| Granular materials are ubiquitous, but we lack a fundamental understanding of their properties. The problem is two-fold as quantitative experimental investigations are scarce and a comprehensive theory describing their various properties does not exist. In this dissertation, I present the results of experimental studies of the flow, instability, and segregation of granular materials in order to obtain quantitative data to test and develop theories.; First, I investigate the flow of dry granular materials inside a quasi-two dimensional silo that is draining from an orifice at the bottom. The boundary between static and flowing regions and the velocity distribution of the grains are investigated and observed to be consistent with the existing phenomenological models. At low flow rates, the surface is observed to be inclined at the angle of repose. However, a hydraulic jump is observed at the surface at high flow rates. I show that it is a shock, and give an explanation for its occurrence. I also show that size separation occurs at the surface, when multi-sized particles are used.; Second, I investigate the stability and segregation properties of wet granular materials by pouring the grains into a silo. In this case, the presence of capillary bridges provides additional forces besides hard-core repulsion and friction. The angle of repose of the resulting pile increases rapidly with the addition of a small amount of liquid and then saturates depending on the viscosity of the liquid. If the particles are bi-disperse, size separation is observed to correspondingly decrease. By using a horizontally rotated drum half-filled with wet granular matter, I also observe that the maximum angle of stability reached just before an avalanche increases with the viscosity of the introduced liquid. Using a series of experiments and estimates, I argue that the creep relaxation and the change of the number of liquid bridges between particles may be the reason for the observed effect. |
