09-04-2012, 01:25 PM
SHAFT SINKING
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General aspects of shaft sinking
Mine shafts are not just holes or pits in ground. Although, they may be called ‘pits’, shafts are properly equipped, since they have several important jobs to do. Also, shafts are built, that is sunk, with precision; and their shapes, sizes and sites have to be carefully chosen beforehand.
Job shafts link the surface or ‘pit-top’ and the underground or ‘pit-bottom’ part of a mine.
What shafts do ?
Shafts, being links between pit-top and pit-bottom, have several important jobs to do:
WINDING
Providing ways for coal to be raised.
Providing ways for men to be lowered and raised.
Other winding (Supplies, machines, ponies etc.)
PUMPING
Holding pipes for water which is pumped out of the mine for disposal.
Holding pipes for water which is taken down the mine for fire fighting, dust suppression, drinking water for ponies.
POWER
Holding pipes for compressed air which is forced down the mine.
Holding cables for electricity which is taken down the mine.
Cage chains:
There are six chains: either each chain taking its share of load, or the four corner chains carrying load – with the two middle chains remaining slack ready to take a share of the load should a corner chain break.
Distributing plate:
The chains are held over a cage by distributing plate which brings their upper ends together.
Detaching hook:
This is so made that when it strikes the sides of the detaching hook plate in the headgear its jaws open at the top, releasing the rope with its capel; at the same time sprouts projections on its sides and hold the cage on the plate.
Rope capel:
This is a clamp, the lower end of which is connected to the detaching hook; its upper end grips the rope. There are several types of capels, but in all of them the grip on the rope is so arranged that it tightens as the load pulls.
Shaft sinking with cement injection of strata
Cement injection is effective for strong fissured rocks. It is not suitable for quick sand.
Cement injection may be done from the surface or in stages from the bottom of the shaft being sunk. If holes are drilled from the surface 10 to 15 holes 0f 100 mm dia are drilled with special rigs for the full depth of fissured rock.
If holes are drilled from the bottom of the shaft larger number of small dia holes says 15 to 30 holes of 50 mm dia are drilled with help of heavy rock drills. For cement injection in stages each stage is of 15 to 20 m depth. While injecting from shaft bottom it should be insured that shaft is provided with a strong lining and a concrete plug at the base.