EIACP (PC-RP) on Environmental Problems of Mining

Dhemo Main Colliery

This accident occurred in the Dishergarh seam which was 3.6 to 4.8 m thick and was inclined at 1 in 5.5. The seam was worked through two shafts which were 350 and 360 m deep.

Extraction of pillars was started in 1935 in the extreme dip workings which were at a depth of about 600 m from the surface and by January, 1941 an area of about 600 m x 150 m had been extracted without any stowing of the goaf. However, in order to prevent accumulation of inflammable gas in the goaf and to prevent spontaneous combustion of the coal left in the goaf, water was allowed to accumulate in the goaf almost upto the working places. For this purpose, the line of extraction was maintained on a level line. No undue difficulties had been experienced upto January, 1941 but thereafter, as the width of the extracted area exceeded 150m, the load on the rise-side pillars became excessive and bumps started occurring. To overcome this problem, a narrow barrier of coal was left across the rise side of this goaf in the hope that this barrier would be able to carry the abutment load and the old goaf would be isolated. As pillar extraction was started on the rise-side of this barrier, the barrier proved ineffective and pillars began to fail under excessive abutment load. As each pillar or line of pillars in turn failed, the load was transferred to the next line. In May 1941, because of heavy bumps, loss of coal and incipient heating, the district below the 23rd level had to be isolated and filled with water. It appeared that further extraction could not be done without resorting to stowing. A stowing plant was installed and brought into operation in 1943. Many of the galleries below the 21st level were stowed with the object of arresting the movement. In 1945, attempt was made to re-start extraction of pillars with solid sand-stowing of the goaves, but bumps followed the extraction of every pillar and frequently after extraction of only a part of a pillar. This indicated that the old goaves had not subsided upto the surface and that there was little or no relief of load on the abutment which continued to fail and advance.

It was evident that despite the adoption of stowing for pillar extraction since 1945 and the strengthening of pillars by advance stowing of some galleries and partial stowing of others, it had not been possible to control the forces unleashed by the extraction of large areas without stowing prior to 1943. Attempts to extract pillars lying between No.16 level and 25 level were made on several occasions but extraction could not be done over any large area.

On 10.7.1952 when work persons were engaged to make a roadway through the sand-packed area to reach a pillar in No.17 level with a view to extracting it, a bump occurred dislodging coal on No.1 east main dip haulage road between No.14 level and 17 level but fortunately no one was injured. The work in this area was kept suspended for several shifts till the movement in the strata ceased. On 12.7.1952 men were engaged to clean up the fallen coal in the haulage road and this work was in progress when a bump occurred and roof rock, about 40 cm thick, collapsed at the junction of No.15 level over an area measuring about 21 m x 6.7 m. Six cogs and numerous props were dislodged and 12 miner-loaders were buried, 10 of them were killed instantly and the remaining 2 succumbed to their injuries a few hours later.

As the accident had resulted from a “bump” over which the manager had no control, it was classified as a case of misadventure. The Inspector prohibited further extraction of coal from the district until the galleries in a large area of workings to the rise side of No.25 level had been stowed with sand so that the pillars would be stabilized, and the density of support had been increased.

This accident lent support to the view held by many mining engineers that the bord & pillar method was not a suitable method for working thick seams at depths exceeding 300 m. Satisfactory results had been reported from mines where the longwall method in conjunction with sand stowing had been adopted for extraction of thick seams in virgin areas in deep mines.