**2.2 Longwall top coal caving**

The longwall top coal caving (LTCC) method was first developed in the 1950s and 1960s in the former Soviet Union and France to increase coal resource extraction and

**Figure 3.** *Schematic diagram of longwall mining.*

improve productivity. During the 1970s, it was also adopted in Yugoslavia, Hungary, Romania, and former Czechoslovakia (now the Czech Republic) but generally did not receive much success at the time. The technology was formally introduced in China under extensive research and development. It has become progressively popular in China and rapidly became a significant means of extracting thick coal seams with great success in productivity, cost, and safety [23].

A thick seam is commonly considered to be one that cannot be mined underground safely and economically in single-pass cutting using the current technology, even though the exact thickness defined varies in different countries. Underground thick seam mining technologies have been developed and practiced worldwide for decades. Some methods used for extracting thick seams, including hydraulic mining and room and pillar methods, are less popular.

The multi-slice longwall mining practiced mainly in China is gradually being replaced by the LTCC method because of its lower development and operating costs, given thick seams have favorable caveability. The high-reach single-pass longwall used in Australia has been successful, but the cutting height is limited to less than 4.8 m with current equipment. To increase the recovery of Australian thick seam reserves, the LTCC mining technology is providing an alternative solution to economic underground thick seam mining in Australia [24–27]. The conceptual model of longwall top coal caving (LTCC) is shown in **Figure 4***.*
