Sides can be rock bolted and lined in the incompetent

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Unformatted text preview: er. Rest using Dresser Raise Borers13 (1 ft © 2005 by Taylor & Francis Group, LLC 0.3048 m). 350 SURFACE AND UNDERGROUND EXCAVATIONS ● ● grounds it has been driven successfully. Sides can be rock bolted and lined in the incompetent formations. Productivity: The process in not cyclic but a continuous one, thereby, in the grounds suitable to this technique faster rate of raising can be achieved. Economical: If enough sites are made available so that utilization of this unit is maximum; it proves to be economical. Due to above listed merits, this method is getting popularity and contractors are using for their civil and construction projects, as outlined in section 13.1. 13.12 RAISE BORING IN A PACKAGE – BORPAK6 It is a recent addition to the raising techniques.6 This unit is self driven and mounted on crawler track. It is used for blind raising. This unit is set up underneath the intended raise (fig. 13.11),6 and starts boring upward through a launching tube. After the head has penetrated a few meters into the rock, grippers hold the body while the head rotates and bores the rock similar to the tunnel-boring machine. It can bore blind raise of 1.2 to 2.5 dia., up to 300 m lengths. 13.13 ORE PASS/WASTE ROCK PASS5,12,16 Passes are openings that are driven in the rock massif for conveyance of waste rock, ore, filling material from the upper levels (elevations) to the lower horizons (elevations). Gravity assists to the flow of material. Such openings are an integrated part of the ore and waste rock movements in the modern mines. These passes are also useful for deep seated open pit mines where the rocks are hauled up or down through such openings for their onward disposal (fig. 17.16(e)). Size and shape They can be driven with the application of raising methods, with or without aid of explosives (fig. 13.2). However, the method selected should meet the objective. Square, rectangular and circular are the usual shapes. Size of Ore Pass:16 Apart from rule of thumb, and adopting the size based on experience of other mines having almost the same environment; some empirical relations Figure 13.11 BorPak – raise boring machine. © 2005 by Taylor & Francis Group, LLC EXCAVATIONS IN UPWARD DIRECTION – RAISING 351 have been developed based on experience gained at Czechoslovakia mines. In specifying these formulae lump size, size distribution pattern, gradation, stickiness, etc. have been considered. (13.6a) (13.6b) (13.6c) d is the size of largest lump. Value of k is determined from the nomograph. For typical hard rock mines, given below are some of values of “k” under different set of conditions: k k k 0.6 when the content of sticky fines 1.0 when the content of sticky fines 1.4 when the content of sticky fines 0%. 5%. 10%. In hard rocks mines all very fine material (passing 200 mesh) is considered sticky due to water sprayed on it to suppress the dust. A borer driven circular ore pass is more stable than a square or rectangular ore pass. The latter invites arching on the sides and stress concentration at the corners. Circular ore pass made with borer suffe...
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