Sizes of pillars and galleries (coal)

The width of the road varies from 3 m to 4.8 m, 4 m width being common where coal cutting machines are used. The height varies from 2 m to 3 m, nature of immediate roof being the deciding factor. Under the coal mining Regulations the gallery in a seam should not be more than 4.8 m wide and not more than 3 m high.

The roads used for travelling purpose should be separate from the haulage roads having rope haulage, belt conveyor, locomotive haulage or gravity haulage. The travelling road should be not less than 1.8 m high. Men are not permitted to travel on mine cars, tubs or conveyors.

The minimum sizes of pillars and the maximum width of galleries to be formed in a mine during development are prescribed by the Regulations. For the same depth the wider the gallery, the larger should be the pillar size. Similarly for the same gallery width, the size of a pillar increases with depth. The following table gives the pillar sizes as laid down under the Regulations.

Depth of seam from surface	maximum gallery width
	3m	3.6 m	4.2 m	4.8 m
	Minimum distance of pillar centres (m)
60 m	12.0	15.0	18.0	19.5
61-90 m	13.5	16.5	19.5	21.0
91-150 m	16.5	19.5	22.5	25.5
151-240 m	22.5	25.5	30.0	34.5
241-360 m	28.5	34.5	39.0	45.0
exceeding 360 m	39.0	42.0	45.0	48.0

Pillars should be of larger sizes near a fault plane which is generally a weaker section, near a crushed zone and in the area where the coal is son or friable. In hilly areas the pillar has to be large at local places under the hills as the depth from the surface naturally increases. Where the roof or floor has a tendency to creep or heave in the galleries, pillars should be large and the galleries small in width. If the pillars formed during development are expected to be depillared long after their formation, they should be of larger size. In steep seams the pillars are rectangular with the longer side along the strike. This provides the advantage of opening levels comparatively early.

The pattern on which the galleries are to be driven is decided by the manager and marked on the plan which is known as the projection plan. The direction in which the galleries are to be driven is therefore known to the surveyor and he has to mark the centre lines of the galleries on the roof in the coal seam and extend them upto the face daily or on alternate days depending upon advance of faces.