40 years development and prospect of longwall top coal caving in China

Since introducing and innovatively developing the longwall top coal caving (LTCC) technology more than 40 years ago， China has achieved a great success and significant technology innovation， realizing once mining full height in thick coal seam with high production，high efficiency and low cost. The LTCC has become a main method of mining thick coal seam in China，which also becomes a symbolic technology in the coal mining industry of the whole world. In the development progress of the LTCC，the authors have successively tested high⁃opening caving，middle⁃o⁃ pening caving and low⁃opening caving，finally formed the low⁃opening caving technology in China. The hydraulic sup⁃ port structure has developed from the early four⁃column type to the current situation where four⁃column type and two⁃column type coexist today，and it is more advantageous for two⁃pillar support in intelligent panel. China’s LTCC technology development can be divided into two stages. In the stage of exploration，promotion and application in the first 20 years，according to the seam conditions in China，the technical advantages of the LTCC were fully exer⁃ ted，forming high production and efficiency mining model，soft roof⁃coal⁃floor thick seam mining model，hard roof⁃coal thick seam mining model and steeply inclined thick seam mining model，etc. In the stage of technological in⁃ novation and export in the recent 20 years，China has creatively developed the LTCC with large mining height in ex⁃ tra⁃thick seam and steeply inclined thick seam mining， and made breakthrough in intelligent mining and intelligent coal drawing technology，realizing the leap⁃forward development of the LTCC technology from introduction to output. China has formed a group of scientists that focus on the research of the LTCC，and whether the theoretical in⁃ vestigations or the technical achievements of the LTCC are well advanced in the world. The further research needs to focus on the comprehensive intelligent mining in the LTCC panels，the development of intelligent coal drawing technol⁃ ogy，the technology of improving top coal recovery in the end area. In addition，it should develop the water protec⁃ tion mining，green mining and disasters⁃reduction mining technology based on ground movement induced by mining， establish the unified field theory of overburden movement，and study the low⁃carbon technology path of the LTCC.