Proposal of Sidewall Velocity-Controlled Cylindrical Angle of Repose Measurement Apparatus

When it is attempted to study the angle of repose, there immediately emerges the fact that the inclination angle of a sand heap is not constant. Sand heaps exhibit two angles: one at which they begin to collapse after reaching a certain slope, and a smaller angle at which the collapse settles down. This shows that even when perfectly stationary, a sand heap can have an inclination angle between these two angles. Therefore, many experiments are required to determine the angle of repose from varying inclination angles of a perfectly stationary sand heap. In this study, a new sidewall velocity-controlled cylindrical angle of repose measurement apparatus was developed that can continuously capture images of sand heaps using two orthogonal cameras. By continuously photographing the sand heap, it is possible to register the deformation of the sand heap from the angle at which it begins to collapse to the smaller angle at which it settles down in one experiment, as well as to measure the varying inclination angle. In this article, the angle of the sand heap was measured for sand of different grain sizes from the time it formed to the time it came to rest using the developed apparatus. As a result, it was found that when the sand heap reaches a limiting height, the height thereafter slightly increases and slightly decreases repeatedly. The angle of repose measured while the sand heap was at rest was assumed to be the inclination angle of the sand heap at some point between the critical angle and the angle of rest. By using this experimental apparatus to continuously acquire and average the inclination angles of sand heaps that reach a certain height, it was possible to obtain a highly accurate angle of repose with a small number of experiments.