Fundamental study on the effect of grain size distribution on angle of repose

¹ University of Yamanashi, Graduate Faculty of Interdisciplinary Research, 4-4-37, Takeda, Kofu, Yamanashi, 400-8511, Japan
² Yamaguchi University, Graduate School of Sciences and Technology for Innovation, 2-16-1 Tokiwadai, Ube, Yamaguchi, 755-8611
³ Tokyo Electric Power Services Co, Ltd. Research and Business Incubation Unit, 9F, KDX Toyosu Gransquare, 1-7-12, Shinonome, Koto-ku, Tokyo 135-0062

^* Corresponding author: skajiyama@yamanashi.ac.jp

Abstract

In this study, the authors developed a new sidewall velocity-controlled cylindrical angle of repose measurement apparatus that can capture images of a sand heap continuously using two orthogonal cameras in order to reduce the cost of photography. The developed apparatus was used to measure the angle from formation to repose of sand heap using different grain sizes distribution and to assess the effect of grain size distribution on the angle of repose. The formation process of the sand heap was continuously measured using the experimental apparatus, and it was found that the sand heap became steady state when it reached a certain height. It is inferred that the angle of repose measured in a stationary state indicates the inclination angle of the sand heap at a certain point in time, suggesting the possibility of obtaining a highly accurate angle of repose with fewer experiments by using this experimental apparatus to continuously acquire and average the inclination angle of a sand heap in a steady state. For samples with a stepped grain size distribution, the angle of repose was found to be higher than for samples with a gentle grain size distribution at the same 20% grain size D20 and mean grain size D₅₀. It was found that the angle of repose increased logarithmically with increasing coefficient of uniformity. Based on these results, it is clear that for a well-graded sand, it is the grain size rather than the coefficient of uniformity that has an effect on the angle of repose.