Longwall mining has a long history of successful applications, even in thin and inclined coal seams [2]. This type of mining is more mechanized than any other method, and necessitates careful attention to the selection of the expensive equipment required. Longwall mining is a unique method with one principal variation. According to the direction of coal extraction, there are longwall advance mining [3] and longwall retreat mining [4].

6-1 Longwall Advance Mining

Longwall advance mining has been primarily used in the deeper underground mines where strata pressures [5] do not permit maintaining roadway [6] for long period of time.

The majority of coalfields in Europe use longwall advance system of mining. The coal seam is divided into panels [7], generally 100 to 230m wide by up to 1800m long. Production may commence following a minimal capital outlay [8] for pre-production development. Yet the geological conditions [9] ahead of the advancing coalface may be uncertain, thus introducing an element of risk. Any sudden worsening of geological conditions may cause the production face to halt and an equipment capital outlay can be temporarily at a stand still. Shallow mining depths are not favored longwall advance mining; however, weak strata may require its use even though it may not suit North American requirements for high productivity.

A. Advance system with single entry [10]: The single entry is driven only a short distance ahead of the advancing face to avoid excessive frontal abutment pressures [11], The advance of roadways has been greatly improved through the use of longwall shearer [12] for roadway excavation.

The main problem of the longwall advance system with single entry is maintaining the roadway behind face in the gob [13] for the life of the panel. Roadway support is provided by arches set [14]. The packs [15] are built along the gob edge for maintaining the roadway. The application of the Pump Pack [16] for pack building has reduced the difficulties relating to roadway maintenance [17].

B. Advance system with double entries [18]: These have rib pillars [19] with a least width equal to or greater than one tenth of the panel depth separating panels. The ribs provide roadway protection against strata pressure deformation [20] effect. The driving of double entries in advance is integrated with the transport of coal from the longwall face. The main advantage of this system is that there is no need for roadway maintenance because one collapse is with the gob and the other in the rib is not affected by gob closure [21].

The mining system requires more development work, but this is more than offset [22] by the savings in roadway maintenance.

6-2. Longwall Retreat Mining

Longwall retreat mining is basically the same as longwall advancing extraction, except that the coal seam is block-out [23] and then retreated in panels between development roadways. Its advantages ov

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