Hypergravity Scaling Laws And Disaster-causing Mechanism Of Size-segregation In Bi-disperse Granular Flows

Particle size segregation is a common occurrence in debris flows,making it important to study its impact on the movement and impact characteristics of landslides and debris flows to prevent geological disasters.Precise collection of stream-wise and depth-wise velocity data is crucial for macroscopic and microscopic analysis.Existing research based on discrete element method(DEM)lacks micro-data calibration and quantitative comparative experiments,and while particle image velocimetry(PIV)is commonly used to collect particle velocities,it cannot accurately analyze changes in depth-wise velocities of different particles.Hypergravity experiments can reproduce the prototype stress field,but scaling laws of particle segregation in bi-disperse granular flows still need to be studied.This article addresses these issues by conducting flume experiments using particle tracking velocimetry(PTV)to study segregation and impact characteristics of particle flow under different impact distances.Using Particle Flow Code 3D(PFC3D),a DEM numerical model is established and calibrated with experimental data to study the macroscopic and microscopic flow behavior and impact characteristics of bi-disperse granular flow during the segregation process.Through dimensional analysis,a basic motion scaling law of bi-disperse granular flow under hypergravity field is derived,verified with DEM numerical method,and extended to segregation motion and impact process.The main conclusions of this paper are as follows: Firstly,in terms of macroscopic motion behavior,the flow direction of particles in a bi-disperse system is faster than that of a monodisperse system of corresponding components,and the normal velocity is more disordered.In terms of meso-kinematic parameters,the Fr number of particle flow in a bi-disperse system is larger than that in a monodisperse system of corresponding components,indicating a stronger flow,while the inertia index I is smaller and energy dissipation is lower.Regarding impact characteristics,the impact of bi-disperse particle flow on a rigid baffle is the most significant.Among the corresponding components,the impact of larger particle flow on the rigid baffle is smaller,and the impact of smaller particle size is the smallest.Secondly,when the ratio of particle size in the bi-disperse granular flow increases,the segregation time of the bi-disperse particle flow decreases,and the degree of segregation increases.The maximum impact force of the bi-disperse granular flow with a larger segregation coefficient on the rigid baffle is greater,the resultant impact force is higher,and the bending moment of the baffle is larger.This means that debris flow of landslides with higher particle size dispersion has stronger disaster-causing characteristics.Finally,through theoretical deduction and numerical simulation,the scaling law under hypergravity field is found to be applicable for particle size segregation in bi-disperse systems.