Longwall mining method

Figure 1. Schematics of the top coal caving longwall mining method.

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. 

Thus, the method offers the advantages of coal recovery near that attainable with the conventional or continuous systems. In addition, longwall mining offers efficient method of coal recovery under extremely deep cover or overburden or when the roof is weak. Furthermore,... 

Longwall mining A mining method in which a large rectangular section of coal is removed in one continnous operation. Equipment is installed along one side of the section (the longwall face), and the coal is removed in slices 2-4 ft thick. The excavated area behind the eqnip-ment is allowed to cave. 

Longwall mining uses a machine that is pulled back and forth across the face of the coal seam in larger rooms. It is not a major mining method in the United States at this time. Coal recovery using this method is greater than in room-and-piliar mining and... 

A modification of this method, using a continuous mining machine on faces up to 150 ft long, is known as shortwall mining. It uses the roof support system of self-advancing chocks developed for longwall operations. 

Room and pillar techniques are used to extract most of die trona. Conventional blasting methods as well as drum (ripper) and borer mining machines are employed. Longwall and shortwall mining techniques which involve hydraulically supporting the overburden wliile undercutting the trona seam have recently been introduced. In these methods, die hydraulic supports are advanced after the trona is extracted. Eventually the previous cut caves in. These newer techniques allow over 70% recovery of die ore compared to 50% recovery for conventional room and pillar methods. 

In this paper, the shearer machine of Parvadeh coal mine in the central Iran was selected for case study and data collection. The extracted coal seam of this mine has 1.8 m thicknesses and is mined by retreat longwall method using a double-drum shearer (Fig. 1). 

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