Alan W. Roberts’s research while affiliated with University of Newcastle Australia and other places

A wedged plane-flow hopper and horizontal belt feeder is employed to investigate the flow patterns and stress field redistribution at the hopper and feeder interface. The flow patterns are recorded by a high speed camera in conjunction with coloured material layers. The three-dimensional stress field in the feed zone and its influence on the feeder operation are discussed. The vertical stresses acting on the feeder for initial filling and flow conditions are measured along with longitudinal shear feeder loads. The experimental results are compared with theoretical values derived using relevant feeder load theories. The influences of different filling heights and clearance between the hopper bottom and feeder surface on feeder loads are presented. Numerical simulations using the Discrete Element Method (DEM) are carried out additionally to analyse feeder loads at the hopper and feeder interface, with the results being compared with those obtained experimentally.

Feeders play an important role in bulk solids handling operations due to their extensive use in controlling the gravity flow of bulk solids from bins and stockpiles. To ensure efficient feeding, the hopper and feeder geometries are designed as an integral unit. Because of the interaction of two systems, the stress states in the hopper for a feeding system, to some extent, differ from the stress states in an independent hopper without the feeder underneath. The feeder loads are induced by the material directly loading on the feeder and influenced by the stress states in the hopper at the hopper/feeder interface. The vertical pressure at the hopper outlet is generally regarded as the direct cause of the vertical feeder load [1, 2]. Further research through experimental investigations [3, 4] suggested that the calculation based on the major consolidation stress in the hopper provided an improved estimation of feeder loads at the hopper/feeder interface for the flow cases taking account of the redistribution of the stress field in the feed zone. This paper presents an alternative hypothesis in terms of the stress states for flow cases in the hopper at the hopper/feeder interface zone. It was proposed that a combined stress state occurred in the hopper during feeder operation, including a passive stress field and an active stress field at the upper and lower sections of the hopper respectively. The height of the switch of the stress fields is also discussed in this study. The results are compared with experimental outcomes and various theoretical calculations. Notation: Pv0 = Average vertical pressure at hopper outlet (Pa) L = Hopper outlet length (m) D = width of the vertical part of the bin [m] B = average width of the hopper outlet [m] q = Non-dimensional surcharge factor K= ratio of pn/pv for hopper pn = normal wall pressure (Pa) pv = average vertical pressure (Pa) γ = bulk specific weight (N/m 3) hh=distance from apex to the transition of hopper (m) z = depth coordinates from hopper transition (m) hc =surcharge head acting at transition of cylinder and hopper (Pa*m 3 /N) m= symmetry factor, m=0 for plane-flow hopper, m=1 for axi-symmetric or conical hopper α = hopper half angle (°) ϕ = wall friction angle (radians) µ= tan ϕ, coefficient of wall friction δ = effective angle of internal friction [°] kj = pressure ratio in Janssen equation H = the head of bulk solid in cylinder (m) hs = bin surcharge head (m) ps = surcharge pressure from passive stress field in the hopper at distance zh [Pa] ps0 = surcharge pressure at datum transition [Pa] zg = height of the hopper [m] zh = distance from transition at which the passive stress field switches into active stress field [m] khf = ratio of normal wall pressure to vertical pressure in passive stress field η = angle between the major consolidation stress and the normal stress at hopper wall [radians].

The determination of the wall liner properties and more importantly the flow properties of a bulk material is critical for the design of any bulk materials handling system. The design of such materials handling systems will be most effective when handling bulk materials at the physical properties they were designed to handle. Due to the fast-paced nature of expansion in the mining industry and demand of mineral resources, it is quite common for materials handling systems to handle bulk materials that were not intended for the system. Wet and Sticky Materials (WSM) within the materials handling stream can cause significant downtime, due to events such as blockages of bins, hoppers and transfer chutes, remains left in train wagons and dump trucks as well as conveyor belt carry back (Roberts, 2005; Connelly, 2011 [2]). WSM are problematic within the materials handling stream due to the inter-particle and boundary cohesion and adhesion forces. The current measurement techniques for WSM have limitations and new methods must be considered. The development of new testers that can measure the wall adhesion and inter-particle adhesion of a bulk material can give a quantitative value for the adhesion present in a bulk material sample. The following paper will present a revised methodology for the estimation of the adhesion of bulk materials determined from the extrapolation of the Instantaneous Yield Locus (IYL). The predicted adhesion values from this methodology will be compared to experimental measurements using an inter-particle adhesion tester.

Numerical simulations using the Discrete Element Method (DEM) were carried out to investigate the flow patterns and stress field redistribution at the hopper and feeder interface. The influences of different filling heights, belt speeds and clearances between the hopper bottom and feeder surface on feeder loads were studied. Meanwhile, experiments were conducted by utilising wedged plane-flow hoppers with different configurations and horizontal feeders with various clearances. The simulation results were compared with theoretical values and experimental measurements. In terms of the cases presented in this study, simulation results reveal good agreements with experimental observations regarding the flow pattern. Being similar to the theoretical values, the simulations provide close predictions on vertical feeder loads for steady flow states, but they may show significant overestimations for initial states. Additionally, suggestions are given for relevant simulation parameters based on the comparisons shown in this investigation.

The eccentric discharge of bulk solids from a silo can lead to asymmetry in the normal pressure distribution around the silo walls. The non-uniformity and eccentricities of the wall loads, which would cause bending stresses in the circumferential direction at various levels, can have serious structural consequences. Understanding how the wall loads are affected by eccentric discharge is an aspect of silo design of major importance. In this study, the wall loads during the eccentric discharge was investigated by performing a range of DEM simulations for a coal silo with two outlets when only one outlet is in operation. Apart from the information regarding the flow patterns developed during discharge and the corresponding normal wall loads that are generated, the simulations enable an appreciation of the transient flow patterns that occur as the stress fields change from ‘active’ to ‘passive’ states when flow is initiated. Of particular interest are the distributions of the normal pressures around the periphery of the silo wall at a height defined as the ‘critical transition’ where the flow down the wall converges as a result of a “hopper type” flow channel forming above the cylinder/hopper transition. The wall loads distribution has been investigated under two situations, namely, with or without localized dead zones due to build-up of bulk solids within the silo. The DEM results indicate that the wall loads on the side furthest from the eccentric discharge location are larger than those on the side nearest the eccentric discharge location, the results being comparable to those derived from AS3774 (1996) and EN 1991-4 (2006). The DEM results also show the significant variation in the wall load distributions which could affect the structural integrity of the silo. The DEM simulations are also used to explore the effects of particle-wall frictional coefficient.

This paper presents the results of experimental investigations aimed at the determination of the loads exerted on support structures buried in gravity reclaim stockpiles. Structures, such as trestle legs to support load-out conveyors in open stockpiles, or columns to support roof structures and load-out conveyors of enclosed bulk solids storage sheds are subject to the loads exerted by the surrounding bulk solids. The complexity of these loads has been discussed recently (Roberts, 2007 [1], Katterfeld and Roberts, 2009 [2]). According to the theoretical approach proposed by Roberts, both active and passive stress states in bulk solids contribute considerably to the pressure distributions on these support columns. The findings of the preliminary experimental studies carried out by Roberts match with the theoretical predictions. However, follow-up work is required to further validate and improve the design equations for the determination of the loads on support columns. Based on Roberts' prediction model, a laboratory scale test rig was constructed to measure the loads on both the front and rear faces of a buried column. Tekscan tactile pressure sensors were employed in the pressure measurements. Stockpile tests under three different conditions were investigated, and the measured results correlate well with theoretical predictions from modified Roberts' theory. The outcome confirms that Roberts' theory can contribute to the design criterion regarding the loads on buried structures in stockpiles.

Based on Jenike's method, only the self-weight of each arch element is involved in the calculation of the arch thickness parameter which leads to the surcharge pressure not being taken into account in determining the critical outlet dimension of a bulk material storage bin. The aim of this study is to investigate the influence of surcharge pressure on Wall pressure distribution and arching behavior in mass-flow structures. A method is introduced to measure the hopper wall pressure distribution. The measurements of the wall pressure and critical outlet dimension were conducted under different surcharge pressures and at various filling levels. The experimental results are compared with existing prevailing theories, where the theoretical outlet dimensions demonstrated significant overdesign in terms of low surcharge pressure and reasonable estimates corresponding to high surcharge. The peak wall pressures around the transition area of the bin are smaller than the calculated values, whereas the stresses close to the outlet are larger than the relative theoretical values.

This paper presents the experimental results of mass-flow hopper arch geometry investigation, which was conducted using a variable geometry plane-flow bin. The cohesive arches formed under different critical outlet openings and hopper half-angles were measured using a 360° two-dimensional laser line scan system. This system was employed to obtain the complete surface profile of each arch across the width of the outlet by moving the rotating laser along the total length of the outlet. The test results were analyzed using Matlab, adopting stationary wavelet transformation de-noising to decrease the signal noise generated during the testing process. The geometric data for each single line scan was smoothed and combined to present a three-dimensional arch surface profile shown to be in good agreement with the observed experimental arch profiles. The angle η at the intersection of the arch with the hopper walls was then calculated by running a Matlab program and a new angle η' is introduced to the arch shape study. The detailed results are discussed in the paper. Arch geometry models, such as the parabolic arc and circular arc arch models developed, respectively, by Walker [ and Enstad [ are reviewed and their relevance is discussed based on the experimental results presented in this paper.