EIACP (PC-RP) on Environmental Problems of Mining

Chanda Colliery

Collapse of pillars in the 12 seam resulted in subsidence of the surface and a part of a coolie barrack, situated over the affected underground workings, sank into the cavity and was badly wrecked.

The 12 seam at this colliery was about 15 m thick and had a steep inclination of 1 in 1.8. The workings extended over an area of 75 m along dip and 180 m along the strike. The coal pillars were 9 m square and the galleries were 3.6 m wide. The height of the galleries varied from 3 m near the faces to as much as 12 m in the rise-side workings. The sandstone roof was consideredo be good. No fall of roof had occurred previously and props were used only occasionally.

The accident occurred at 3.30 a.m. when a large number of persons were asleep in the barrack. A surface area of about 44 m x 26 m subsided and the magnitude of subsidence varied from 0.3 m to as much as 20 m. The western portion of the barrack was wrecked and a large number of persons were engulfed in the debris. Rescue operations started at once and within one hour all the survivors had been extricated. One man actually rolled down the slope of the cavity into the mine workings, a fall of not less than 20 m, and on recovering his senses some hours later, walked out by the haulage incline. Ten persons got killed in the accident and six received serious injuries.

After the accident, the Inspector of Mines inspected the underground workings and except for two fractured pillars, found the remaining parts of the workings quite intact. An examination of the cavity on the surface showed that the east and west sides of it coincided with two fracture; planes, coated with mud which must have been carried down by percolating water.

With 9 m square pillars and 3.6 m wide galleries, the amount of coal left in the pillars was 51 % which, under normal circumstances, was adequate for the moderate depth of workings. However, the circumstances in this case were far from normal in following respects: –

1. The pillars were unusually tall
2. Inclination of the seam was very steep, and
3. Water was percolating through fracture planes which extend upto the surface.

Owing to the steep dip, the weight of the overlying strata would not act vertically and would tend to overturn the vertical pillars. The later support to the overburden had been weakened by the pronounced fracture planes which were lubricated by the muddy water percolating from the surface. Therefore the pillars failed to resist the movement of the overburden and got crushed.

Similar and more extensive collapses had taken place at two adjacent collieries in 1912 but warning symptoms had been noticed by the officials and precautions had been taken in time. In this case no one had gone to the affected area for at least 39 hours before the collapse and even if symptoms of imminent collapse were there, nobody was there to notice them.

Considering all these facts, nobody was held responsible for this accident.