Longwall mining

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 systems allow a 60%-100% coal recovery rate when surrounding geology allows their use. Once the coal is ranoved, usually 15% of the section, the roof is allowed to collapse in a safe manner (WCA, 2009). 

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Booth, C. J. 2002. The effects of longwall mining on overlying aquifers. In Younger, P. L. Robins, N. S. (eds) Mine Water Hydrogeology and Geochemistry. Geological Society, London, Special Publications, 198, 17-45. 

There are about 100 longwall mining installations in U S. underground mines, most of which are located in Appalachia and the Midwest. The applicability of the methodology to a specific coalbed depends upon several factors, including the thickness and suitability of the seam and the strength of the surrounding strata. See Fig. 12. 

Fig. 12. Example of longwall mining. (National Coal Association)...

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

Kizil, G.V. A.M. Donoghue (2002). Coal dust exposures in the longwall mines of New South Wales, Australia a respiratory risk assessment. Society of Occupation Medicine 52 (3) 138-149. 

Study on stability of thick-hard key stratum based on numerical simulation in longwall mining... 

When the longwall mining face was advanced at the distance 410 m from open-off cut, the hard-... 

The top coal caving longwall mining is widely used in China, and the coal seams to which it has been applied are getting thicker and thicker. However, as the coal seam becomes thicker, the top coal will not be fully broken and fall onto the rear AFC, rather it falls into the gob. In order to solve this problem, the first step is to understand how the front abutment pressure is distributed and how the top coal is fractured in the mining process. 

Using both field measurement and theoretical analysis, this paper aims to study the nature of abutment pressure distribution and failure and migration process of the top coal in extra-thick coal seam top coal caving longwall mining. 

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. 

The longwall mining system, used for many years in Europe, involves the use of a mechanical self-advancing roof in which large blocks of coal are completely extracted in a continuous operation (Figure 5.10). Hydraulic or self-advancing jacks chocks) support the roof at the immediate face as the coal is removed as the face advances, the strata are allowed to collapse behind the support units. 

The shortwall mining system originated in Australia and is, in essence, a combination of the continuous mining and longwall mining concepts. 

In fact, eqnipment costs may also be reduced by employing the development equipment during the retreat from the face. However, it should be noted that the passes along the coal face are restricted to one direction only (cf. the longwall mining system) since the mining machine is not nsnally adaptable for cutting in both directions. 

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. 

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