EIACP (PC-RP) on Environmental Problems of Mining

Kawadi Open cast Coal Mine

The present area of Kawadi opencast mine was earlier part of the underground New Majri Mine No.3 which was started in the year 1938. Majri seam, 15 to 19 m thick and dipping at 1 in 4.5, had been opened up through inclines and extensively developed on the bord & pillar system in two sections. The property has a major fault with a throw varying from 14 m to 32 m. Two opencast mines were started in the property to extract the developed Majri seam with the barrier between the two mines being along this fault plane. Kawadi mine, started in July 1991, was on the dip side of the fault, whereas the property lying on the rise side of the fault was allocated to New Majri opencast mine. The overburden had black cotton soil at the top, 7 m to 28 m in thickness, below which were fractured sandstones varying in thickness from about 13 m to 40 m. The coal seam had a high moisture content of 6.5% and was very susceptible to spontaneous combustion. Spontaneous heating in the exposed coal galleries had started at the beginning of 1998 and had extended on all sides. The usual practice at the mine was to expose the developed coal pillars by removing the overburden, extract the pillars and then cover up the extracted area by dumping the overburden material to control heating.

While granting permission to extract the seam by open cast method using HEMM, DGMS had imposed the following conditions regarding formation of benches:

1. The height of benches in black cotton soil shall not exceed 5 m and no work shall be done within a distance of 10m from the toe of such benches.
2. The height of benches in other overburden strata shall not exceed 10 m.
3. The width of benches shall not be less than 10m.
4. Width of the first coal bench below the last overburden bench shall not be less than 10m and the height of any coal bench shall not exceed 5 m.
5. Special care shall be taken where any slip or weakness plane or any other geological disturbance exists so as to prevent danger to work persons.

During inspection of the mine on 19.3.1999, the inspector had noticed serious contravention of these conditions. Height of benches in loose strata consisting of black cotton soil and alluvium was as much as 35 m with undercutting upto 2 m depth. An improvement notice under section 22 A (1) of the Mines Act was issued. Compliance with the conditions could be effected only in December, 1999.

The accident:

The accident occurred on 24.6.2000 in the second shift when 13 workers, under the supervision of an overman and two mining sirdars, were engaged at the floor of the coal bench in various activities like drilling, unloading of explosives from the explosive van, working the hydraulic excavator, etc. At about 3.50 p.m., one of the workers noticed loose debris falling from the top of the benches on the rise (barrier) side. By the time he could raise an alarm, loose debris and boulders started sliding down rapidly into the quarry. 5 persons tried to run away while 10 others took shelter behind the HEMM and the explosive van. One person had left the area earlier.

The total volume of material that slid down was more than 20,000 m3. All the 10 persons who had taken shelter behind the HEMM and explosive van were completely buried under the debris. The 5 persons who had tried to run away were partially trapped but could escape with minor injuries.

Machines were deployed immediately for removal of the debris. All the 10 dead bodies could be recovered by 5 a.m. on 25.6.2000. About 1000 m3 of material had to be removed to take out the bodies.

Observations:

1. Height of benches in the black cotton soil was as much as 12 m with width of only 3 m to 8 m.The next two benches in sandstones were 12 m to 15 m high and had widths of less than 5 m.

    

   The coal bench was 15 m to 18 m high and was almost flush with the sandstone bench above, the combined height at places being as much as 52 m.

2. The strata had sets of geological discontinuities, parallel as well as at an angle to the fault plane.
3. Heavy rainfall had occurred in the area on 6th, 10th, 11th and 17th June prior to the accident.
4. Active fire was noticed in the exposed underground galleries as well as in the pillars on all sides.
5. An earthquake measuring 4.0 on the Richter scale was reported to have occurred in the area on 22.6.2000 at about 4 p.m. The epicenter of the tremor was probably 35 km west of Kawadi mine.
6. From the disposition of the collapsed material at the accident site, it appeared that the slide had started from the bottom of the quarry and extended to the fault plane in the barrier.

Conclusion:

The benches failed because of their excessive height and very small width. The following factors might have contributed to the instability of the benches:

1. Sets of geological discontinuities in the strata
2. The fault plane along the barrier between Kawadi and New Majri mines.
3. Presence of water in the strata due to heavy rainfall prior to the accident.
4. Failure of pillars on fire in the belowground workings under the benches.

The management was held responsible for the accident as it failed to maintain proper benches as per the conditions stipulated in the permission letter.