Mechanical principle and mining methods of automagical entry formation without coal pillars

Coal is the principal energy of China, and the coal industry is an important basic industry related to the energy security. For a long time, the underground coal resources mining in China has always been based on the longwall 121 mining method. This mining system has many problems such as waste of coal resources, high rate of entry excavation and concentrated stress of coal pillars. In order to solve the three bottlenecks and prominent problems of “safety, mining cost and coal recovery rate” existing in the current mining system, we established a mining engineering model based on the mining damage invariant equation, analyzed the mechanical principle of automagical entry formation without coal pillars. On this basis, the key technologies of 110 and N00 mining method, such as directional presplitting and pressure relief of roof, NPR bolt/cable support are developed. The technical objective of “being able to control the roof, cut off the roof, make the roof easy to collapse and protect the entry rib” has been achieved. The 110 mining method of automagical entry formation without coal pillars and the N00 mining method at different development stages have been formed. The 110 mining method unifies the two sets of processes of coal mining and excavation initially, so that each coal mining face can dig one less mining entry, and no pillar mining is realized. The N00 mining method is based on the 110 mining method, which completely unifies the two processes of coal mining and excavation. The mining pressure is used to automatically form the roadway, thus eliminating the excavation of roadways and thoroughly eliminating the long-standing problem of strained relations of mining and excavation. The field practice shows that the 110 mining method cuts off the stress transmission between the roof of the goaf and the roof of the entry. The mine pressure and self balance of the surrounding rock of the retained entry is realized by using the crushing and swelling property of the collapsed gangue. The N00 mining method innovates the original mining technology, changes the layout of the traditional mining system, and realizes no entry digging and automatic entry formation in the whole mining area.