Study On Granular Flow Propagation And Depositional Characteristics Based On Granular Column Collapse Experiment

Rock avalanche,as an extremely destructive geological disaster,is characterized by tremendous volume,extraordinary high speed,unpredictable run-out distance,huge energy and abnormal mobility.In the major engineering activities of Sichuan-Tibet Railway,Dian-Tibet Railway,China-Pakistan and China-Nepal Economic Corridor,the potentially large rock slides and rock avalanches occurred on Qinghai-Tibet Plateau that present complex geological environment have become major engineering geological problems.Based on the investigation of the anciently giant Tagarma rock avalanche,the physically model experiments of the collapse of particle column and further numerical simulation analyses were carried out for researching of rock avalanche in unconfined environment.By controlling the material conditions of particle flow(particle size,particle size distribution),energy conditions(initial column aspect ratio,initial volume)and terrain conditions(bottom friction coefficient),this study explored the influence of various mainly control factors on paticle flow movement and accumulation.The main findings are as follows:(1)According to the velocity characteristics during movement of particles,the process can be divided into: vertical collapse stage,the leading edge spreading stage,rear edge side slip stage;furthermore,the vertical collapse stage can be subdivided into creep deformation stage,collapse stage and shear slip stage.(2)The curve of particle velocity evolution on the leading edge consists of several locally pulsed peaks with same evolutionary form.Under the same particle size and particle size level,the number and peak strength of local velocity peaks showed positive correlation law with energy conditions.Under the same initial column aspect ratio and volume,the number of local velocity peaks was the same,and the peak intensity changed with the positive correlation law of particle size,and firstly increase and then decrease with the increase of fractal dimensions.(3)From source area to accumulation zone,the interaction intensity between particle flow and the base plate gradually weakened.The evolution curve of the stress fluctuation at the base increases when the large particles increases.Besides,the peak strength of the base pressure is positively correlated with the content of large particle size,initial aspect ratio and initial volume.(4)The surface of the accumulation present accumulation platform,longitudinal ridge,transverse ridge,pile mound and other sedimentary landscapes,which are arranged regularly in space and those fluidized more visible with the decrease of particle size under single-particle particle flow.The location of large particle size on the surface of the multisized particles accumulation body is consistent with the location of lateral ridges,longitudinal ridges and lateral embankments in the singlesize particles accumulation(5)The initial height to width ratio and initial volume are the main factors affecting the stacking morphology;Under the condition of equal particle size and gradation,the coverage area of dense accumulation area is positively correlated with the initial column height width ratio and initial volume,and the growth rate gradually decreases.Under the condition of equal aspect ratio and equal volume,with the increase of the content of large particles in the particle flow,the scattered particle accumulation area develops in the front of the accumulation body.When the average particle size of single particle flow increases,the coverage area of dense particle accumulation area first increases and then decreases;When the fractal dimension of multi particle flow increases,the coverage area of dense particle accumulation area first decreases and then increases.The roughness of the underlying terrain only affects on the particle flow of large particle size,which present that the depositional area linearly decrease with the increase of the coefficient of friction.(6)From the internal characteristics of the accumulation,the preservation of initial stratigraphy sequence formed in the single-size particle flow.The observation of the mixture of particles increasing with height indicate that the internal deformation increase from the bottom to top in particle flow.In addition,inverse sorting that large particles segregate upward and fine particles move down also observed on the profile of multisized particle flow.