The First Application of N00 Mining Method in the World

a Key Laboratory for Geo-mechanics and Deep Underground Engineering, China University of Mining & Technology, Beijing 100083, China
1. Historical evolution of mining methods
1.1 The traditional mining method
The traditional 121 mining method of longwall mining originated in England, which is widely used around the world. The method requires the excavation of two mining roadways and the reservation of one coal pillar to mine one working face. The degree of roadway excavation is considerable, and the mining roadway is destroyed along with coal mining. The stress concentration at the coal pillar is prone to causing large deformations of the surrounding rock, rock bursts and other disasters, and a large volume of coal pillar resources are wasted. Meanwhile, the fracture and collapse patterns of the overlying strata between the goaf and coal pillar are different, easily leading to uneven ground surface subsidence and environmental damage. A schematic diagram of the 121 mining method is shown in Fig. 1. 1.2 The new mining method 
To solve the above problems, Prof. Hemanchao, academician of Chinese Academy of Sciences, changes the traditional concept of utilizing high strength support to resist the mining pressure for the 121 mining methods. The scientific idea is innovatively proposed, which utilizes the mining pressure and broken expansion characteristics of the collapsed rock mass in the goaf to automatically form roadways (AFR), eliminating roadway excavation and coal pillar reserve.
The new N00 mining method of the AFR with non-pillars eliminates the roadway excavation for the working face and realize the integrated mode of coal mining and roadway retaining, as shown in Fig. 2. The mining technique, equipment system, layout of the working face and roadway are changed under the N00 mining method (He & Wang). The roadway is automatically formed and retained by roof cutting on one side of the working face, and the roadway excavation (except the boundary roadway) and coal pillar reserved in the panel are eliminated.
The mining methods are applied to a large number of coal mines of different burial depths, coal seam thicknesses, roof types and gas content, successfully 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, the intelligent and unmanned development direction of the equilibrium mining method is prospected.
2 Typical application of the N00 mining method
The N00 mining method of the AFR with non-pillars has been successfully applied in the Ningtiaota coal mine, a shallow mine in western China, which is the first application in the world. The geographic location and roadway layout of the coal mine are shown in Fig. 3. Combined with the field application effect of the N00 mining method in the stages of roadway formation and reuse, it can be seen that the integrated mining mode of coal mining and roadway retaining is formed, which realizes roadway automatic forming and coal mining with non-pillars. This mining method effectively controls roadway surrounding rocks, meeting the engineering requirements, as shown in Fig. 4. The successful application of the N00 mining method verifies the correctness of "equilibrium mining" theory of the "utilization of two aspects and elimination of two aspects" with an integrated mode of coal mining and roadway retaining. The mining mode and technique of no coal pillar reserved and no roadway excavation are formed to ensure the safe and efficient mining of the working face, laying the foundations for intelligent and unmanned mining.