Laboratory investigation of dry granular flow through an opening

Granular flow is a scientific problem with applications in many engineering problems such as sinkholes, ground surface collapse, and soil loss into a defective pipe. In most previous studies, however, only single size grain has been considered in mass flow rate calculations for simplicity. In nature, most granular materials have different sizes of grains. It is believed that the grain size distribution plays an essential role in the flow mechanics of granular material, which has not been well studied. This study investigates the effects of the grain size distribution on the granular flow through a slot experimentally. It also examines the development of a free-fall arch during the flow process. The results show that the grain size, grain size distribution, and slot width are the controlling parameters that determine the mass flow rate. The mass flow rate is found to be independent of the material height above the slot for any given grain size distribution. This observation suggests the existence of a free-fall arch that controls the flow rate above the slot. Besides, the mass flow rate is governed by the finer portion of the material rather than the coarser materials. In calculating the mass flow rate using the existing formula, there are some discrepancies between the calculated and observed flow rates which are attributed to the simplifications in the formula, which does not consider the effects of grain shape and flow density. An attempt is made to identify the characteristic grain size based on experimental measurements for non-uniform grain size distributions to calculate the mass flow rate.