Impact mechanism of clamped coal pillar in sublevel fully mechanized top coal caving in the near vertical extra thick coal seam

Based on the horizontal sublevel caving mining of the near vertical extra thick coal seam in Yaojie No. 3 coal mine, the mechanical model of “clamped rock beam” in dip section and “U-λ” rock plate in strike section were established in this paper. The mechanism of the rock burst of the coal pillar clamped by the roof and floor in the horizontal sublevel mining of the near vertical coal seam was revealed. The stress distribution and the evolution law of plastic zone were analyzed. Furthermore, qualitative monitoring and space-time quantitative monitoring of microseisms in the working face were carried out. The research showed that, when the “cantilever” structure formed by the roof slate layer reached a certain length limit, the “U-λ” rock plate was fractured that produced impact load on the coal body below, resulting in strong ground pressure behavior. The horizontal stress on the coal pillar increased with the continuous mining of the working face to the deep. The elastic deformation energy accumulated in the coal body was released that made the coal body below the working face form a certain depth of shear compression tension fracture zone damage area. The lower part of the working face was a huge thick bottom coal, that accumulated a large amount of elastic strain energy. It produced plastic deformation and released its elastic property, resulting in sudden floor heave of the bottom plate and the increase of the support resistance. With the advance of the working face, the top coal and the loose broken coal and rock mass above it collapsed. As a result, the rock block released a lot of energy in the process of sliding and rotating instability, causing dynamic load disturbance to the working face. © 2023 China University of Mining and Technology. All rights reserved.