure of Granular flow or debris avalanche in mountainous areas,the multiple array of submerged sill with a smaller dimension and stronger impact resistance can also reduce the volume and velocity of the avalanche and dissipate the kinetic energy.Meanwhile small mining equipment can be used for timely cleaning after each siltation.However,there is still a lack of quantitative research on the effect of sill geometry and height on sill energy dissipation.Therefore,this research takes debris avalanche in steep-creeks as the research object,based on the submerged sill structure,combined with physical model experiment and numerical simulation,and analyzes the velocity-deceleration and volume-reduction of submerged sills with different shapes and heights to debris avalanche in steep-creeks.This research helps us to reduce the sliding distance of debris avalanche in steep-creeks,reduce the enormous kinetic energy of debris avalanche,improve the prevention and control measures of debris avalanche,and provide reference for the prevention engineering.The main contents of this paper are as follows :Firstly,based on the self-designed chut experiment,the physical model experiment of the interaction between the submerged sill and the debris avalanche was carried out by using the submerged sill with different shapes and heights and quartz sand particles with different fractal dimensions.The deceleration and decrement effects of the submerged sill on the debris avalanche under different combinations of factors were emphatically analyzed.The high-speed camera is used to capture the motion state of the debris avalanche when passing through the submerged sill.The PIVlab software is used to calculate the velocity of the debris avalanche.The Context Capture Center software is used to collect and analyze the three-dimensional geometric shape of the accumulation body.Based on the physical model experiment,PFC3 D was used to conduct the numerical simulation test of the interaction between the submerged sill and the debris avalanche.The influence of the shape and height of the submerged sill on the motion characteristics of the debris avalanche was studied,and the impact energy dissipation mechanism of the submerged sill structure was revealed.The main factors affecting the energy dissipation of the submerged sill were proposed.This paper mainly draws the following conclusions :(1)Under the influence of dispersion pressure and collision pressure,the debris avalanche accumulation has sorting effect.The coarse particle concentration area appears at the front end of the accumulation,and the fine particle concentration area forms at the tail end of the accumulation.(2)In terms of energy dissipation,compared with the condition without submerged sill,the arc submerged sill l reduces the peak kinetic energy of debris avalanche by 13.85%,the rectangular submerged sill reduces the peak kinetic energy of debris avalanche by 7.49%,and the triangular submerged sill reduces the peak kinetic energy of debris avalanche by 10.37%.Under the conditions without submerged sill,arc,rectangle and triangle submerged sill,the centroids of the accumulation body are 45.5cm,23.7cm,27.0cm and 24.9cm,respectively,and the farthest motion distances are 87.1cm,53.5cm,55.0cm and 58.2cm,respectively.Submerged sill energy dissipation effect: arc> triangle > rectangle.In terms of reduction,under arc,rectangular and triangular submerged sill conditions,the mass of particles captured by submerged sill is 0.014 kg,0.018 kg and 0.008 kg,respectively.The reduction effect of submerged sill is rectangular > arc > triangle.(3)In terms of energy dissipation,compared with the first row of submerged sills,the reduction rates of the second row of submerged sills on the farthest motion distance of debris avalanche,centroid motion distance and accumulation area of accumulation body are 2.3%,10.5% and 1.95%,respectively.When the submerged sills are arranged in multiple rows,the projection angle formed when the debris avalanche passes through the submerged sill should be fully considered.If the influence of submerged sill spacing is not fully considered,the second row of submerged sills will be wasted.(4)With the increase of submerged sill height,the reduction effect of submerged sill on the farthest motion distance,centroid motion distance and accumulation area of debris avalanche increases gradually.Considering the farthest motion distance,centroid motion distance,accumulation area,internal motion difference and internal diffusion difference of debris avalanche,it is found that the arc submerged sill has the best reduction effect on debris avalanche energy under the condition of h = 4cm,and the peak kinetic energy of debris avalanche is reduced by 21.0%.