Image processing algorithm for systematic evaluation of angle of repose and void ratio for particulate media

The angle of repose is a simple yet helpful parameter to evaluate the frictional response of particulate media. Due to its importance, multiple scientific and engineering fields rely on the angle of repose for strength, storage, and transport calculations. Techniques to measure the angle of repose mostly rely on manual measurements, which do not typically include the associated packing of particles. To expand the use of these measurements, we developed a new image-processing algorithm that measures the angle of repose and calculates the void ratio. The algorithm uses digital images obtained in a transparent rotating cylinder and the Radon transform to locate the position and direction of the repose surface so that the angle of repose can be measured and the void ratio can be calculated. We assessed and validated the proposed algorithm by testing particulate media mixtures made of different volume fractions of crushed glass particles and glass beads. As expected, as the volumetric contribution of the glass beads in the mixture increases, the measured angle of repose decreases (i.e., the angularity of the mixture decreases), and the void ratio decreases (i.e., particles can pack closer together). We expect that the systematic use of the proposed technique and the particle shape analysis can help rapidly estimate critical state soil parameters.