William McBride

This paper presents a design, and a design method, sufficient to engineer a passive solution to the problem of discharge bias resulting from tonnage fluctuation with soft loading transfer chutes. This is achieved by considering the momentum change inherent in the bulk material stream through the hood section of a soft loading transfer point. This momentum change is utilised to move the hood in a predefined path to ensure the discharge centroid remains consistent.The majority of soft loading transfer points are between conveyor belts that include a plan view change in the material direction which immediately impacts on the design of the transfer point. This impact is, the designer must optimise the transfer for a narrow bandwidth of throughput to achieve optimal outcomes or else accept the potential for mis tracking on the receiving belt. This is due to variations in throughput tonnage altering the location of the discharged materials centroid from a fixed hood section, resulting in a tendency for the receiving belt to mistrack due to biased loading.

It has been shown (McBride, 2006 McBride , W. 2006 . Base pressure measurements under a scale model stockpile . Part. Sci. Technol. 24 : 59 – 71 . [Taylor & Francis Online], [Web of Science ®] [Google Scholar] ) 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.

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 Jotaki , T. & R. Moriyama . 1979 . On the bottom pressure distribution of the bulk materials piled with angle of repose . J. Soc. Powder Technol. Jpn. 60 : 184 – 189 . [CSA] [Crossref] [Google Scholar] ; Lee & Herington, 1971 Lee , I. K. & J. R. Herington . 1971 . Stresses beneath granular embankments . In Proceedings of the 1st Australia- New Zealand Conference on Geomechanics . Sydney: Institution of Engineers . 1 : 291 – 297 . [Google Scholar] ; Smid & Novosad, 1981 Smid , J. & J. Novosad . 1981 . Pressure distribution under heaped bulk solids . In Particle Technology: Proceedings of the 1981 Powtech Conference . Rugby : Institution of Chemical Engineers . D3V 1 – 12 . [Google Scholar] ), 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.