William McBride

Base Pressure Measurements under a Scale Model Stockpile

ABSTRACT The ability of a granular bulk material to transmit internal shear stress is a fundamental property that is often overlooked or underestimated, yet it is this ability that allows many observed physical phenomena to occur. One such area that continues to be a focus for numerical, theoreticals and experimental researchers is the pressure that a stockpile of granular material places on the supporting surface. While appearing to be a simple problem, the ability of granular materials to transmit shear stress makes this an extremely complex problem. This article presents high-quality data collected under a 2 m high stockpile and full details of the experimental facilities used in the collection of the data. The work presented is of significant value, having a much greater scale than previous studies (Jotaki & Moriyama, 1979; Lee & Herington, 1971; Smid & Novosad, 1981), and the deliberate inclusion of a central reclaim channel offers insight into stress changes during gravity reclaim and refilling. The results of this work have shown that the so-called ‘M’ pressure does exist under larger stockpiles both with and without reclaim hoppers; of more significance is the reemergence of the M pressure upon refilling of an emptied stockpile. This clearly illustrates that the M pressure is a robust and natural pressure distribution for a conical stockpile.

A New Approach for Calculating the Mass Flow Rate of Entrained Air in a Freefalling Material Stream

This article presents the outcomes from a series of physical experiments to measure the air entrainment rates encountered within a stream of freefalling particles. The experimental work presented spans a range of particle parameters and hopper geometries. From these results a new theory for the prediction of air entrainment is developed and presented. This new method was developed specifically to facilitate a better understanding in the area of fugitive dust control associated with material handling systems, which are driven by the air entrainment during freefalling. From the work presented in this article, a better prediction capability of freefalling bulk materials in either constrained, or unconstrained systems, will allow for the optimization of either passive or active dust control strategies. This article presents several distinct sections that detail the experimental work used to determine the freefall stream parameters that were conducted to allow the development of the entrainment equations.

Base Pressure Measurements under a Scale Model Stockpile: Effects of Offset Reclaim Channels and Predictive Model Developments

It has been shown (McBride, 2006) that under a scale model stockpile a central pressure dip, or ‘M’ pressure, is formed during both the filling and refilling processes of a stockpile containing a central reclaim channel. This article presents the results from further experiments with a noncentral reclaim channel and clearly illustrates that a central pressure dip exists under a conical stockpile with an offset reclaim channel. Additional data were recorded regarding lateral load transfer within the stockpile on initiation of flow, although more experimental work is required to fully understand this aspect. A method for predicting conical stockpile base pressures is presented along with an overpressure theory to account for the vertical load instability induced by the onset of material discharge.