The 121 mining method of longwall mining first proposed in England has been widely used around the world. This method requires excavation of two mining roadways and reservation of one coal pillar to mine one working face. Due to considerable excavation of roadway, the mining roadway is generally destroyed during coal mining. The stress concentration in the coal pillar can cause large deformation of surrounding rocks, rockbursts and other disasters, and subsequently a large volume of coal pillar resources will be wasted. To improve the coal recovery rate and reduce excavation of the mining roadway, the 111 mining method of longwall mining was proposed in the former Soviet Union based on the 121 mining method. The 111 mining method requires excavation of one mining roadway and setting one filling body to replace the coal pillar while maintaining another mining roadway to mine one working face. However, because the stress transfer structure of roadway and working face roof has not changed, the problem of stress concentration in the surrounding rocks of roadway has not been well solved. To solve the above problems, the conventional concept utilizing high-strength support to resist the mining pressure for the 121 and 111 mining methods should be updated. The idea is to utilize mining pressure and expansion characteristics of the collapsed rock mass in the goaf to automatically form roadways, avoiding roadway excavation and waste of coal pillar. Based on the basic principles of mining rock mechanics, the equilibrium mining theory and the short cantilever beam mechanical model are proposed. Key technologies, such as roof directional presplitting technology, negative Poisson's ratio (NPR) high-prestress constant-resistance support technology, and gangue blocking support technology, are developed following the equilibrium mining theory. Accordingly, the 110 and N00 mining methods of an automatically formed roadway (AFR) by roof cutting and pressure releasing without pillars are proposed. The mining methods have been applied to a large number of coal mines with different overburdens, coal seam thicknesses, roof types and gases in China, realizing the integrated mode of coal mining and roadway retaining. On this basis, in view of the complex geological conditions and intelligent mining demand of coal mines, an intelligent and unmanned development direction of the equilibrium mining method is prospected.
Dr. Manchao He is an expert in Mine Engineering and Rock Mechanics. He is an Academician in Chinese Academy of Sciences, professor at China University of Mining and Technology at Beijing (CUMTB), and the vice president at International Society for Rock Mechanics and Rock Engineering (ISRM) of the term 20152019. He is the director of the State Key Laboratory for Geomechanics and Deep Underground Engineering, the chairman of China National Group of ISRM, the president of Chinese Society for Rock Mechanics and Engineering (CSRME), and the chairman of the Soft Rock Engineering and Deep Disaster Control Sub-society of CSRME. He is also Chief Scientist of the Major Program of the National Natural Science Foundation of China, Chief Scientist of 973 Program and winner of National Outstanding Youth Scholar Fund. He has published 4 books and over 190 research papers. He also serves on the editorial board member of several journals, including Journal of Rock Mechanics and Geotechnical Engineering.
Dr. Qi Wang is professor of China University of Mining and Technology at Beijing (CUMT) and Shandong University. His research focuses on coal mining methods without pillars and the surrounding rock support theory. He is the executive dean of Research Institute for Deep Underground Science and Engineering of Beijing, the director of the Shandong Province Engineering Laboratory of Safety Control for Underground Space. He is also the vice-president at International Society for Rock Mechanics and Rock Engineering (ISRM) Soft Rock Commission, the vice-chairman of Soft Rock Engineering and Deep Disaster Control Sub-society of Chinese Society for Rock Mechanics and Engineering (CSRME). He won the Youth Yangtze River Scholar and the outstanding mid-aged experts in Shandong Province. He took charge of 4 National Natural Science Foundation of China (NSFC) and 21 projects from enterprises and institutions. Up to now, he has published 75 SCI- or EI-indexed papers as the first or corresponding author and hold 36 Chinese invention patents as the first inventor.