Research on Control Technology of Initial Mining and Roof Cutting Pressure Relief in Short Wall Working Faces of Extra Thick Coal Seams

Aiming at the difficult engineering problem that a large area of suspended roof is prone to form and lead to significant accumulation of elastic energy when short wall working faces of extra thick coal seams are mined under the hard roof condition, taking the 26115 working face of Nanyangpo Coal Industry as the engineering background, the research is carried out on the control technology of initial mining and roof cutting pressure relief. By analyzing the dynamic evolution laws of roof subsidence displacement, coal wall and coal pillar stress in the advancing process of working faces, the disaster causing mechanism of large area suspended roof is revealed. The research results show that without taking presplitting measures, as the working face advanced to 150 m, there only occurs elastic bending and subsidence on the roof, with a maximum subsidence displacement of 2.96 m, a large area of suspended roof is formed above the goaf, and there is no roof break or collapse happened, a large amount of elastic energy is accumulated and a risk of strong dynamic disasters is existed. After adopting deep hole blasting and presplitting roof cutting, the roof integrity is actively weakened, the initial weighting step distance of the working face is shortened to about 60 m, the roof is timely fractured in an orderly manner and completely collapsed, and is in a plastic deformation stage. After the collapsed gangue filled the goaf, the final subsidence displacement of the roof is stabilized at 9.3 m. At the same time, the deformation of the roadway surrounding rock is significantly reduced after roof cutting, indicating that this technology can significantly control the mutation collapse of the roof, providing a theoretical basis and technical reference for safe and efficient stoping of working faces under similar conditions.