Room and pillar mining

The percentage of coal recovered from a mineable seam depends on several factors, such as the number and size of protective pillars of coal thought necessary to support the roof safely, and of the percentage of pillar recovery. In general, the less coal that is extracted the less is the need for costly roof supports. The necessity to protect valuable surface land also has a bearing on the amount of coal mined. In some areas where the surface land is owned by the coal producer, most of the available coal can be mined, whereas in other areas a lesser percentage of the coal is mined to prevent surface damage from subsidence. 

On the other hand, in certain heavily industrialized areas, such as Great Britain and Western Europe, the need to mine every possible ton of coal may override consideration for the surface. In such cases, and every care is taken to minimize damage to the surface, total extraction inevitably gives rise to some surface subsidence. 

The percentage of coal that is removed may also be determined by the need to protect the mine workings from overhead water. For example, when mining operations are carried out below the sea (such as, as has already been mentioned, in the North Sea off the coast from Sunderland in North East England), only narrow working places may be allowed with large protective pillars of coal being left permanently between the rooms. 

---

A room-and-pillar mining system. Pillars are left behind in the rooms to support the roof. 

Two general systems are used in underground mines room-and-pillar mining and longwall mining. 

Gennaro, G.M. William, G. 1986. Mine subsidencce damage from room and pillar mining in Illinois [J]. International Journal of Mining and Geological Engineering 4(2). 

Once a coal deposit has been reached by a shaft, slope, or drift mine, woikers mine the coal by one of two methods the room and pillar method or the longwall method. Room and pillar mines extract coal at greater depths and are usually left standing when the mine is abandoned. Longwall mines are used at shallower depths and are allowed to collapse as the mine progresses. 

Some mention should also be made here of a technique known as room and pillar mining (Figure 5.11) which has been employed for many years in North America as a means of developing a coal face and, at the same time, retaining supports for the roof. As the name implies, the room and pillar method uses rows of large pillars of coal to support the roof of a mine. 

Room-and-pillar mining A mining method in which a designated area is divided into regnlar-shaped coal pillars through the paraUel development of entries and crosscuts. After the area is so developed, the ranaining piUars are mined by slicing them into smaUer pillars. 

Zipf, R.K., and C. Mark. 1997. Design methods to control violent pillar failures in room-and-pillar mines. Transactions of the Institution of Mining and Metallurgy 106 (September-December) A124-A132. 

In room-and-pillar mining, the retreat or pillaring phase occurs when miners remove coal blocks originally used for support as the working section withdraws. The method requires stringent ventilation and roof control safeguards (p. 7). 

---