Exploring the influence of physical properties on the coefficient of restitution (COR) of granular materials

Abstract

Hong Kong is classified as a mountainous region where landslides happen frequently. Debris flow is one of the complex phenomena which involves the interactions between particles of various sizes. This complexity is advanced due to complex morphology and heterogeneous nature of soil. Geotechnical measures provide effective slope management and also mitigation which require insightful information of granular flow. Simulation modelling of granular flows is usually carried out by Discrete Element Method (DEM). Coefficient of Restitution (COR) is an essential input in the numerical analyses of granular flows. It is a parameter describing impact behavior of grains which is defined as the ratio of impact to rebound velocity during a collision of two objects. In this research, the value of COR is determined experimentally for different materials and sizes of interest under various impact velocities using a micro-mechanical impact loading apparatus. In addition, roughness effect on COR is studied via abrading grains. In most of the previous research, engineered materials were being investigated, for which the behavior are predictable due to their homogeneous properties. In this work, Leighton Buzzard sand (LBS) grains were also under investigation and a comparison has been made with engineered glass spheres. A total of 120 measurements were carried out over impact velocities ranged from 1.74 m/s to 2.37 m/s. Complying with kinetic energy equation, results show that COR decreases as impact velocity increases. Size effect on COR was obtained by comparing the results of spheres in 2mm and 3mm diameter dropped on a brass block. Spheres of larger size induced higher kinetic energy loss during collision thus resulted in a decreasing trend in COR. Present results are consistent with previous work either in numerical simulations or experimental studies. Besides, present works are compared with previous works for examining roughness effect on COR.