Study On The Effect Of Particle Shape And Gradation Characteristics On The Particle Fluidity Based On The Granular Column Test

The debris flow of high-speed landslide is a common geotechnical disaster phenomenon,in which high steep and dangerous rocks move downward in the form of debris flow at high speed after large-scale instability and failure.And the debris particles gradually disintegrate and crushing during the movement.This type of landslide often presents the characteristics of supernormal high speed movement.Many scholars have pointed out that particle crushing resulting in the friction reduction may be the key factor to generate supernormal high speed,but the mechanism is still unclear.Particle crushing will lead to change in particle properties such as particle shape and gradation characteristics,which will affect the flow characteristics of the debris flow.From this point of view,based on the granular column collapse test,this paper conducts research on the influence of particle shape and gradation characteristics on the fluidity of particle bodies,which can be used for reference and finally reveal how the change of particle properties caused by particle crushing can promote the drag reduction mechanism of debris flow.The main research contents and conclusions are summarized as follows:(1)Discrete element numerical simulation and laboratory experiments were carried out for the influence of the aspect ratio of the granular column collapse on the flow characteristics.Through mutual confirmation and comparison with other literature conclusions.On the one hand,the validity of the discrete element numerical simulation in this paper is verified.On the other hand,it is found that the flow distance(mobility)of the granular collapse column is closely related to the critical aspect ratio: when the aspect ratio is smaller than the critical aspect ratio,the mobility and aspect ratio have a linear relationship,otherwise a power law relationship.(2)Particle shape is often described by sphericity,angularity and roughness.The effects of sphericity,angularity and roughness on the fluidity of granular columns are studied by using discrete element numerical experiments.The results show that: the mobility of the granular collapse column increases gradually with the increase of particle sphericity and the decrease of angularity and roughness.And the meso-mechanism(mainly including energy conversion and the average coordination number evolution)of the increase of mobility is revealed from the particle level.(3)The gradation characteristics of particles mainly include the inhomogeneity of particle size distribution and the average particle size.The effects of these two aspects on particle fluidity were studied by discrete element numerical and laboratory experiments.The results show that in the case of specific water content(<20%),inhomogeneity has little effect on particle fluidity,while with the increase of average particle size,particle fluidity gradually decreases,which is closely related to the increasing inter-particle occlusal interaction.For the particles with specific gradation,the fluidity decreases with the increase of water content.