Mining Thick Seams

Longwall retreating is one of the primary methods of mining in many coal mining areas. There is a high degree of mechanization, and mine safety is receiving an increasing amount of emphasis.

Thick seam coal mining is important in Russia. Many high-qual­ity coal seams exceed 35 metres (12 feet) in thickness — the normally accepted classification for a thick seam (although this var­ies in different countries). Some of these thick seams are of key im­portance in major mining basins. Seam thickness is the most signifi­cant factor which is taken into account in mining practice. The increasing strata movement with increasing seam thickness requires not only specialized extraction techniques, but also highly specialized ground control and support methods. This is certainly true of the coal basins where coal seams are gassy and the majority of coal is liable to spontaneous combustion. Coal seams occur at a depth of between 350 and 710 metres (1,150 and 2,330 feet).

Longwall retreating is the primary method of mining at the col­lieries with more than 98 per cent of the total output. Application of a mining method with the coal face being advanced down the dip is steadily expanding; shortwall pillar extraction with power loaders is being successfully employed.

Coal faces and development headings are equipped with instru­ments for automatic gas protection and centralized telemonitoring of methane content. Data on gas conditions in development headings which are particularly dangerous from the viewpoint of methane content, and in all coal faces are transmitted to the mine dispatcher's control panel. In order to reduce gas content in mine workings, extensive use is made of preliminary gas drainage of the coal seams, gas drainage of roofs to be caved and also of the goaf.

The main trend in mine transport is towards high-capacity au­tomatic conveyer systems. In underground workings transport of men and materials is by high-capacity electric locomotives; in in­cline roadways, by ropeways, floor-mounted haulage and up-to-date hoisting installations.

The mining district is usually developed by mine shafts. The mining method is longwall retreating along the strike and down the dip. The mining area is divided into two blocks east and west. In the eastern block, the panels are mined down the dip, in the western block, mining takes place along the strike. The faces are 200 metres long and operate along the strike of the seam. Sandstone forms the immediate roof and floor of the seam. Each face is mining a 3.5-metre thick section of coal, and a 0.5 to 0.8 metre thick pillar (band) of coal is left between two panels to form the roof of the lower face.

Each face is equipped with a double-ended dram shearer. The drams are 1.8 metres in diameter and a 0.6-metre web of coal. The leading dram cuts the top section of the face, and the trailing dram cuts the bottom section. Water jets are fitted to the drams for dust suppression. Coal passes along the face on the armoured face conveyer to the crasher installed at the main gate end of the conveyer, which reduces the size of the coal before it is delivered to a beam stage loader in the main gate.

The faces are operated on two production shifts and one main­tenance shift per day.

Each face is supported by shield supports.

It should be stressed that special attention is paid to under­ground methane drainage. The methane is pumped through pipes first to the tail gate and then through the mine gate to the upcast shafts and then to the surface, where it is used for heating. Two sensors for continuously monitoring the emission of CH₄ are situ­ated in the top panel, one in the main gate, and the other in the tail gate. These are placed 20 metres in front of the face. The con­trol room at the mine's surface automatically monitors and records CH₄ emissions throughout the mine.

In coal face and development operations, use is made of cur­rent forecasting of the liability to sudden outbursts, that is estab­lishing dangerous and non-dangerous zones.

All coal faces are equipped with mechanized complexes, com­prising power loaders. In underground haulage roadways, use is made of high-capacity belt and apron conveyers. Coal is hoisted to the surface through two skip shafts. Monorails are widely used on levels for transport of materials and equipment to coal faces and development headings. Some of production processes are auto­matic.

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