Study on mechanical properties and acoustic emission evolution law of raw coal in water-mechanical coupling environment

This study addresses the critical issue of water-coal interaction in deep coal mining, which affects safe and efficient production. Taking raw coal samples from the Wu Group of Pingmei No. 11 Mine as the research object, uniaxial compression and acoustic emission monitoring tests were conducted under different water immersion times (0 h, 4 h, 8 h, 12 h, 24 h, 48 h). The mechanical properties, deformation and failure behaviors, and energy evolution patterns of water-bearing coal samples were systematically investigated. The results show that the the stress-strain relationship curves of coal samples with different moisture contents exhibit four distinct stages: the crack compaction stage, the linear elastic stage, the plastic deformation stage, and the post-peak failure stage. With increasing moisture content, the failure morphology of the curves transitions from brittle to ductile. The elastic modulus, deformation modulus, and peak strength of the coal samples decrease significantly following a quadratic function with increasing moisture content, while the softening coefficient increases in a quadratic function form. Acoustic emission activity can be divided into three stages: a quiet period, a slow increase period, and a sharp increase period, which correspond to the crack compaction stage, the linear elastic stage, and the yield-failure stage in the stress-strain process, respectively. Analysis based on the energy dissipation theory indicates that only a small portion of the energy absorbed by coal samples during compression is stored as elastic energy, while most of the energy is dissipated in irreversible processes such as pore compaction, crack sliding, and crack propagation. Both the total absorbed energy and the releasable elastic energy before the peak decrease in a quadratic function form with increasing moisture content. This study provides important experimental evidence and a theoretical reference for the stability evaluation and disaster prevention and control of deep water-bearing coal masses.