Axial Compressive Behavior of Carbon Fiber Reinforced Polymer Encased Square Coal Pillar: Experiments and Simulations

ABSTRACT Carbon fiber reinforced polymer (CFRP) encased coal pillar as an innovative support system has attracted growing interest for enhancing stability in underground coal mines. Although CFRP confinement of cylindrical coal samples has been widely studied, the mechanical behavior of square coal pillars commonly found in room‐and‐pillar goafs remains poorly understood and differs significantly. Accordingly, uniaxial compression tests were conducted on CFRP‐encased square coal pillars (CSCP) with 0–4 layers, and a coupled discrete element method–finite difference method (DEM–FDM) numerical model was developed to quantitatively and qualitatively analyze their macroscopic and meso‐mechanical behaviors. The results show that CFRP confinement markedly altered the stress–strain behavior of square coal pillars, inducing double‐peaked curves with post‐peak strengthening behavior that became more pronounced with increasing layers. CFRP wrapping transformed the failure mode from brittle to ductile, with 3‐layer confinement achieving a peak ductility 4.48 times that of unconfined square coal pillars (USCP). Compared to the intense acoustic emission (AE) burst during post‐peak failure in USCP, CSCP exhibited sustained activity before and after the first peak, yet remained stable and gradual during the stress‐maintenance and strengthening stages. This study offers guidance for stable and sustainable mining of residual coal pillars in abandoned mines.