Stress Transfer Law of the Floor of Overlying Residual Coal Pillars and Roadway Surrounding Rock Deformation and Support Technology When Crossing Residual Coal Pillars

Abstract

To address severe mining hazards such as intense ground pressure, roof fragmentation, and support instability encountered when longwall faces pass beneath residual coal pillars in close-proximity coal seams, this study investigates the mining conditions of an inclined residual coal pillar in a shallow-buried, close-spaced coal seam at the Daliuta Coal Mine in the Shendong Mining Area. A comprehensive approach integrating theoretical analysis, numerical simulation, fiber-optic monitoring, and field measurements was employed to investigate the stress evolution of surrounding rock and mining-induced pressure response. A floor stress transfer model beneath the upper residual coal pillar was established, revealing stress transmission characteristics into the underlying strata, and numerical simulations confirmed that the stress-enhanced zone exhibits an ellipsoidal distribution and gradually attenuates with depth. Full-process simulations of the working face during the “entry–passage–exit” stages showed that stress concentration on the right side of the pillar consistently exceeded that on the left, whereas horizontal stress in the underlying coal wall increased with advance distance and peaked during the exit stage. The maximum stress concentration reached 12.83 MPa in the pillar and 15.74 MPa in the lower coal seam. Meanwhile, the peak advance abutment pressure increased from 6.47 MPa during the entry stage to 11.44 MPa during the exit stage, following the pattern of “exit > passage > entry.” Fiber-optic borehole monitoring indicated that the stress peak beneath the residual coal pillar reached 2.72 MPa, significantly higher than that beneath the goaf, and exhibited a dynamic “rise–peak–fall” evolution. Field monitoring further confirmed that the exit stage represents the most critical risk zone, with hydraulic support resistance peaking at 18,455 kN per support and a maximum pressure influence range of 7.5 m. Finally, integrating the theory of rock beam structures in shallow-buried coal seams, this study proposes that the rated working resistance of supports during the coal pillar extraction phase should not be less than 15,000 kN per frame. It further recommends implementing proactive control measures such as coal pillar reinforcement support to enhance load transfer. This study systematically elucidates the dynamic stress response mechanism of surrounding rock during the process of mining through residual coal pillars in close-to-the-face coal seams. It identifies the characteristics of intense mining pressure and key prevention and control priorities during the coal pillar extraction phase, providing theoretical foundations and engineering practice references for safe and efficient mining in similar geological conditions.