9781439834220.ch13

In highly stressed burst prone ground an ore pass

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Unformatted text preview: rs with the problem of placing ground support in the raise and such raises with a smooth circular configuration is more prone to hang-ups than a rectangular raise that has been drilled and blasted. In highly stressed, burst prone ground, an ore pass usually has to be raisebored for safety reasons. The same reasons make placing ground support in the raise problematic.16 13.13.1.2 Ore pass lining In bad ground, ore passes are often lined with concrete. In many cases, the concrete is faced with high strength steel liner that also provides the formwork that is required to pour the concrete. The steel lined ore pass has proven its suitability worldwide; however, the high cost and time required often make this design impractical.14 Different means have been developed for placing a concrete lining to reduce the cost. It is generally accepted that the resistance to wear of concrete and shotcrete is mainly dependent on the aggregate employed. It has been proposed that the most economical procedure is to select an aggregate material that has a relatively high abrasion resistance and toughness, such as: basalt, Andesite, diabase, diorite, etc. or some metamorphosed trap rocks. The method has proven effective in South Africa and at some locations in North America; however, the high price of the special aggregate makes it cost-prohibitive for most applications. In hard rock, a long glory hole is not normally lined. Instead, two glory holes are provided near the same location for the following reasons. ● ● ● Lining a long glory hole properly is more expensive than drilling the hole. A second raise provides the required relief to exhaust the air blast (when both raises are inter-connected). If one raise becomes inoperable, the second one is available. 13.13.1.3 Design consideration of rock pass/ore pass5,12 In figures 13.12(c) to (f) orepasses of different designs have been presented. Figure 13.12(c) illustrates the ore pass with midway knuckle and figure 13.12(d) an orepass with knuckle at bottom. In figure 13.12(e) an inclined orepass with inspection raises © 2005 by Taylor & Francis Group, LLC 352 SURFACE AND UNDERGROUND EXCAVATIONS D D (a) (b) in θ DS H L n r n r r Mechanics of ore flow in orepass system (Pfleder et al. 1961) W Side wall forces n r w (γ, φ, c, H, D, θ) (γ, µ, c, φ, H, D, θ) (γ, H, D) n Arching forces these result from complex relationship among all variable r w θ θ n Symbols γ − Weight/unit volume µ − Friction factor of ore and wall φ − Angle of internal friction c − Cohesive strength 60° IR/D 200–300m 160 m Chute Car (c) Orepass with (d) Orepass with midway knuckle knuckle at bottom (e) Inclined orepass with (f) Vertical circular inspection raises and drifts orepass Figure 13.12 Mechanics of ore/rock flow in vertical and inclined passes. and drifts have been shown. Orepass shown in figure 13.12(f) is a vertical and having dia. of 9 m. These ore passes are fitted with chute gate of different types so that ore flow from them can be controlled and regulated to feed dir...
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