When mineral is extracted from an underground mine the void or goaf is packed with sand or other packing material wherever it is conveniently and cheaply available in sufficient quantities. The process is known as "goaf stowing" or "goaf packing" and often simply as "stowing". The material employed for goaf packing may be stone or shale obtained from bands of stone or shale if they are present in the coal seam under extraction. They may be used for erecting pack walls or for stowing in the goaf, in the crushed form. Other material which is sent down the mine for goaf stowing may be sand, earth, boiler ash, crushed material available from quarry overburden, shale pickings at the screening plant, washery refuse, mill tailings, or slag from blast furnace for iron ore smelting.
The material should be free from carbonaceous matter.
The packing material may be packed at site by —
1) Dumping it with baskets with the help of human labour as in hand packing.
2) Transporting the material with water in pipes and allowing the water to percolate through bamboo matting or similar perforated barricade erected at site. This process is known as hydraulic stowing.
3) Throwing it with the help of a high speed belt conveyor as in mechanical stowing.
4) Introducing the material in a stream of compressed air as in pneumatic stowing.
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