Research on roof stability and precise control technology throughout entire life cycle of open-off cut

To address the lack of systematic and in-depth research on roof stability and its control throughout the entire life cycle of the open-off cut from roadway excavation to the first caving of the main roof, the concept of the entire life cycle of the open-off cut was proposed. The entire life cycle of the open-off cut was divided into five stages: primary roadway excavation, secondary roadway expansion, coal mining equipment installation, immediate roof caving in the goaf, and first caving of the main roof in the goaf. Through theoretical analysis, it was concluded that geological conditions were the fundamental factor determining roof stability in the open-off cut. Roadway layout, roadway span, and excavation disturbance were important mining technical factors affecting the stability of the roof strata. Support technology was the key measure for controlling roof stability. By establishing a mechanical model of the main roof rock beam, the overlying strata structure characteristics of the open-off cut in the five stages were studied, and the spatiotemporal evolution and dynamic change process of the open-off cut roof from bending subsidence to collapse were revealed. Corresponding control technologies were proposed according to the roof structure characteristics at different stages. During the roadway excavation stage, active support with bolt-mesh-cable should be adopted. Before initial mining, roof cutting and pressure relief should be conducted behind the hydraulic supports. Industrial trial results showed that implementing blasting pre-splitting for roof cutting behind the supports could pre-damage the integrity of the open-off cut roof, reduce the first caving interval of the goaf roof, weaken the first weighting intensity of the main roof, and avoid the safety hazard of large-area roof hanging in the goaf.