Research on the abutment stress evolution of working face mining under triangular oblique coal pillar in shallow buried close coal seams

Aiming at the influence of the overlying coal pillar of working face in shallow coal seam, there are problems such as strong ground pressure and large deformation of the roadway caused by stress concentration of the section coal pillar. Taking the 31109 working face of Cuncaota No.2 coal mine as the research background, the combined method of field measurement, numerical calculation and theoretical analysis was adopted. The evolution law of the size and range of superimposed stress through the triangular coal pillar under two mining stages were mastered, the changing of coal pillar pressure in the two mining stages and the damage mechanism of adjacent roadways were revealed, the scope of roadway enhanced support and the scope and timing of key support were clarified. The research results show that: the overlying triangular diagonal coal pillars cause stress concentration on the working face of lower coal seam, and the maximum position is located under the diagonal coal pillar. After the 31206 working face in lower coal seam was mined, the stress of the coal pillar in the 31109 working face increased to the maximum stress, the stress peak area was located near the overlapping area of the coal pillar in the overlying diagonal section, the width of the peak area was 240 m, the deformation and damage of the roadway in this area was more obvious. During the mining process of the 31109 working face, there were stress peak areas in the overlapping area of the coal wall, the coal pillar and the overlying oblique coal pillar, they form stress double peaks. As the working face advanced, the stress of the double peaks continuously increased. Moreover, the stress peak area of the coal wall gradually shifted towards the direction of the section coal pillar. When the working face reached the section coal pillar overlay area, the double peaks merge into a higher single peak stress. The section coal pillar stress reaches the maximum when the working face emerges from the oblique coal pillar, and the stress decreases rapidly after exiting the coal pillar overlay area. In general, the maximum stress in the stress peak area of the section coal pillar after mining in the 31109 working face increased by 56%, and the range of the peak area expanded by 50% . The mechanism of increasing stress in section coal pillar is that with the working face advances, the size of the overlying triangular diagonal coal pillars continuously decreased, and the degree of stress concentration continuously increases. When the working face advances to the end area of the triangular coal pillar, there is an overlap and mutual interaction between the stress in the oblique intersecting coal pillars, the advance support pressure of the working face, and the stress in the segmental coal pillars. This interaction results in the formation of a stress peak zone in the section coal pillar. When the the working face out the boundary of coal pillar (triangular coal pillar apex), it creates a stress concentration zone, leading to deformation of the segmental coal pillars and damage to the roadway in that area. Based on this observation, it is proposed to carry out anchor cable and grouting reinforcement support for the stress peak area and core area of roadway before mining in the 31109 working face. On-site industrial test achieved good results, ensuring the safe mining of the 31109 working face passing through the triangular oblique coal pillar area. © 2024 China University of Mining and Technology. All rights reserved.