Investigation on the long-term damage evolution of a strip coal pillar.

The long-term stability of water-immersed coal pillars in proximity to urban areas is critical for ensuring the safety of urban development. This study investigates the creep damage evolution in strip coal pillars through a comprehensive approach integrating in-situ investigations, laboratory experiments, and numerical modeling based on a real-world case study. The analysis focuses on the evolution of stress distribution, creep damage propagation, and the mechanisms driving continuous damage in coal pillars. Findings indicate that in the studied case, concentrated stress around the elastic-plastic boundary progresses toward the central region of the coal pillar as creep damage expands. Initially, the propagation of creep damage is rapid but decelerates due to the residual strength of damaged coal, which bears the overburden pressure and provides lateral constraint. The state of creep damage expansion in a coal pillar depends on the evolution of triaxial creep strength of coal induced by the stress conditions of the intact coal body, which will be changed by the transferred overburden pressure and increased confining pressure.