Creep Damage Evolution Law and Stability Analysis of Remnant Coal Pillars in Longwall Goafs

Abstract

Remnant coal pillars in longwall goaf are vulnerable to creep deformation, damage, and instability under sustained pressure from the overlying strata. To study the creep damage status of coal pillars, we first built a mechanical model of the pillar–roof (P–R) structure. The stress and deformation analytical equations in the viscoelastic and viscoplastic zones of the coal pillar were then constructed following the fractional creep damage constitutive model and the elastic–viscoelastic correspondence theory. The coal pillar creep stress, deformation, and damage development laws were analyzed. The findings indicated that the abutment stress decreases as the creep time increases, and the peak stress gradually shifts to the coal pillar. Finally, a mechanical instability model of the P–R structure based on the coal pillar bearing capacity was established. The instability index and critical elastic kernel ratio for P–R structures considering the creep effect were presented. Moreover, the effects of coal seam depth, coal pillar width, and roof cracking angle on creep damage and coal pillar stability were studied. The findings of this study can be used to optimize the settings for coal pillars and analyze the stability of the remnant coal pillars in goafs.