Preparation of a surrogate material for coal creep and the simulation of its damage evolution emulating the coal pillar creep

Surrogate materials were fabricated to investigate the creep damage characteristics of coal pillars in the long wall mining method. Similarity ratios for coal creep viscosity coefficient and creep rate were determined from analyzes derived from the fractional creep constitutive equation. Surrogate materials consisting of sand, paraffin, vaseline, and silicone oil, were prepared to simulate creep behavior. The creep characteristics of these surrogate materials were identified, and the compositions including the ratios of aggregate to binder, and paraffin to vaseline and silicone oil were determined. A physical similarity model was established to calculate the stress and deformation, and determine the damage characteristics of a coal pillar. The results indicate that the stress in the coal pillar decreases over time, and the maximum principal stress shifts toward the center before eventually taking an arc-shaped distribution. The vertical and horizontal distortions of the coal pillar decrease gradually from the coal wall on each side toward the center, resulting in a convex and inverted S-shaped deformation pattern, respectively. The coal pillar develops progressive damage on both sides, with the damaged area gradually increasing toward the middle section, ultimately leading to the collapse of the entire coal pillar. These findings provide valuable insight into the preparation of creep surrogate materials and the management of coal pillar stability.