Shrinkage stope mining
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Shrinkage stope is a generic term used in mining to describe the process of mining upwards from a lower to a high horizon, leaving broken rock in the excavation created. The broken rock acts as a working platform, and helps to stabilise the excavation by supporting the walls.
The technique can be used for ore mining in shrinkage stopes, for raising, and for underground construction projects where excavations of considerable vertical height may be required, such as ore and waste bins, crusher rooms, penstocks and tailrace tunnels.
Because blasted rock takes up more volume than rock in situe, some of the broken material must be removed on a periodic basis, to maintain the required relationship between the back (or roof) of the excavation, and the level of the broken material in the excavation. This is achieved by drawing the blasted material through drawpoints on the lower level, which are constructed before shrinkage begins. Access to the space between the broken material and the back of the excavation must be mainained for access of men and materials, and for ventilation. Such access is usually provided by previously installed raises, usually equipped with ladderways.
When properly planned and executed, shrinkage mining is a very effective technique for ore mining and underground construction. It is used where the hanging and footwalls of the excavation are strong enough to be self supporting, although artificial support such as rock and cable bolts may be installed as shrinkage progresses. Where the technique is used for ore mining, careful planning and scheduling are required to ensure consistancy of ore grade and production tonnage.
