Study on the Evolution of Concentrated Stress Distribution in Close-Proximity Coal Seam Residual Pillars

Abstract

Closely spaced coal seams are extensively distributed across China. As shallow coal resources face increasing depletion, coal mining is gradually extending to deeper zones. Deciphering the stress distribution pattern of the residual coal pillar floor in closely spaced coal seams is of profound importance to the safe and efficient mining operations of lower coal seams while also offering certain theoretical guidance for the development of deep closely spaced coal seams. Taking the 22,206 coal working face of Daliuta Huojitu Well as the research background, this study adopted a combination of theoretical analysis and similar simulation experimental methods. Systematic analysis was conducted using multiple monitoring technologies, including distributed optical fiber sensing (DOFS), digital image correlation (DIC), and pressure sensors, to explore the evolutionary characteristics of stress distribution in the floor of residual coal pillars in closely spaced coal seams. The research results show that the depth of influence of upper residual coal pillars and goafs on the mining of lower coal seams differs. When the upper section is a goaf, the minimum safe distance is 20.4 m; when the upper structure is a residual coal pillar, the minimum safe distance is 39.9 m. The stress concentration coefficient under residual coal pillars is higher than that in goaf regions. With the advancement of the working face, the stress influence angle gradually decreases from ~80°46^′ to 46°22^′, while the peak stress concentration coefficient rises from 1.15 to 2.24 with the reduction of coal pillar width. The mining of closely spaced coal seams exhibits a pressure relief effect, and the abutment pressure concentration coefficient under coal pillars is higher than that under the goaf working face. When the underlying working face passes through residual coal pillars, disasters are prone to occur. This is attributed to the superposition of concentrated stress and advanced abutment pressure, combined with vertical splitting and subsidence of the upper rock stratum, which results in sudden stress release. The multitechnology integrated monitoring system and quantitative safety criteria established in this study provide new theoretical foundations and engineering practice references for safe mining under similar geological conditions.