In this study, the geometrical effects of vertical ore passes contributing to ore pass hang-ups were simulated by 3D discrete element method (3D-DEM). DEM is a method of calculating the movement of each discrete element in an analytical region and is suitable for simulating the movement of ore in an ore pass. Here, two types of cross-sectional shapes of vertical ore passes are assumed: circular and square. These ore passes are initially filled with discrete elements, and the ores are then extracted from the bottoms of the vertical passes. In our analysis, the conditions which cause ore pass hang-ups were evaluated, and the effect of the cross-sectional shapes and the possibility of the ore pass hang-ups were discussed. Results showed that cohesion exerted a strong influence on the occurrence of hang-ups. Moreover, the conditions under which hang-ups consistently occur were determined. In addition, the results showed that the hang-up conditions of circular ore passes were more severe than those of square ore passes and that square ore passes were preferable for avoiding hang-ups.
More than 200 limestone mines are operative in Japan, most of which are located on mountainsides (Limestone Associate of Japan website). Therefore, vertical ore passes are commonly used to transport ore to industrial sites and shipping sites (Fig.1), meaning ore pass hang-ups are a serious problem (Hadjigeorgiou, 2007), and can cause extensive damage during mining operations. Thus, effective methods and designs to avoid from ore pass hang-ups are crucial. In general, circular cross-sections of vertical ore passes are widely used; however, other cross-sectional shapes have recently been introduced. Nevertheless, the degree to which ore pass hang-ups can be avoided remains unknown.
In order to investigate the mechanism of this phenomenon, Sato and Obara (2014, 2015) conducted numerical simulations by 2-dimensional discrete element method (DEM), which is a method for calculating the movement of each discrete element in an analytical region and it is suitable for simulating the movement of ore in ore passes. In that study, the cohesion between ores and ore pass walls was revealed to be the dominant factor in causing ore pass hang-ups in vertical ore passes. However, these analyses were conducted using 2-dimensional model. Thus, the effect cross-sectional shape was not considered.