139 blasthole raising method long hole raising this

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Unformatted text preview: brakes control the speed of the unit. 13.9 BLASTHOLE RAISING METHOD: LONG-HOLE RAISING This method15 consists of drilling long-parallel holes in a cylindrical or burn cut pattern. The hole length and inclination is kept the same as that of the intended raise to be driven (fig. 13.4(d)). In order to adopt this technique two levels (i.e. the top and bottom of the raise) must be available. From the upper level down holes are drilled to get through into the lower level. On completion of drilling, the blasting is undertaken in stages as shown in figure 13.4(d). Raises driven by this technique are having inclinations exceeding 50° to vertical. In order to carry out drilling the pneumatic or hydraulic drifters mounted on the pre-fabricated rigs or vertical columns and horizontal bar structures are used. The former type of mounting requires an extra space all around the raise configuration equal to 0.75 m to 1 m to accommodate the equipment. When drifter is mounted on jack type vertical column and horizontal bar structure, it gives accuracy and flexibility while drilling the holes in any position and angle. This type of structure also needs a clear space of 0.5 m from all sides of the raise at the drilling site. All the components being © 2005 by Taylor & Francis Group, LLC EXCAVATIONS IN UPWARD DIRECTION – RAISING 341 lighter in weight than rig mounting, shifting them from one site to another is quicker, hence, use of this type of mounting is very common. The holes drilled are from 50 mm to 100 mm dia. In practice, the steps outlined below are followed: Marking the raise To begin with, the surveyor marks the center point; raise boundary and its intended direction at the drilling site (locale or face). Then the site should be inspected by the driller and the supervisor to check for its suitability to install the drilling equipment with respect to its height and necessary clearance required for the machine to run effectively. The site is then cleaned, floor is checked by the blaster, the service lines are brought up to the site and drill pattern is marked at the back of the raise face and not at the floor to avoid its obliteration. Equipment installation At the site the drilling rig is brought and installed. If column and bar mounting is used the jacks must be perfectly tightened against the roof. Drilling Drifter drills, with the mountings, as discussed in the preceding paragraphs, are used to drill the holes up to 100 mm dia. The holes are drilled either in burn cut or cylindrical cut patterns (fig. 13.8, also refer fig. 9.4). In the cylindrical cut pattern, few cut holes (may be from 1 to 3) of large dia. (upto 100 mm or so) are required to be drilled. This can be achieved by reaming the normal size holes. But in burn cut all holes’ dia. is kept the same. Placement of the holes in any of these patterns should be such that there is minimum time required while shifting the machine from one hole to another, as shown in figure 13.8. Total number of holes shown in this figure is for a mine in which this practice was new but these numbers can be reduced, and any of the desi...
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This document was uploaded on 02/12/2014.

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