Depillaring with stowing (Bord & pillar)

As in the case of depillaring with caving, pillars which have been "robbed" should be stabilised in the depillaring district by sand stowing. The pillar to be extracted is split into 2 or 4 stocks depending upon its size. Coal cutting machines may be used for the purpose. The operations are conducted from dip to the rise in a panel. In each stook splits are driven either with coal cutting machine or manually and the size of split is normally 3 to 4.8 m. Between two adjacent splits a rib of coal, 1 to 1.5 m wide, is kept solid. At one time only one split (and sometimes two) is started in one stook and when that split is about to be completed, the second split is started in the same stook with a view to keep coal production nearly non-fluctuating. The split which is completed is then stowed with sand.

When the second split of the same stook is completed and the place is ready for stowing, coal from the partition-rib is extracted to the maximum possible extent before stowing. The operations are so conducted that not more than 80 m² of roof area is exposed in any working place at a time and not more than two such areas are left unstowed at any time. Fig. 10.6 shows the general arrangement. It may be noted that sand stowing pipes are taken to the depillaring area from the main pipe by branches at two or three places for facility of stowing. The figure shows a diagonal line of face, but a line of face parallel to the dip-rise may also be followed. A line of face parallel to the dip-rise is common and this helps stowing operations which are commenced at the dip end of the boxing. Fig. 10.7 shows a line of face parallel to the strike.