A study on the effect of water immersion on the viscoelastic-plastic mechanical properties of coal

CHEN Zheng; YANG Tao; REN Fengfei; ZHANG Tianzi; LI Ze; ZHONG Hao; YI Hangyang

doi:10.19956/j.cnki.ncist.2025.03.002

Abstract：Aiming at the problem of mechanical property degradation of coal pillars in underground reservoirs of coal mines caused by long-term erosion of mine water,this study adopts uniaxial compression,triaxial com-pression,and graded creep test methods,sets up multiple groups of coal samples with different immersion dura-tions,and systematically analyzes the influence of immersion on the viscoelastic-plastic mechanical properties of coal.The results show that with the extension of immersion time,the elastic modulus of coal decays expo-nentially,and the decrease reaches 33.7％after 8 weeks;the cohesion and internal friction angle decrease by 12.55％and 29.2％,respectively,and the water-rock interaction reduces the strength of coal through mecha-nisms such as pore expansion,mineral reaction,and particle friction weakening;Poisson's ratio does not show a clear attenuation law due to the anisotropic response of coal microstructure.In the creep test,the instantaneous strain and creep strain of the water-immersed coal increase with the increase of immersion time,and the long-term strength decreases by 28.57％～42.85％compared with the unimmersed sample,indicating that the water chemical effect significantly reduces the mechanical properties of coal.Based on the fractional Burgers model,damage variables and effective stress correction terms were introduced to construct a creep constitutive model that can characterize the entire process of coal rock creep.The accuracy and applicability of the model to the entire creep process were verified by fitting the experimental data.The research results provide theoretical sup-port for the long-term stability evaluation of coal pillar dams in underground reservoirs in coal mines.