9781439834220.ch13

5 to 3 m while keeping rest of the hole empty of

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Unformatted text preview: xplosive, equal to the length of round that is usually, 2.5 to 3 m, while keeping rest of the hole empty. Of course to stem it over © 2005 by Taylor & Francis Group, LLC EXCAVATIONS IN UPWARD DIRECTION – RAISING 343 the explosive column; the drilling’s rock cuttings/chips, or some stemming material can be poured into the hole. In non-watery conditions use of explosive ANFO with suitable primer/booster is usually made; as its use gives advantages of ease in charging and low cost. Use of delay detonators is made to achieve sequential blasting. Usually ANFO is poured manually without use of pneumatic loader otherwise electric detonators will have to be replaced by the antistatic detonators Anodets. This is to note that right from the first round itself all the holes should be kept equally empty and at the same level (horizon). Before charging the next round, all the holes should be thoroughly cleaned and blown using compressed air. If some of the holes get jammed due to previous blasting, it is important to get them through, may be sometimes, by blasting their neighboring holes using a mild charge. Once all the holes are through. The same procedure for blasting the subsequent rounds follows. Before blasting, the workers at both levels should be warned and approaches to the raise site (at both levels) should be well guarded. Special care should be taken when the parting to get through into the upper level is 5 m or less. This portion should be taken in one round only to avoid damage to the holes and formation of excessive loose around the raise collar. In this technique, this is how the charging operation is conducted from the upper level, while the blasting progresses upward from lower level towards the upper one. 13.9.1.7 Limitations This technique can be applied only if raise site can be accessed from both the levels. Blind raising is not feasible. Raises upto 40 m lengths and 45° inclinations can be driven. Accurate drilling and proper blasting is the key to the success of this method. Disturbed ground with joints, fissures etc. may result frequent jamming of drill rods and bits. 13.9.1.8 Advantages Safety: This is a noble technique by which man is not required to enter into the raise during its drivage as both drilling and blasting operations are conducted from the upper level only. Productivity: Operation is not cyclic, thereby, better productivity and faster rate of drivage can be achieved. Raise can be drilled in advance and it can be blasted as and when required. Muck removal is not essential after every blast. While drilling is going on at one site, preparatory arrangements including shifting of all fittings other than the drilling equipment can be undertaken at another site. Better working conditions: Workers are required to work at the levels where better working conditions are available comparing the same if they are required to work within the raise in a limited space and under the some arduous conditions that prevails with the other raising methods. This technique is specially beneficial in the areas of bad ground and...
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This document was uploaded on 02/12/2014.

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